Climate Change O

Climate Change O
Climate change
and water
O
bservational records and climate projections provide abundant evidence that freshwater resources
are vulnerable and have the potential to be strongly impacted by climate change, with wide-ranging
consequences for human societies and ecosystems.
The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws
together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of
climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality,
use and management. It takes into account current and projected regional key vulnerabilities, prospects for
adaptation, and the relationships between climate change mitigation and water. Its objectives are:
Text in the Technical Paper carefully follows the text of the underlying IPCC Reports, especially the Fourth
Assessment. It reflects the balance and objectivity of those Reports and, where the text differs, this is with the
purpose of supporting and/or explaining further the conclusions of those Reports. Every substantive paragraph
is sourced back to an IPCC Report.
The Intergovernmental Panel on Climate Change (IPCC) was set up jointly by the World Meteorological
Organization and the United Nations Environment Programme to provide an authoritative international assessment
of scientific information on climate change. Climate Change and Water is one of six Technical Papers prepared
by the IPCC to date. It was prepared in response to a request from the World Climate Programme – Water and
the International Steering Committee of the Dialogue on Water and Climate.
climate change and water
• To improve understanding of the links between both natural and anthropogenically induced climate change,
its impacts, and adaptation and mitigation response options, on the one hand, and water-related issues, on
the other;
• To communicate this improved understanding to policymakers and stakeholders.
IPCC Technical Paper VI
Intergovernmental Panel on Climate Change
INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE
UNEP
WMO
Climate Change and Water
Edited by
Bryson Bates
CSIRO
Australia
Zbigniew W. Kundzewicz
Polish Academy of Sciences, Poland
and Potsdam Institute for Climate
Impact Research, Germany
Shaohong Wu
Chinese Academy of Sciences
China
Jean Palutikof
Met Office Hadley Centre
United Kingdom
This is a Technical Paper of the Intergovernmental Panel on Climate Change prepared in response to a decision
of the Panel. The material herein has undergone expert and government review, but has not been considered by
the Panel for possible acceptance or approval.
June 2008
This paper was prepared under the management of the IPCC Working Group II
Technical Support Unit
Please cite this Technical Paper as:
Bates, B.C., Z.W. Kundzewicz, S. Wu and J.P. Palutikof, Eds., 2008: Climate Change and Water. Technical
Paper of the Intergovernmental Panel on Climate Change, IPCC Secretariat, Geneva, 210 pp.
© 2008, Intergovernmental Panel on Climate Change
ISBN: 978-92-9169-123-4
Cover photo: © Simon Fraser/Science Photo Library
Contents
Preface
Acknowledgments
Executive Summary
1. Introduction to climate change and water
1.1 Background
1.2 Scope
1.3 The context of the Technical Paper: socio-economic and environmental conditions
1.3.1 Observed changes
1.3.2 Projected changes
vii
viii
1
5
7
7
8
8
9
1.4 Outline
2. Observed and projected changes in climate as they relate to water
2.1 Observed changes in climate as they relate to water
11
13
15
2.2 Influences and feedbacks of hydrological changes on climate
23
2.3 Projected changes in climate as they relate to water
24
2.1.1
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
2.1.7
Precipitation (including extremes) and water vapour
Snow and land ice
Sea level
Evapotranspiration
Soil moisture
Runoff and river discharge
Patterns of large-scale variability
2.2.1 Land surface effects
2.2.2 Feedbacks through changes in ocean circulation
2.2.3 Emissions and sinks affected by hydrological processes or biogeochemical feedbacks
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
2.3.6
2.3.7
Precipitation (including extremes) and water vapour
Snow and land ice
Sea level
Evapotranspiration
Soil moisture
Runoff and river discharge
Patterns of large-scale variability
3. Linking climate change and water resources: impacts and responses
3.1 Observed climate change impacts
3.1.1 Observed effects due to changes in the cryosphere
3.1.2 Hydrology and water resources
3.2 Future changes in water availability and demand due to climate change
3.2.1 Climate-related drivers of freshwater systems in the future
3.2.2 Non-climatic drivers of freshwater systems in the future
15
19
20
20
21
21
22
23
24
24
25
27
28
29
29
29
31
33
35
35
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38
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43
iii
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8
Impacts of climate change on freshwater availability in the future
Impacts of climate change on freshwater demand in the future
Impacts of climate change on water stress in the future
Impacts of climate change on costs and other socio-economic aspects of freshwater
Freshwater areas and sectors highly vulnerable to climate change
Uncertainties in the projected impacts of climate change on freshwater systems
3.3 Water-related adaptation to climate change: an overview
4. Climate change and water resources in systems and sectors
4.1 Ecosystems and biodiversity
4.1.1 Context
4.1.2 Projected changes in hydrology and implications for global biodiversity
4.1.3 Impacts of changes in hydrology on major ecosystem types
48
53
55
55
55
55
4.2 Agriculture and food security, land use and forestry
59
4.3 Human health
67
4.4 Water supply and sanitation
69
4.5 Settlements and infrastructure
73
4.6 Economy: insurance, tourism, industry, transportation
74
4.2.1
4.2.2
4.2.3
4.2.4
Context
Observations
Projections
Adaptation, vulnerability and sustainable development
4.3.1
4.3.2
4.3.3
4.3.4
Context
Observations
Projections
Adaptation, vulnerability and sustainable development
4.4.1
4.4.2
4.4.3
4.4.4
Context
Observations
Projections
Adaptation, vulnerability and sustainable development
4.5.1 Settlements
4.5.2 Infrastructure
4.5.3 Adaptation
4.6.1 Context
4.6.2 Socio-economic costs, mitigation, adaptation, vulnerability, sustainable development
5. Analysing regional aspects of climate change and water resources
5.1 Africa
5.1.1
5.1.2
5.1.3
5.1.4
Context
Current observations
Projected changes
Adaptation and vulnerability
5.2.1
5.2.2
5.2.3
5.2.4
Context
Observed impacts of climate change on water
Projected impact of climate change on water and key vulnerabilities
Adaptation and vulnerability
59
60
60
63
67
69
69
69
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69
70
71
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74
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75
77
79
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79
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85
5.2 Asia
85
5.3 Australia and New Zealand
90
5.3.1 Context
iv
44
44
45
45
47
47
85
85
87
88
90
5.3.2 Observed changes
5.3.3 Projected changes
5.3.4 Adaptation and vulnerability
90
91
92
5.4 Europe
93
5.5 Latin America
96
5.4.1
5.4.2
5.4.3
5.4.4
Context
Observed changes
Projected changes
Adaptation and vulnerability
5.5.1
5.5.2
5.5.3
5.5.4
Context
Observed changes
Projected changes
Adaptation and vulnerability
93
93
93
95
96
96
98
100
5.6 North America
102
5.7 Polar regions
106
5.8 Small islands
109
5.6.1 Context and observed changes
5.6.2 Projected change and consequences
5.6.3 Adaptation
5.7.1
5.7.2
5.7.3
5.7.4
Context
Observed changes
Projected changes
Adaptation and vulnerability
5.8.1 Context
5.8.2 Observed climatic trends and projections in island regions
5.8.3 Adaptation, vulnerability and sustainability
6. Climate change mitigation measures and water
6.1 Introduction
6.2 Sector-specific mitigation
6.2.1 Carbon dioxide capture and storage (CCS)
6.2.2 Bio-energy crops
6.2.3 Biomass electricity
6.2.4 Hydropower
6.2.5 Geothermal energy
6.2.6 Energy use in buildings
6.2.7 Land-use change and management
6.2.8 Cropland management (water)
6.2.9 Cropland management (reduced tillage)
6.2.10 Afforestation or reforestation
6.2.11 Avoided/reduced deforestation
6.2.12 Solid waste management; wastewater treatment
6.2.13 Unconventional oil
6.3 Effects of water management policies and measures on GHG emissions and mitigation
6.3.1
6.3.2
6.3.3
6.3.4
Hydro dams
Irrigation
Residue return
Drainage of cropland
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108
109
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109
111
115
117
117
117
117
119
119
119
119
119
120
120
120
121
121
122
122
122
122
122
123
6.3.5 Wastewater treatment
6.3.6 Desalinisation
6.3.7 Geothermal energy
123
124
124
6.4 Potential water resource conflicts between adaptation and mitigation
7. Implications for policy and sustainable development
7.1 Implication for policy by sector
7.2 The main water-related projected impacts by regions
7.3 Implications for climate mitigation policy
7.4 Implications for sustainable development
8. Gaps in knowledge and suggestions for further work
8.1 Observational needs
8.2 Understanding climate projections and their impacts
124
125
127
128
130
130
133
135
135
8.3 Adaptation and mitigation
References
Appendix I: Climate model descriptions
Appendix II: Glossary
Appendix III: Acronyms, chemical symbols, scientific units
Appendix IV: List of Authors
Appendix V: List of Reviewers
Appendix VI: Permissions to publish
Index
136
139
165
167
183
185
187
191
193
8.2.1 Understanding and projecting climate change
8.2.2 Water-related impacts
vi
135
136
Preface
The Intergovernmental Panel on Climate Change (IPCC)
Technical Paper on Climate Change and Water is the sixth
paper in the IPCC Technical Paper series and was produced in
response to a proposal by the Secretariat of the World Climate
Programme – Water (WCP-Water) and the International
Steering Committee of the Dialogue on Water and Climate
at the 19th Plenary Session of the IPCC which took place in
Geneva in April 2002. A consultative meeting on Climate
Change and Water was held in Geneva in November 2002 and
recommended the preparation of a Technical Paper on Climate
Change and Water instead of preparing a Special Report to
address this subject. Such a document was to be based primarily
on the findings of the Fourth Assessment Report of the IPCC,
but also earlier IPCC publications. The Panel also decided that
water should be treated as cross cutting theme in the Fourth
Assessment Report.
The Technical Paper addresses the issue of freshwater. Sealevel rise is dealt with only insofar as it can lead to impacts
on freshwater in coastal areas and beyond. Climate, freshwater,
biophysical and socio-economic systems are interconnected in
complex ways. Hence, a change in any one of these can induce
a change in any other. Freshwater-related issues are critical in
determining key regional and sectoral vulnerabilities. Therefore,
the relationship between climate change and freshwater
resources is of primary concern to human society and also has
implications for all living species.
An interdisciplinary writing team of Lead Authors was selected
by the three IPCC Working Group Bureaus with the aim of
achieving a regional and topical balance. Like all IPCC Technical
Papers, this product too is based on the material of previously
approved/accepted/adopted IPCC reports and underwent a
simultaneous expert and Government review, followed by a
final Government review. The Bureau of the IPCC acted in the
capacity of an editorial board to ensure that the review comments
were adequately addressed by the Lead Authors in the finalisation
of the Technical Paper.
The Bureau met in its 37th Session in Budapest in April 2008
and considered the major comments received during the final
Government review. In the light of its observations and requests,
the Lead Authors finalised the Technical Paper, after which the
Bureau authorised its release to the public.
We owe a large debt of gratitude to the Lead Authors (listed
in the Paper) who gave of their time very generously and who
completed the Technical Paper according to schedule. We would
like to thank Dr. Jean Palutikof, Head of the Technical Support
Unit of IPCC Working Group II, for her skilful leadership through
the production of this Paper.
Rajendra K. Pachauri
Chairman of the IPCC
Renate Christ
Secretary of the IPCC
Osvaldo Canziani
Co-Chair IPCC Working Group II
Martin Parry
Co-Chair IPCC Working Group II
vii
Acknowledgments
We thank the Working Group II Technical Support Unit, especially Norah Pritchard and Clair Hanson, for their hard
work in the preparation of this Technical Paper.
The Government of Canada kindly agreed to host the second Lead Author meeting, and we thank Terry Prowse for
undertaking the hard work of organisation in Victoria, British Columbia.
Maurice Roos, from the State of California Department of Water Resources, and Bill Girling, from Manitoba Hydro,
attended the second Lead Author meeting to provide advice and suggestions from a user perspective.
Marilyn Anderson prepared the Index and Nancy Boston copy edited the text.
Thanks go to all the authors, their families, institutions and governments, for making this paper possible.
Bryson Bates
Zbyszek Kundzewicz
Shaohong Wu
Jean Palutikof
viii
23 June 2008
Climate Change and Water
This Technical Paper was requested by IPCC Plenary in response to suggestions by the World Climate
Programme - Water, the Dialogue on Water and other organisations concerned with the provision of water.
It was prepared under the auspices of the IPCC Chair, Dr. R.K. Pachauri.
Coordinating Lead Authors
Bryson Bates (Australia), Zbigniew W. Kundzewicz (Poland) and Shaohong Wu (China)
Lead Authors
Nigel Arnell (UK), Virginia Burkett (USA), Petra Döll (Germany), Daniel Gwary (Nigeria), Clair Hanson
(UK), BertJan Heij (The Netherlands), Blanca Elena Jiménez (Mexico), Georg Kaser (Austria), Akio Kitoh
(Japan), Sari Kovats (UK), Pushpam Kumar (UK), Christopher H.D. Magadza (Zimbabwe), Daniel Martino
(Uruguay), Luis José Mata (Germany/Venezuela), Mahmoud Medany (Egypt), Kathleen Miller (USA), Taikan
Oki (Japan), Balgis Osman (Sudan), Jean Palutikof (UK), Terry Prowse (Canada), Roger Pulwarty (USA/
Trinidad and Tobago), Jouni Räisänen (Finland), James Renwick (New Zealand), Francesco Nicola Tubiello
(USA/IIASA/Italy), Richard Wood (UK) and Zong-Ci Zhao (China)
Contributing Authors
Julie Arblaster (Australia), Richard Betts (UK), Aiguo Dai (USA), Christopher Milly (USA), Linda Mortsch
(Canada), Leonard Nurse (Barbados), Richard Payne (Australia), Iwona Pinskwar (Poland) and Tom Wilbanks
(USA)
Executive Summary
Executive Summary
Observational records and climate projections provide abundant evidence that freshwater resources
are vulnerable and have the potential to be strongly impacted by climate change, with wide-ranging
consequences for human societies and ecosystems.
Observed warming over several decades has been linked
to changes in the large-scale hydrological cycle such as:
increasing atmospheric water vapour content; changing
precipitation patterns, intensity and extremes; reduced snow
cover and widespread melting of ice; and changes in soil
moisture and runoff. Precipitation changes show substantial
spatial and inter-decadal variability. Over the 20th century,
precipitation has mostly increased over land in high northern
latitudes, while decreases have dominated from 10°S to 30°N
since the 1970s. The frequency of heavy precipitation events (or
proportion of total rainfall from heavy falls) has increased over
most areas (likely1). Globally, the area of land classified as very
dry has more than doubled since the 1970s (likely). There have
been significant decreases in water storage in mountain glaciers
and Northern Hemisphere snow cover. Shifts in the amplitude
and timing of runoff in glacier- and snowmelt-fed rivers, and in
ice-related phenomena in rivers and lakes, have been observed
(high confidence). [2.12]
Climate model simulations for the 21st century are consistent
in projecting precipitation increases in high latitudes (very
likely) and parts of the tropics, and decreases in some subtropical and lower mid-latitude regions (likely). Outside
these areas, the sign and magnitude of projected changes
varies between models, leading to substantial uncertainty
in precipitation projections.3 Thus projections of future
precipitation changes are more robust for some regions than for
others. Projections become less consistent between models as
spatial scales decrease. [2.3.1]
consequences for the risk of rain-generated floods. At the same
time, the proportion of land surface in extreme drought at any
one time is projected to increase (likely), in addition to a tendency
for drying in continental interiors during summer, especially in
the sub-tropics, low and mid-latitudes. [2.3.1, 3.2.1]
Water supplies stored in glaciers and snow cover are
projected to decline in the course of the century, thus
reducing water availability during warm and dry periods
(through a seasonal shift in streamflow, an increase in the
ratio of winter to annual flows, and reductions in low flows) in
regions supplied by melt water from major mountain ranges,
where more than one-sixth of the world’s population currently
live (high confidence). [2.1.2, 2.3.2, 2.3.6]
Higher water temperatures and changes in extremes,
including floods and droughts, are projected to affect water
quality and exacerbate many forms of water pollution –
from sediments, nutrients, dissolved organic carbon, pathogens,
pesticides and salt, as well as thermal pollution, with possible
negative impacts on ecosystems, human health, and water system
reliability and operating costs (high confidence). In addition,
sea-level rise is projected to extend areas of salinisation of
groundwater and estuaries, resulting in a decrease of freshwater
availability for humans and ecosystems in coastal areas.
[3.2.1.4, 4.4.3]
By the middle of the 21st century, annual average river runoff
and water availability are projected to increase as a result of
climate change4 at high latitudes and in some wet tropical
areas, and decrease over some dry regions at mid-latitudes
and in the dry tropics.5 Many semi-arid and arid areas (e.g., the
Mediterranean Basin, western USA, southern Africa and northeastern Brazil) are particularly exposed to the impacts of climate
change and are projected to suffer a decrease of water resources
due to climate change (high confidence). [2.3.6]
Globally, the negative impacts of future climate change on
freshwater systems are expected to outweigh the benefits
(high confidence). By the 2050s, the area of land subject to
increasing water stress due to climate change is projected to
be more than double that with decreasing water stress. Areas
in which runoff is projected to decline face a clear reduction in
the value of the services provided by water resources. Increased
annual runoff in some areas is projected to lead to increased
total water supply. However, in many regions, this benefit is
likely to be counterbalanced by the negative effects of increased
precipitation variability and seasonal runoff shifts in water
supply, water quality and flood risks (high confidence). [3.2.5]
Increased precipitation intensity and variability are
projected to increase the risks of flooding and drought
in many areas. The frequency of heavy precipitation events
(or proportion of total rainfall from heavy falls) will be very
likely to increase over most areas during the 21st century, with
Changes in water quantity and quality due to climate change
are expected to affect food availability, stability, access and
utilisation. This is expected to lead to decreased food security and
increased vulnerability of poor rural farmers, especially in the arid
and semi-arid tropics and Asian and African megadeltas. [4.2]
See Box 1.1.
Numbers inside square brackets relate to sections in the main body of the Technical Paper.
3
Projections considered are based on the range of non-mitigation scenarios developed by the IPCC Special Report on Emissions Scenarios
(SRES).
4
This statement excludes changes in non-climatic factors, such as irrigation.
5
These projections are based on an ensemble of climate models using the mid-range SRES A1B non-mitigation emissions scenario. Consideration
of the range of climate responses across SRES scenarios in the mid-21st century suggests that this conclusion is applicable across a wider range
of scenarios.
1
2
Executive Summary
Climate change affects the function and operation of
existing water infrastructure – including hydropower,
structural flood defences, drainage and irrigation systems
– as well as water management practices. Adverse effects
of climate change on freshwater systems aggravate the
impacts of other stresses, such as population growth, changing
economic activity, land-use change and urbanisation (very high
confidence). Globally, water demand will grow in the coming
decades, primarily due to population growth and increasing
affluence; regionally, large changes in irrigation water demand
as a result of climate change are expected (high confidence).
[1.3, 4.4, 4.5, 4.6]
Current water management practices may not be robust
enough to cope with the impacts of climate change on water
supply reliability, flood risk, health, agriculture, energy and
aquatic ecosystems. In many locations, water management
cannot satisfactorily cope even with current climate variability,
so that large flood and drought damages occur. As a first step,
improved incorporation of information about current climate
variability into water-related management would assist
adaptation to longer-term climate change impacts. Climatic and
non-climatic factors, such as growth of population and damage
potential, would exacerbate problems in the future (very high
confidence). [3.3]
Climate change challenges the traditional assumption
that past hydrological experience provides a good guide to
future conditions. The consequences of climate change may
alter the reliability of current water management systems and
water-related infrastructure. While quantitative projections of
changes in precipitation, river flows and water levels at the
river-basin scale are uncertain, it is very likely that hydrological
characteristics will change in the future. Adaptation procedures
and risk management practices that incorporate projected
hydrological changes with related uncertainties are being
developed in some countries and regions. [3.3]
Adaptation options designed to ensure water supply
during average and drought conditions require integrated
demand-side as well as supply-side strategies. The former
improve water-use efficiency, e.g., by recycling water. An
expanded use of economic incentives, including metering and
pricing, to encourage water conservation and development of
water markets and implementation of virtual water trade, holds
considerable promise for water savings and the reallocation of
water to highly valued uses. Supply-side strategies generally
involve increases in storage capacity, abstraction from water
courses, and water transfers. Integrated water resources
management provides an important framework to achieve
adaptation measures across socio-economic, environmental and
administrative systems. To be effective, integrated approaches
must occur at the appropriate scales. [3.3]
Mitigation measures can reduce the magnitude of impacts
of global warming on water resources, in turn reducing
adaptation needs. However, they can have considerable
negative side effects, such as increased water requirements
for afforestation/reforestation activities or bio-energy crops,
if projects are not sustainably located, designed and managed.
On the other hand, water management policy measures,
e.g., hydrodams, can influence greenhouse gas emissions.
Hydrodams are a source of renewable energy. Nevertheless, they
produce greenhouse gas emissions themselves. The magnitude
of these emissions depends on specific circumstance and mode
of operation. [Section 6]
Water resources management clearly impacts on many
other policy areas, e.g., energy, health, food security and nature
conservation. Thus, the appraisal of adaptation and mitigation
options needs to be conducted across multiple water-dependent
sectors. Low-income countries and regions are likely to remain
vulnerable over the medium term, with fewer options than highincome countries for adapting to climate change. Therefore,
adaptation strategies should be designed in the context of
development, environment and health policies. [Section 7]
Several gaps in knowledge exist in terms of observations
and research needs related to climate change and water.
Observational data and data access are prerequisites for adaptive
management, yet many observational networks are shrinking.
There is a need to improve understanding and modelling of
climate changes related to the hydrological cycle at scales
relevant to decision making. Information about the waterrelated impacts of climate change is inadequate – especially with
respect to water quality, aquatic ecosystems and groundwater
– including their socio-economic dimensions. Finally, current
tools to facilitate integrated appraisals of adaptation and
mitigation options across multiple water-dependent sectors are
inadequate. [Section 8]
1
Introduction to climate change
and water
Section 1
1.1 Background
The idea of a special IPCC publication dedicated to water
and climate change dates back to the 19th IPCC Session held
in Geneva in April 2002, when the Secretariat of the World
Climate Programme – Water and the International Steering
Committee of the Dialogue on Water and Climate requested
that the IPCC prepare a Special Report on Water and Climate.
A consultative meeting on Climate Change and Water held in
Geneva in November 2002 concluded that the development of
such a report in 2005 or 2006 would have little value, as it would
quickly be superseded by the Fourth Assessment Report (AR4),
which was planned for completion in 2007. Instead, the meeting
recommended the preparation of a Technical Paper on Climate
Change and Water that would be based primarily on AR4 but
would also include material from earlier IPCC publications.
An interdisciplinary writing team was selected by the three
IPCC Working Group Bureaux with the aim of achieving
regional and topical balance, and with multiple relevant
disciplines being represented. United Nations (UN) agencies,
non-governmental organisations (NGOs) and representatives
from relevant stakeholder communities, including the private
sector, have been involved in the preparation of this Technical
Paper and the associated review process.
IPCC guidelines require that Technical Papers are derived
from:
(a) the text of IPCC Assessment Reports and Special Reports
and the portions of material in cited studies that were relied
upon in these reports;
(b) relevant models with their assumptions, and scenarios
based on socio-economic assumptions, as they were used
to provide information in those IPCC Reports.
These guidelines are adhered to in this Technical Paper.
1.2 Scope
Introduction to climate change and water
these induces a change in another. Anthropogenic climate change
adds a major pressure to nations that are already confronting the
issue of sustainable freshwater use. The challenges related to
freshwater are: having too much water, having too little water,
and having too much pollution. Each of these problems may be
exacerbated by climate change. Freshwater-related issues play a
pivotal role among the key regional and sectoral vulnerabilities.
Therefore, the relationship between climate change and
freshwater resources is of primary concern and interest.
So far, water resource issues have not been adequately addressed
in climate change analyses and climate policy formulations.
Likewise, in most cases, climate change problems have not been
adequately dealt with in water resources analyses, management
and policy formulation. According to many experts, water and
its availability and quality will be the main pressures on, and
issues for, societies and the environment under climate change;
hence it is necessary to improve our understanding of the
problems involved.
The objectives of this Technical Paper, as set out in IPCC-XXI
– Doc. 96, are summarised below:
•
to improve our understanding of the links between both
natural and anthropogenically induced climate change, its
impacts, and adaptation and mitigation response options,
on the one hand, and water-related issues, on the other;
•
to inform policymakers and stakeholders about the
implications of climate change and climate change response
options for water resources, as well as the implications for
water resources of various climate change scenarios and
climate change response options, including associated
synergies and trade-offs.
The scope of this Technical Paper, as outlined in IPCCXXI – Doc. 9, is to evaluate the impacts of climate change
on hydrological processes and regimes, and on freshwater
resources – their availability, quality, uses and management.
The Technical Paper takes into account current and projected
regional key vulnerabilities and prospects for adaptation.
This Technical Paper deals only with freshwater. Sea-level rise
is dealt with only insofar as it can lead to impacts on freshwater
in the coastal zone; for example, salinisation of groundwater.
Reflecting the focus of the literature, it deals mainly with climate
change through the 21st century whilst recognising that, even if
greenhouse gas concentrations were to be stabilised, warming
and sea-level rise would continue for centuries. [WGI SPM]
The Technical Paper is addressed primarily to policymakers
engaged in all areas relevant to freshwater resource management,
climate change, strategic studies, spatial planning and socioeconomic development. However, it is also addressed to the
scientific community working in the area of water and climate
change, and to a broader audience, including NGOs and the
media.
The importance of freshwater to our life support system is
widely recognised, as can be seen clearly in the international
context (e.g., Agenda 21, World Water Fora, the Millennium
Ecosystem Assessment and the World Water Development
Report). Freshwater is indispensable for all forms of life and
is needed, in large quantities, in almost all human activities.
Climate, freshwater, biophysical and socio-economic systems
are interconnected in complex ways, so a change in any one of
Since material on water and climate change is scattered
throughout the IPCC’s Fourth Assessment and Synthesis Reports,
it is useful to have a compact and integrated publication focused
on water and climate change. The present Technical Paper also
refers to earlier IPCC Assessment and Special Reports, where
necessary. The added value of this Technical Paper lies in the
distillation, prioritisation, synthesis and interpretation of those
materials.
6
‘Scoping Paper for a possible Technical Paper on Climate Change and Water’. Available at: http://www.ipcc.ch/meetings/session21.htm.
Introduction to climate change and water
Text in the Technical Paper carefully follows the text of the
underlying IPCC Reports. It reflects the balance and objectivity
of those Reports and, where the text differs, this is with the
purpose of supporting and/or explaining further the Reports’
conclusions. Every substantive paragraph is sourced back to an
IPCC Report. The source is provided within square brackets,
generally at the end of the paragraph (except where parts of
a paragraph are sourced from more than one IPCC document,
in which case the relevant IPCC source is located after the
appropriate entry). The following conventions have been used.
•
The Fourth Assessment Report (AR4) is the most frequently
cited IPCC publication and is represented by, for example,
[WGII 3.5], which refers to AR4 Working Group II Chapter
3 Section 3.5. See IPCC (2007a, b, c, d).
•
Where material is taken from other IPCC sources, the
following acronyms are used: TAR (Third Assessment
Report: IPCC 2001a, b, c), RICC (Special Report on
Regional Impacts of Climate Change: Watson et al., 1997),
LULUCF (Special Report on Land Use, Land-Use Change
and Forestry: IPCC, 2000), SRES (Special Report on
Emissions Scenarios: Nakićenović and Swart, 2000), CCB
(Technical Paper V – Climate Change and Biodiversity:
Gitay et al., 2002) and CCS (Special Report on Carbon
Dioxide Capture and Storage: Metz et al., 2005). Thus,
[WGII TAR 5.8.3] refers to Section 5.8.3 of Chapter 5 in
the Working Group II Third Assessment Report.
•
Additional sourcing acronyms include ES (Executive
Summary), SPM (Summary for Policymakers), TS
(Technical Summary) and SYR (Synthesis Report), which
all refer to the AR4 unless otherwise indicated.
References to original sources (journals, books and reports) are
placed after the relevant sentence, within round brackets.
1.3 The context of the Technical Paper:
socio-economic and environmental
conditions
This Technical Paper explores the relationships between climate
change and freshwater, as set out in IPCC Assessment and
Special Reports. These relationships do not exist in isolation,
but in the context of, and interacting with, socio-economic and
environmental conditions. In this section, we describe the major
features of these conditions as they relate to freshwater, both
observed and projected.
Many non-climatic drivers affect freshwater resources at all
scales, including the global scale (UN, 2003). Water resources,
both in terms of quantity and quality, are critically influenced
by human activity, including agriculture and land-use change,
construction and management of reservoirs, pollutant emissions,
and water and wastewater treatment. Water use is linked primarily
to changes in population, food consumption (including type of
7
8
Section 1
diet), economic policy (including water pricing), technology,
lifestyle7 and society’s views about the value of freshwater
ecosystems. In order to assess the relationship between climate
change and freshwater, it is necessary to consider how freshwater
has been, and will be, affected by changes in these non-climatic
drivers. [WGII 3.3.2]
1.3.1
Observed changes
In global-scale assessments, basins are defined as being waterstressed8 if they have either a per capita water availability
below 1,000 m3 per year (based on long-term average runoff)
or a ratio of withdrawals to long-term average annual runoff
above 0.4. A water volume of 1,000 m3 per capita per year is
typically more than is required for domestic, industrial and
agricultural water uses. Such water-stressed basins are located
in northern Africa, the Mediterranean region, the Middle East,
the Near East, southern Asia, northern China, Australia, the
USA, Mexico, north-eastern Brazil and the west coast of South
America (Figure 1.1). The estimates for the population living
in such water-stressed basins range between 1.4 billion and
2.1 billion (Vörösmarty et al., 2000; Alcamo et al., 2003a, b;
Oki et al., 2003; Arnell, 2004). [WGII 3.2]
Water use, in particular that for irrigation, generally increases
with temperature and decreases with precipitation; however,
there is no evidence for a climate-related long-term trend of
water use in the past. This is due, in part, to the fact that water
use is mainly driven by non-climatic factors, and is also due to
the poor quality of water-use data in general, and of time-series
data in particular. [WGII 3.2]
Water availability from surface water sources or shallow
groundwater wells depends on the seasonality and interannual
variability of streamflow, and a secured water supply is determined
by seasonal low flows. In snow-dominated basins, higher
temperatures lead to reduced streamflow and thus decreased
water supply in summer (Barnett et al., 2005). [WGII 3.2]
In water-stressed areas, people and ecosystems are particularly
vulnerable to decreasing and more variable precipitation due to
climate change. Examples are given in Section 5.
In most countries, except for a few industrialised nations, water
use has increased over recent decades, due to population and
economic growth, changes in lifestyle, and expanded water
supply systems, with irrigation water use being by far the most
important cause. Irrigation accounts for about 70% of total water
withdrawals worldwide and for more than 90% of consumptive
water use (i.e., the water volume that is not available for reuse
downstream). [WGII 3.2] Irrigation generates about 40%
of total agricultural output (Fischer et al., 2006). The area of
global irrigated land has increased approximately linearly since
In this context use of water-hungry appliances such as dishwashers, washing machines, lawn sprinklers etc.
Water stress is a concept describing how people are exposed to the risk of water shortage.
Introduction to climate change and water
Section 1
Figure 1.1: Examples of current vulnerabilities of freshwater resources and their management; in the background, a water
stress map based on WaterGAP (Alcamo et al., 2003a). See text for relation to climate change. [WGII Figure 3.2]
1960, at a rate of roughly 2% per annum, from 140 million ha in
1961/63 to 270 million ha in 1997/99, representing about 18%
of today’s total cultivated land (Bruinsma, 2003).
Although the rates of regional population change differ widely
from the global average, the rate of global population increase is
already declining. Global water use is probably increasing due
to economic growth in developing countries, but there are no
reliable data with respect to the rate of increase. [WGII 3.2, 5.3]
The quality of surface water and groundwater has generally
declined in recent decades due principally to growth in
agricultural and industrial activities (UN, 2006). To counter
this problem, many countries (e.g., in the European Union and
Canada) have established or enforced effluent water standards
and have rehabilitated wastewater treatment facilities (GEO-3,
2003). [WGII 3.3.2, Table 8.1]
1.3.2
Projected changes
1.3.2.1
General background
The four IPCC SRES (Special Report on Emissions Scenarios:
Nakićenović and Swart, 2000) storylines, which form the
basis for many studies of projected climate change and water
resources, consider a range of plausible changes in population
and economic activity over the 21st century (see Figure 1.2).
Among the scenarios that assume a world economy dominated
by global trade and alliances (A1 and B1), global population
is expected to increase from today’s 6.6 billion and peak at
8.7 billion in 2050, while in the scenarios with less globalisation
and co-operation (A2 and B2), global population is expected to
increase until 2100, reaching 10.4 billion (B2) and 15 billion
(A2) by the end of the century. In general, all SRES scenarios
depict a society that is more affluent than today, with world gross
domestic product (GDP) rising to 10–26 times today’s levels
by 2100. A narrowing of income differences between world
regions is assumed in all SRES scenarios – with technology
representing a driving force as important as demographic
change and economic development. [SRES SPM]
1.3.2.2
Water resources
Of particular interest for projections of water resources,
with or without climate change, are possible changes in dam
construction and decommissioning, water supply infrastructure,
wastewater treatment and reuse, desalination, pollutant
emissions and land use, particularly with regard to irrigation.
Irrespective of climate change, new dams are expected to be
built in developing countries for hydropower generation as
well as water supply, even though their number is likely to be
small compared to the existing 45,000 large dams. However,
the impacts of a possible future increase in hydropower demand
have not been taken into account (World Commission on Dams,
Introduction to climate change and water
Section 1
is likely to increase. Several of these pollutants are not removed
by current wastewater treatment technology. Modifications of
water quality may be caused by the impact of sea-level rise on
storm-water drainage operations and sewage disposal in coastal
areas. [WGII 3.2.2, 3.4.4]
Economic emphasis
Global integration
Regional emphasis
Environmental emphasis
Figure 1.2: Summary characteristics of the four SRES
storylines (based on Nakićenović and Swart, 2000).
[WGII Figure 2.5]
2000; Scudder, 2005). In developed countries, the number of
dams is very likely to remain stable, and some dams will be
decommissioned. With increased temporal runoff variability
due to climate change, increased water storage behind dams
may be beneficial, especially where annual runoff does not
decrease significantly. Consideration of environmental flow
requirements may lead to further modification of reservoir
operations so that the human use of water resources might be
restricted. Efforts to reach the Millennium Development Goals
(MDGs, see Table 7.1) should lead to improved water sources
and sanitation. In the future, wastewater reuse and desalination
will possibly become important sources of water supply in semiarid and arid regions. However, there are unresolved concerns
regarding their environmental impacts, including those related
to the high energy use of desalination. Other options, such
as effective water pricing policies and cost-effective water
demand management strategies, need to be considered first.
[WGII 3.3.2, 3.4.1, 3.7]
An increase in wastewater treatment in both developed and
developing countries is expected in the future, but point-source
discharges of nutrients, heavy metals and organic substances
are likely to increase in developing countries. In both developed
and developing countries, emissions of organic micro-pollutants
(e.g., endocrine substances) to surface waters and groundwater
may increase, given that the production and consumption of
chemicals, with the exception of a few highly toxic substances,
10
Diffuse emissions of nutrients and pesticides from agriculture
are likely to continue to be important in developed countries
and are very likely to increase in developing countries, thus
critically affecting water quality. According to the four scenarios
of the Millennium Ecosystem Assessment (2005a) (‘Global
orchestration’, ‘Order from strength’, ‘Adapting mosaic’ and
‘TechnoGarden’), global nitrogen fertiliser use will reach 110–
140 Mt by 2050, compared with 90 Mt in 2000. Under three of
the scenarios, there is an increase in nitrogen transport in rivers
by 2050, while under the ‘TechnoGarden’ scenario (similar to
the IPCC SRES scenario B1) there is a reduction (Millennium
Ecosystem Assessment, 2005b). [WGII 3.3.2]
Among the most important drivers of water use are population
and economic development, but also changing societal views
on the value of water. The latter refers to the prioritisation of
domestic and industrial water supply over irrigation water
supply and the efficient use of water, including the extended
application of water-saving technologies and water pricing.
In all four Millennium Ecosystem Assessment scenarios, per
capita domestic water use in 2050 is broadly similar in all world
regions, at around 100 m3/yr, i.e., the European average in 2000
(Millennium Ecosystem Assessment, 2005b). [WGII 3.3.2]
The dominant non-climate-change-related drivers of future
irrigation water use are: the extent of irrigated area, crop
type, cropping intensity and irrigation water-use efficiency.
According to FAO (UN Food and Agriculture Organization)
projections, developing countries, with 75% of the global
irrigated area, are likely to expand their irrigated areas by 0.6%
per year until 2030, while the cropping intensity of irrigated
land is projected to increase from 1.27 to 1.41 crops per year and
irrigation water-use efficiency will increase slightly (Bruinsma,
2003). These estimates exclude climate change, which is
not expected by Bruinsma to affect agriculture before 2030.
Most of the expansion is projected to occur in already waterstressed areas such as southern Asia, northern China, the Near
East and northern Africa. However, a much smaller expansion
of irrigated area is assumed under all four scenarios of the
Millennium Ecosystem Assessment, with global growth rates of
only 0–0.18% per year until 2050. After 2050, the irrigated area
is assumed to stabilise or slightly decline under all scenarios
except ‘Global orchestration’ (similar to the IPCC SRES A1
scenario) (Millennium Ecosystem Assessment, 2005a). In
another study, using a revised A2 population scenario and FAO
long-term projections, increases in global irrigated land of over
40% by 2080 are projected to occur mainly in southern Asia,
Africa and Latin America, corresponding to an average increase
of 0.4% per year (Fischer et al., 2006). [WGII 3.3.2]
Section 1
1.4 Outline
This Technical Paper consists of eight sections. Following the
introduction to the Paper (Section 1), Section 2 is based primarily
on the assessments of Working Group I, and looks at the science
of climate change, both observed and projected, as it relates to
hydrological variables. Section 3 presents a general overview of
observed and projected water-related impacts of climate change,
Introduction to climate change and water
and possible adaptation strategies, drawn principally from the
Working Group II assessments. Section 4 then looks at systems
and sectors in detail, and Section 5 takes a regional approach.
Section 6, based on Working Group III assessments, covers waterrelated aspects of mitigation. Section 7 looks at the implications
for policy and sustainable development, followed by the final
section (Section 8) on gaps in knowledge and suggestions for
future work. The Technical Paper uses the standard uncertainty
language of the Fourth Assessment (see Box 1.1).
Box 1.1: Uncertainties in current knowledge: their treatment in the Technical Paper [SYR]
The IPCC Uncertainty Guidance Note9 defines a framework for the treatment of uncertainties across all Working Groups
and in this Technical Paper. This framework is broad because the Working Groups assess material from different disciplines
and cover a diversity of approaches to the treatment of uncertainty drawn from the literature. The nature of data, indicators
and analyses used in the natural sciences is generally different from that used in assessing technology development or in
the social sciences. WGI focuses on the former, WGIII on the latter, and WGII covers aspects of both.
Three different approaches are used to describe uncertainties, each with a distinct form of language. Choices among and
within these three approaches depend on both the nature of the information available and the authors’ expert judgement
of the correctness and completeness of current scientific understanding.
Where uncertainty is assessed qualitatively, it is characterised by providing a relative sense of the amount and quality
of evidence (that is, information from theory, observations or models, indicating whether a belief or proposition is true or
valid) and the degree of agreement (that is, the level of concurrence in the literature on a particular finding). This approach
is used by WGIII through a series of self-explanatory terms such as: high agreement, much evidence; high agreement,
medium evidence; medium agreement, medium evidence; etc.
Where uncertainty is assessed more quantitatively using expert judgement of the correctness of the underlying data,
models or analyses, then the following scale of confidence levels is used to express the assessed chance of a finding
being correct: very high confidence at least 9 out of 10; high confidence about 8 out of 10; medium confidence about 5 out
of 10; low confidence about 2 out of 10; and very low confidence less than 1 out of 10.
Where uncertainty in specific outcomes is assessed using expert judgement and statistical analysis of a body of evidence
(e.g., observations or model results), then the following likelihood ranges are used to express the assessed probability of
occurrence: virtually certain >99%; extremely likely >95%; very likely >90%; likely >66%; more likely than not >50%; about
as likely as not 33% to 66%; unlikely <33%; very unlikely <10%; extremely unlikely <5%; exceptionally unlikely <1%.
WGII has used a combination of confidence and likelihood assessments, and WGI has predominantly used likelihood
assessments.
This Technical Paper follows the uncertainty assessment of the underlying Working Groups. Where synthesised findings
are based on information from more than one Working Group, the description of uncertainty used is consistent with that
for the components drawn from the respective Reports.
9
See http://www.ipcc.ch/meetings/ar4-workshops-express-meetings/uncertainty-guidance-note.pdf.
11
2
Observed and projected changes in
climate as they relate to water
Section 2
Observed and projected changes in climate as they relate to water
Water is involved in all components of the climate system
(atmosphere, hydrosphere, cryosphere, land surface and
biosphere). Therefore, climate change affects water through a
number of mechanisms. This section discusses observations of
recent changes in water-related variables, and projections of
future changes.
2.1 Observed changes in climate as they
iiiiiiirelate to water
The hydrological cycle is intimately linked with changes in
atmospheric temperature and radiation balance. Warming of
the climate system in recent decades is unequivocal, as is now
evident from observations of increases in global average air
and ocean temperatures, widespread melting of snow and ice,
and rising global sea level. Net anthropogenic radiative forcing
of the climate is estimated to be positive (warming effect),
with a best estimate of 1.6 Wm−2 for 2005 (relative to 1750
pre-industrial values). The best-estimate linear trend in global
surface temperature from 1906 to 2005 is a warming of 0.74°C
(likely range 0.56 to 0.92°C), with a more rapid warming trend
over the past 50 years. New analyses show warming rates in
the lower- and mid-troposphere that are similar to rates at the
surface. Attribution studies show that most of the observed
increase in global temperatures since the mid-20th century
is very likely due to the observed increase in anthropogenic
greenhouse gas concentrations. At the continental scale, it is
likely that there has been significant anthropogenic warming
over the past 50 years averaged over each of the continents
except Antarctica. For widespread regions, cold days, cold
nights and frost have become less frequent, while hot days, hot
nights and heatwaves have become more frequent over the past
50 years. [WGI SPM]
Climate warming observed over the past several decades is
consistently associated with changes in a number of components
of the hydrological cycle and hydrological systems such
as: changing precipitation patterns, intensity and extremes;
widespread melting of snow and ice; increasing atmospheric
water vapour; increasing evaporation; and changes in soil
moisture and runoff. There is significant natural variability – on
interannual to decadal time-scales – in all components of the
hydrological cycle, often masking long-term trends. There is
still substantial uncertainty in trends of hydrological variables
because of large regional differences, and because of limitations
in the spatial and temporal coverage of monitoring networks
(Huntington, 2006). At present, documenting interannual
variations and trends in precipitation over the oceans remains
a challenge. [WGI 3.3]
Understanding and attribution of observed changes also presents
a challenge. For hydrological variables such as runoff, nonclimate-related factors may play an important role locally (e.g.,
changes in extraction). The climate response to forcing agents
is also complex. For example, one effect of absorbing aerosols
(e.g., black carbon) is to intercept heat in the aerosol layer
which would otherwise reach the surface, driving evaporation
and subsequent latent heat release above the surface. Hence,
absorbing aerosols may locally reduce evaporation and
precipitation. Many aerosol processes are omitted or included
in somewhat simple ways in climate models, and the local
magnitude of their effects on precipitation is in some cases
poorly known. Despite the above uncertainties, a number
of statements can be made on the attribution of observed
hydrological changes, and these are included in the discussion
of individual variables in this section, based on the assessments
in AR4. [WGI 3.3, 7.5.2, 8.2.1, 8.2.5, 9.5.4; WGII 3.1, 3.2]
2.1.1
Precipitation (including extremes) and
water vapour
Trends in land precipitation have been analysed using a number
of data sets; notably the Global Historical Climatology Network
(GHCN: Peterson and Vose, 1997), but also the Precipitation
Reconstruction over Land (PREC/L: Chen et al., 2002), the
Global Precipitation Climatology Project (GPCP: Adler et al.,
2003), the Global Precipitation Climatology Centre (GPCC:
Beck et al., 2005) and the Climatic Research Unit (CRU:
Mitchell and Jones, 2005). Precipitation over land generally
increased over the 20th century between 30°N and 85°N,
but notable decreases have occurred in the past 30–40 years
from 10°S to 30°N (Figure 2.1). Salinity decreases in the
North Atlantic and south of 25°S suggest similar precipitation
changes over the ocean. From 10°N to 30°N, precipitation
increased markedly from 1900 to the 1950s, but declined after
about 1970. There are no strong hemispheric-scale trends over
Southern Hemisphere extra-tropical land masses. At the time
of writing, the attribution of changes in global precipitation is
uncertain, since precipitation is strongly influenced by largescale patterns of natural variability. [WGI 3.3.2.1]
The linear trend for the global average from GHCN during
1901–2005 is statistically insignificant (Figure 2.2). None of
the trend estimates for 1951–2005 are significant, with many
discrepancies between data sets, demonstrating the difficulty
of monitoring a quantity such as precipitation, which has large
variability in both space and time. Global changes are not linear
in time, showing significant decadal variability, with a relatively
wet period from the 1950s to the 1970s, followed by a decline
in precipitation. Global averages are dominated by tropical and
sub-tropical precipitation. [WGI 3.3.2.1]
Spatial patterns of trends in annual precipitation are shown in
Figure 2.3, using GHCN station data interpolated to a 5° × 5°
latitude/longitude grid. Over much of North America and
Eurasia, annual precipitation has increased during the 105 years
from 1901, consistent with Figure 2.1. The period since 1979
shows a more complex pattern, with regional drying evident
(e.g., south-west North America). Over most of Eurasia, the
number of grid-boxes showing increases in precipitation is
greater than the number showing decreases, for both periods.
There is a tendency for inverse variations between northern
Europe and the Mediterranean, associated with changes in the
North Atlantic Oscillation teleconnection (see also Section
2.1.7). [WGI 3.3.2.2]
15
Observed and projected changes in climate as they relate to water
Section 2
The largest negative trends since 1901 in annual precipitation
are observed over western Africa and the Sahel (see also Section
5.1), although there were downward trends in many other parts
of Africa, and in south Asia. Since 1979, precipitation has
increased in the Sahel region and in other parts of tropical Africa,
related in part to variations associated with teleconnection
patterns (see also Section 2.1.7). Over much of north-western
India the 1901–2005 period shows increases of more than 20%
per century`, but the same area shows a strong decrease in
annual precipitation since 1979. North-western Australia shows
areas with moderate to strong increases in annual precipitation
over both periods. Conditions have become wetter over northwest Australia, but there has been a marked downward trend in
the far south-west, characterised by a downward shift around
1975. [WGI 3.3.2.2]
Figure 2.1: Latitude–time section of average annual
anomalies for precipitation (%) over land from 1900
to 2005, relative to their 1961–1990 means. Values are
averaged across all longitudes and are smoothed with a
filter to remove fluctuations less than about 6 years. The
colour scale is non-linear and grey areas indicate missing
data. [WGI Figure 3.15]
Figure 2.2: Time-series for 1900–2005 of annual global land
precipitation anomalies (mm) from GHCN with respect to
the 1981–2000 base period. Smoothed decadal-scale values
are also given for the GHCN, PREC/L, GPCP, GPCC and
CRU data sets. [WGI Figure 3.12]
Across South America, increasingly wet conditions have been
observed over the Amazon Basin and south-eastern South
America, including Patagonia, while negative trends in annual
precipitation have been observed over Chile and parts of the
western coast of the continent. Variations over Amazonia,
Central America and western North America are suggestive of
latitudinal changes in monsoon features. [WGI 3.3.2.2]
16
A number of model studies suggest that changes in radiative
forcing (from combined anthropogenic, volcanic and solar
sources) have played a part in observed trends in mean
precipitation. However, climate models appear to underestimate
the variance of land mean precipitation compared to
observational estimates. It is not clear whether this discrepancy
results from an underestimated response to shortwave forcing,
underestimated internal climate variability, observational errors,
or some combination of these. Theoretical considerations
suggest that the influence of increasing greenhouse gases on
mean precipitation may be difficult to detect. [WGI 9.5.4]
Widespread increases in heavy precipitation events (e.g., above
the 95th percentile) have been observed, even in places where
total amounts have decreased. These increases are associated
with increased atmospheric water vapour and are consistent with
observed warming (Figure 2.4). However, rainfall statistics are
dominated by interannual to decadal-scale variations, and trend
estimates are spatially incoherent (e.g., Peterson et al., 2002;
Griffiths et al., 2003; Herath and Ratnayake, 2004). Moreover,
only a few regions have data series of sufficient quality and
length to assess trends in extremes reliably. Statistically
significant increases in the occurrence of heavy precipitation
have been observed across Europe and North America (Klein
Tank and Können, 2003; Kunkel et al., 2003; Groisman et al.,
2004; Haylock and Goodess, 2004). Seasonality of changes
varies with location: increases are strongest in the warm season
in the USA, while in Europe changes were most notable in the
cool season (Groisman et al., 2004; Haylock and Goodess,
2004). Further discussion of regional changes is presented in
Section 5. [WGI 3.8.2.2]
Theoretical and climate model studies suggest that, in a climate
that is warming due to increasing greenhouse gases, a greater
increase is expected in extreme precipitation, as compared to
the mean. Hence, anthropogenic influence may be easier to
detect in extreme precipitation than in the mean. This is because
extreme precipitation is controlled by the availability of water
vapour, while mean precipitation is controlled by the ability of
the atmosphere to radiate long-wave energy (released as latent
heat by condensation) to space, and the latter is restricted by
increasing greenhouse gases. Taken together, the observational
Section 2
Observed and projected changes in climate as they relate to water
Figure 2.3: Trend of annual precipitation amounts, 1901–2005 (upper, % per century) and 1979–2005 (lower, % per decade), as
a percentage of the 1961–1990 average, from GHCN station data. Grey areas have insufficient data to produce reliable trends.
[WGI Figure 3.13]
and modelling studies lead to an overall conclusion that an
increase in the frequency of heavy precipitation events (or in
the proportion of total rainfall from heavy falls) is likely to have
occurred over most land areas over the late 20th century, and
that this trend is more likely than not to include an anthropogenic
contribution. The magnitude of the anthropogenic contribution
cannot be assessed at this stage. [WGI SPM, 9.5.4, 10.3.6,
FAQ10.1]
There is observational evidence for an increase in intense
tropical cyclone activity in the North Atlantic since about 1970,
correlated with increases in tropical sea surface temperatures
(SSTs). There are also suggestions of increased intense tropical
cyclone activity in some other regions, but in these regions
concerns over data quality are greater. Multi-decadal variability
and the quality of the tropical cyclone records prior to routine
satellite observations in about 1970 complicate the detection of
17
Observed and projected changes in climate as they relate to water
Section 2
Figure 2.4: Upper panel shows observed trends (% per decade) for 1951–2003 in the contribution to total annual
precipitation from very wet days (95th percentile and above). Middle panel shows, for global annual precipitation, the
change in the contribution of very wet days to the total (%, compared to the 1961–1990 average of 22.5%) (after Alexander
et al., 2006). Lower panel shows regions where disproportionate changes in heavy and very heavy precipitation were
documented as either an increase (+) or decrease (−) compared to the change in annual and/or seasonal precipitation
(updated from Groisman et al., 2005). [WGI Figure 3.39]
long-term trends in tropical cyclone activity. There is no clear
trend in the annual numbers of tropical cyclones. Anthropogenic
factors have more likely than not contributed to observed
increases in intense tropical cyclone activity. However, the
apparent increase in the proportion of very intense storms since
1970 in some regions is much larger than simulated by current
models for that period. [WGI SPM]
The water vapour content of the troposphere has been observed
to increase in recent decades, consistent with observed warming
18
and near-constant relative humidity. Total column water vapour
has increased over the global oceans by 1.2 ± 0.3% per decade
from 1988 to 2004, in a pattern consistent with changes in sea
surface temperature. Many studies show increases in nearsurface atmospheric moisture, but there are regional differences
and differences between day and night. As with other
components of the hydrological cycle, interannual to decadalscale variations are substantial, but a significant upward trend
has been observed over the global oceans and over some land
areas in the Northern Hemisphere. Since observed warming
Observed and projected changes in climate as they relate to water
Section 2
of SST is likely to be largely anthropogenic, this suggests that
anthropogenic influence has contributed to the observed increase
in atmospheric water vapour over the oceans. However, at the
time of writing of the AR4, no formal attribution study was
available. [WGI 3.4.2, 9.5.4]
2.1.2
Snow and land ice
The cryosphere (consisting of snow, ice and frozen ground) on
land stores about 75% of the world’s freshwater. In the climate
system, the cryosphere and its changes are intricately linked to
the surface energy budget, the water cycle and sea-level change.
More than one-sixth of the world’s population lives in glacieror snowmelt-fed river basins (Stern, 2007). [WGII 3.4.1] Figure
2.5 shows cryosphere trends, indicating significant decreases in
ice storage in many components. [WGI Chapter 4]
2.1.2.1
Snow cover, frozen ground, lake and river ice
Snow cover has decreased in most regions, especially in spring
and summer. Northern Hemisphere snow cover observed by
satellites over the 1966–2005 period decreased in every month
except November and December, with a stepwise drop of 5% in
the annual mean in the late 1980s. Declines in the mountains of
western North America and in the Swiss Alps have been largest
at lower elevations. In the Southern Hemisphere, the few long
records or proxies available mostly show either decreases or no
change in the past 40 years or more. [WGI 4.2.2]
Degradation of permafrost and seasonally frozen ground is
leading to changes in land surface characteristics and drainage
systems. Seasonally frozen ground includes both seasonal soil
freeze–thaw in non-permafrost regions and the active layer
over permafrost that thaws in summer and freezes in winter.
The estimated maximum extent of seasonally frozen ground
in non-permafrost areas has decreased by about 7% in the
Northern Hemisphere from 1901 to 2002, with a decrease of up
to 15% in spring. Its maximum depth has decreased by about
0.3 m in Eurasia since the mid-20th century in response to
winter warming and increases in snow depth. Over the period
1956 to 1990, the active layer measured at 31 stations in Russia
exhibited a statistically significant deepening of about 21 cm.
Records from other regions are too short for trend analyses.
Temperature at the top of the permafrost layer has increased
by up to 3°C since the 1980s in the Arctic. Permafrost warming
and degradation of frozen ground appear to be the result of
increased summer air temperatures and changes in the depth
and duration of snow cover. [WGI 4.7, Chapter 9]
Freeze-up and break-up dates for river and lake ice exhibit
considerable spatial variability. Averaged over available data
for the Northern Hemisphere spanning the past 150 years,
freeze-up has been delayed at a rate of 5.8 ± 1.6 days per
century, while the break-up date has occurred earlier at a rate of
6.5 ± 1.2 days per century. There are insufficient published data
on river and lake ice thickness to allow the assessment of trends.
Modelling studies (e.g., Duguay et al., 2003) indicate that much
of the variability in maximum ice thickness and break-up date
is driven by variations in snowfall. [WGI 4.3]
Figure 2.5: Anomaly time-series (departure from the longterm mean) of polar surface air temperature (A and E),
Northern Hemisphere (NH) seasonally frozen ground extent
(B), NH snow cover extent for March–April (C), and global
glacier mass balance (D). The solid red line in D denotes the
cumulative global glacier mass balance; otherwise it represents
the smoothed time-series. [Adapted from WGI FAQ 4.1]
2.1.2.2
Glaciers and ice caps
On average, glaciers and ice caps in the Northern Hemisphere
and Patagonia show a moderate but rather consistent
increase in mass turnover over the last half-century, and
substantially increased melting. [WGI 4.5.2, 4.6.2.2.1] As
a result, considerable mass loss occurred on the majority of
glaciers and ice caps worldwide (Figure 2.6) with increasing
rates: from 1960/61 to 1989/90 the loss was 136 ± 57 Gt/yr
(0.37 ± 0.16 mm/yr sea-level equivalent, SLE), and between
1990/91 and 2003/04 it was 280 ± 79 Gt/yr (0.77 ± 0.22 mm/yr
SLE). The widespread 20th-century shrinkage appears to imply
widespread warming as the primary cause although, in the
tropics, changes in atmospheric moisture might be contributing.
There is evidence that this melting has very likely contributed to
observed sea-level rise. [WGI 4.5 Table 4.4, 9.5]
19
Section 2
Observed and projected changes in climate as they relate to water
Figure 2.6: Cumulative mean specific mass balances (a) and cumulative total mass balances (b) of glaciers and ice caps,
calculated for large regions (Dyurgerov and Meier, 2005). The mass balance of a glacier is the sum of all mass gains and
losses during a hydrological year. Mean specific mass balance is the total mass balance divided by the total surface area of all
glaciers and ice caps of a region, and it shows the strength of change in the respective region. Total mass balance is presented
as the contribution from each region to sea-level rise. [WGI 4.5.2, Figure 4.15]
Formation of lakes is occurring as glacier tongues retreat from
prominent Little Ice Age (LIA) moraines in several steep
mountain ranges, including the Himalayas, the Andes, and the
Alps. These lakes have a high potential for glacial lake outburst
floods. [WGII 1.3.1.1, Table 1.2]
2.1.3
Sea level
Global mean sea level has been rising and there is high confidence
that the rate of rise has increased between the mid-19th and
the mid-20th centuries. The average rate was 1.7 ± 0.5 mm/
yr for the 20th century, 1.8 ± 0.5 mm/yr for 1961–2003, and
3.1 ± 0.7 mm/yr for 1993–2003. It is not known whether the
higher rate in 1993–2003 is due to decadal variability or to an
increase in the longer-term trend. Spatially, the change is highly
non-uniform; e.g., over the period 1993 to 2003, rates in some
regions were up to several times the global mean rise while, in
other regions, sea levels fell. [WGI 5.ES]
There are uncertainties in the estimates of the contributions to
the long-term sea-level change. For the period 1993–2003, the
contributions from thermal expansion (1.6 ± 0.5 mm/yr), mass
loss from glaciers and ice caps (0.77 ± 0.22 mm/yr) and mass
loss from the Greenland (0.21 ± 0.07 mm/yr) and Antarctic
(0.21 ± 0.35 mm/yr) ice sheets totalled 2.8 ± 0.7 mm/yr. For
this period, the sum of these climate contributions is consistent
with the directly observed sea-level rise given above, within
20
the observational uncertainties. For the longer period 1961–
2003, the sum of the climate contributions is estimated to be
smaller than the observed total sea-level rise; however, the
observing system was less reliable prior to 1993. For both
periods, the estimated contributions from thermal expansion
and from glaciers/ice caps are larger than the contributions
from the Greenland and Antarctic ice sheets. The large error
bars for Antarctica mean that it is uncertain whether Antarctica
has contributed positively or negatively to sea level. Increases
in sea level are consistent with warming, and modelling
studies suggest that overall it is very likely that the response
to anthropogenic forcing contributed to sea-level rise during
the latter half of the 20th century; however, the observational
uncertainties, combined with a lack of suitable studies, mean
that it is difficult to quantify the anthropogenic contribution.
[WGI SPM, 5.5, 9.5.2]
Rising sea level potentially affects coastal regions, but
attribution is not always clear. Global increases in extreme high
water levels since 1975 are related to both mean sea-level rise
and large-scale inter-decadal climate variability (Woodworth
and Blackman, 2004). [WGII 1.3.3]
2.1.4
Evapotranspiration
There are very limited direct measurements of actual
evapotranspiration over global land areas, while global
Section 2
Observed and projected changes in climate as they relate to water
analysis products10 are sensitive to the type of analysis and
can contain large errors, and thus are not suitable for trend
analysis. Therefore, there is little literature on observed trends
in evapotranspiration, whether actual or potential. [WGI 3.3.3]
2005; Semenov et al., 2006) and a major part of North America
(Robeson, 2002; Feng and Hu, 2004). [WGII 1.3.6.1]
2.1.4.1
Pan evaporation
Decreasing trends during recent decades are found in sparse
records of pan evaporation (measured evaporation from an open
water surface in a pan, a proxy for potential evapotranspiration)
over the USA (Peterson et al., 1995; Golubev et al., 2001; Hobbins
et al., 2004), India (Chattopadhyay and Hulme, 1997), Australia
(Roderick and Farquhar, 2004), New Zealand (Roderick and
Farquhar, 2005), China (Liu et al., 2004; Qian et al., 2006b)
and Thailand (Tebakari et al., 2005). Pan measurements do not
represent actual evaporation (Brutsaert and Parlange, 1998),
and trends may be caused by decreasing surface solar radiation
(over the USA and parts of Europe and Russia) and decreased
sunshine duration over China that may be related to increases
in air pollution and atmospheric aerosols and increases in cloud
cover. [WGI 3.3.3, Box 3.2]
Historical records of soil moisture content measured in situ
are available for only a few regions and are often very short
in duration. [WGI 3.3.4] Among more than 600 stations from
a large variety of climates, Robock et al. (2000) identified an
increasing long-term trend in surface (top 1 m) soil moisture
content during summer for the stations with the longest records,
mostly located in the former Soviet Union, China, and central
USA. The longest records available, from the Ukraine, show
overall increases in surface soil moisture, although increases
are less marked in recent decades (Robock et al., 2005). The
initial approach to estimating soil moisture has been to calculate
Palmer Drought Severity Index (PDSI) values from observed
precipitation and temperature. PDSI changes are discussed in
Section 3.1.2.4. [WGI Box 3.1, 3.3.4]
2.1.4.2
Actual evapotranspiration
The TAR reported that actual evapotranspiration increased
during the second half of the 20th century over most dry
regions of the USA and Russia (Golubev et al., 2001), resulting
from greater availability of surface moisture due to increased
precipitation and larger atmospheric moisture demand due
to higher temperature. Using observations of precipitation,
temperature, cloudiness-based surface solar radiation and a
comprehensive land surface model, Qian et al. (2006a) found
that global land evapotranspiration closely follows variations
in land precipitation. Global precipitation values peaked in the
early 1970s and then decreased somewhat, but reflect mainly
tropical values, and precipitation has increased more generally
over land at higher latitudes. Changes in evapotranspiration
depend not only on moisture supply but also on energy
availability and surface wind. [WGI 3.3.3]
Other factors affecting actual evapotranspiration include
the direct effects of atmospheric CO2 enrichment on plant
physiology. The literature on these direct effects, with respect
to observed evapotranspiration trends, is non-existent, although
effects on runoff have been seen. [WGI 9.5.4]
Annual amounts of evapotranspiration depend, in part, on the
length of the growing season. The AR4 presents evidence for
observed increases in growing season length. These increases,
associated with earlier last spring frost and delayed autumn
frost dates, are clearly apparent in temperate regions of Eurasia
(Moonen et al., 2002; Menzel et al., 2003; Genovese et al.,
10
2.1.5
2.1.6
Soil moisture
Runoff and river discharge
A large number of studies have examined potential trends
in measures of river discharge during the 20th century, at
scales ranging from catchment to global. Some have detected
significant trends in some indicators of flow, and some have
demonstrated statistically significant links with trends in
temperature or precipitation. Many studies, however, have
found no trends or have been unable to separate out the effects
of variations in temperature and precipitation from the effects
of human interventions in the catchment. The methodology
used to search for trends can also influence results. For
example, different statistical tests can give different indications
of significance; different periods of record (particularly start
and end dates) can suggest different rates of change; failing
to allow for cross-correlation between catchments can lead
to an overestimation of the numbers of catchments showing
significant change. Another limitation of trend analysis is the
availability of consistent, quality-controlled data. Available
streamflow gauge records cover only about two-thirds of the
global actively drained land area and often contain gaps and
vary in record length (Dai and Trenberth, 2002). Finally, human
interventions have affected flow regimes in many catchments.
[WGI 3.3.4, 9.1, 9.5.1; WGII 1.3.2]
At the global scale, there is evidence of a broadly coherent pattern
of change in annual runoff, with some regions experiencing an
increase in runoff (e.g., high latitudes and large parts of the
USA) and others (such as parts of West Africa, southern Europe
and southernmost South America) experiencing a decrease in
‘Analysis products’ refers to estimates of past climate variations produced by assimilating a range of observations into a weather forecasting or
climate model, in the way that is done routinely to initialise daily weather forecasts. Because operational weather analysis/forecasting systems
are developed over time, a number of ‘reanalysis’ exercises have been carried out in which the available observations are assimilated into a single
system, eliminating any spurious jumps or trends due to changes in the underlying system. An advantage of analysis systems is that they produce
global fields that include many quantities that are not directly observed. A potential disadvantage is that all fields are a mixture of observations
and models, and for regions/variables for which there are few observations, may represent largely the climatology of the underlying model.
21
Observed and projected changes in climate as they relate to water
runoff (Milly et al., 2005, and many catchment-scale studies).
Variations in flow from year to year are also influenced in many
parts of the world by large-scale climatic patterns associated,
for example, with ENSO, the NAO and the PNA pattern.11 One
study (Labat et al., 2004) claimed a 4% increase in global total
runoff per 1°C rise in temperature during the 20th century, with
regional variations around this trend, but debate around this
conclusion (Labat et al., 2004; Legates et al., 2005) has focused
on the effects of non-climatic drivers on runoff and the influence
of a small number of data points on the results. Gedney et al.
(2006) attributed widespread increases in runoff during the
20th century largely to the suppression of evapotranspiration
by increasing CO2 concentrations (which affect stomatal
conductance), although other evidence for such a relationship
is difficult to find and Section 2.1.4 presents evidence for an
increase in evapotranspiration. [WGII 1.3.2]
Trends in runoff are not always consistent with changes in
precipitation. This may be due to data limitations (in particular
the coverage of precipitation data), the effect of human
interventions such as reservoir impoundment (as is the case with
the major Eurasian rivers), or the competing effects of changes
in precipitation and temperature (as in Sweden: see Lindstrom
and Bergstrom, 2004).
There is, however, far more robust and widespread evidence
that the timing of river flows in many regions where winter
precipitation falls as snow has been significantly altered. Higher
temperatures mean that a greater proportion of the winter
precipitation falls as rain rather than snow, and the snowmelt
season begins earlier. Snowmelt in parts of New England shifted
forward by 1 to 2 weeks between 1936 and 2000 (Hodgkins
et al., 2003), although this has had little discernible effect on
summer flows (Hodgkins et al., 2005). [WGII 1.3.2]
2.1.7
Patterns of large-scale variability
The climate system has a number of preferred patterns of
variability having a direct influence on elements of the
hydrological cycle. Regional climates may vary out of phase,
owing to the action of such ‘teleconnections’. Teleconnections
are often associated with droughts and floods, and with other
changes which have significant impacts on humans. A brief
overview is given below of the key teleconnection patterns. A more
complete discussion is given in Section 3.6 of the WGI AR4.
A teleconnection is defined by a spatial pattern and a timeseries describing variations in its magnitude and phase. Spatial
patterns may be defined over a grid or by indices based on
station observations. For example, the Southern Oscillation
Index (SOI) is based solely on differences in mean sea-level
pressure anomalies between Tahiti (eastern Pacific) and Darwin
(western Pacific), yet it captures much of the variability of
large-scale atmospheric circulation throughout the tropical
Pacific. Teleconnection patterns tend to be most prominent in
winter (especially in the Northern Hemisphere), when the mean
11
Section 2
circulation is strongest. The strength of teleconnections, and the
way in which they influence surface climate, also varies over
long time-scales. [WGI 3.6.1]
The SOI describes the atmospheric component of the El
Niño–Southern Oscillation (ENSO), the most significant mode
of interannual variability of the global climate. ENSO has
global impacts on atmospheric circulation, precipitation and
temperature (Trenberth and Caron, 2000). ENSO is associated
with an east–west shift in tropical Pacific precipitation, and with
modulation of the main tropical convergence zones. ENSO is
also associated with wave-like disturbances to the atmospheric
circulation outside the tropics, such as the Pacific–North
American (PNA) and Pacific–South American (PSA) patterns,
which have major regional climate effects. The strength
and frequency of ENSO events vary on the decadal scale, in
association with the Pacific Decadal Oscillation (PDO, also
known as the Inter-decadal Pacific Oscillation or IPO), which
modulates the mean state of ocean surface temperatures and
the tropical atmospheric circulation on time-scales of 20 years
and longer. The climate shift in 1976/77 (Trenberth, 1990) was
associated with changes in El Niño evolution (Trenberth and
Stepaniak, 2001) and a tendency towards more prolonged and
stronger El Niños. As yet there is no formally detectable change
in ENSO variability in observations. [WGI 3.6.2, 3.6.3]
Outside the tropics, variability of the atmospheric circulation
on time-scales of a month or longer is dominated by variations
in the strength and locations of the jet streams and associated
storm tracks, characterised by the Northern and Southern
‘Annular Modes’ (NAM and SAM, respectively: Quadrelli and
Wallace, 2004; Trenberth et al., 2005). The NAM is closely
related to the North Atlantic Oscillation (NAO), although
the latter is most strongly associated with the Atlantic storm
track and with climate variations over Europe. The NAO is
characterised by out-of-phase pressure anomalies between
temperate and high latitudes over the Atlantic sector. The
NAO has its strongest signature in winter, when its positive
(negative) phase exhibits an enhanced (diminished) Iceland
Low and Azores High (Hurrell et al., 2003). The closely related
NAM has a similar structure over the Atlantic, but is more
longitudinally symmetrical. The NAO has a strong influence on
wintertime surface temperatures across much of the Northern
Hemisphere, and on storminess and precipitation over Europe
and North Africa, with a poleward shift in precipitation in the
positive phase and an Equatorward shift in the negative phase.
There is evidence of prolonged positive and negative NAO
periods during the last few centuries (Cook et al., 2002; Jones
et al., 2003a). In winter, a reversal occurred from the minimum
index values in the late 1960s to strongly positive NAO index
values in the mid-1990s. Since then, NAO values have declined
to near their long-term mean. Attribution studies suggest that
the trend over recent decades in the NAM is likely to be related
in part to human activity. However, the response to natural and
anthropogenic forcings that is simulated by climate models is
smaller than the observed trend. [WGI 3.6.4, 9.ES]
Respectively, ENSO = El Niño–Southern Oscillation, NAO = North Atlantic Oscillation, PNA = Pacific–North American; see Section 2.1.7 and
Glossary for further explanation.
22
Section 2
Observed and projected changes in climate as they relate to water
The Southern Annular Mode (SAM) is associated with
synchronous pressure variations of opposite sign in mid- and
high latitudes, reflecting changes in the main belt of sub-polar
westerly winds. Enhanced Southern Ocean westerlies occur in
the positive phase of the SAM, which has become more common
in recent decades, leading to more cyclones in the circumpolar
trough (Sinclair et al., 1997), a poleward shift in precipitation,
and a greater contribution to Antarctic precipitation (Noone
and Simmonds, 2002). The SAM also affects spatial patterns
of precipitation variability in Antarctica (Genthon et al., 2003)
and southern South America (Silvestri and Vera, 2003). Model
simulations suggest that the recent trend in the SAM has been
affected by increased greenhouse gas concentration and, in
particular, by stratospheric ozone depletion. [WGI 3.6.5,
9.5.3.3]
2.2.1
North Atlantic SSTs show about a 70-year variation during the
instrumental period (and in proxy reconstructions), termed the
Atlantic Multi-decadal Oscillation (AMO: Kerr, 2000). A warm
phase occurred during 1930–1960 and cool phases during 1905–
1925 and 1970–1990 (Schlesinger and Ramankutty, 1994). The
AMO appears to have returned to a warm phase beginning in the
mid-1990s. The AMO may be related to changes in the strength
of the thermohaline circulation (Delworth and Mann, 2000; Latif,
2001; Sutton and Hodson, 2003; Knight et al., 2005). The AMO
has been linked to multi-year precipitation anomalies over North
America, appears to modulate ENSO teleconnections (Enfield et
al., 2001; McCabe et al., 2004; Shabbar and Skinner, 2004) and
also plays a role in Atlantic hurricane formation (Goldenberg et
al., 2001). The AMO is believed to be a driver of multi-decadal
variations in Sahel drought, precipitation in the Caribbean,
summertime climate of both North America and Europe, sea-ice
concentration in the Greenland Sea, and sea-level pressure over
the southern USA, the North Atlantic and southern Europe (e.g.,
Venegas and Mysak, 2000; Goldenberg et al., 2001; Sutton and
Hodson, 2005; Trenberth and Shea, 2006). [WGI 3.6.6]
The impacts of deforestation on climate illustrate this complexity.
Some studies indicate that deforestation could lead to reduced
daytime temperatures and increases in boundary layer cloud as a
consequence of rising albedo, transpiration and latent heat loss.
However, these effects are dependent on the properties of both
the replacement vegetation and the underlying soil/snow surface
– and in some cases the opposite effects have been suggested. The
effects of deforestation on precipitation are likewise complex,
with both negative and positive impacts being found, dependent
on land surface and vegetation characteristics. [WGI 7.2, 7.5]
2.2 Influences and feedbacks of
iiiiiiihydrological changes on climate
Some robust correlations have been observed between
temperature and precipitation in many regions. This provides
evidence that processes controlling the hydrological cycle and
temperature are closely coupled. At a global scale, changes in
water vapour, clouds and ice change the radiation balance of the
Earth and hence play a major role in determining the climate
response to increasing greenhouse gases. The global impact of
these processes on temperature response is discussed in WGI
AR4 Section 8.6. In this section, we discuss some processes
through which changes in hydrological variables can produce
feedback effects on regional climate, or on the atmospheric
budget of major greenhouse gases. The purpose of this section
is not to provide a comprehensive discussion of such processes,
but to illustrate the tight coupling of hydrological processes to
the rest of the climate system. [WGI 3.3.5, Chapter 7, 8.6]
Land surface effects
Surface water balances reflect the availability of both water
and energy. In regions where water availability is high,
evapotranspiration is controlled by the properties of both
the atmospheric boundary layer and surface vegetation cover.
Changes in the surface water balance can feed back on the
climate system by recycling water into the boundary layer
(instead of allowing it to run off or penetrate to deep soil levels).
The sign and magnitude of such effects are often highly variable,
depending on the details of the local environment. Hence, while
in some cases these feedbacks may be relatively small on a global
scale, they may become extremely important at smaller spaceor time-scales, leading to regional/local changes in variability or
extremes. [WGI 7.2]
A number of studies have suggested that, in semi-arid regions such
as the Sahel, the presence of vegetation can enhance conditions
for its own growth by recycling soil water into the atmosphere,
from where it can be precipitated again. This can result in the
possibility of multiple equilibria for such regions, either with
or without precipitation and vegetation, and also suggests the
possibility of abrupt regime transitions, as may have happened
in the change from mid-Holocene to modern conditions. [WGI
Chapter 6, 7.2]
Soil moisture is a source of thermal inertia due to its heat capacity
and the latent heat required for evaporation. For this reason,
soil moisture has been proposed as an important control on,
for example, summer temperature and precipitation. Feedbacks
between soil moisture, precipitation and temperature are
particularly important in transition regions between dry and humid
areas, but the strength of the coupling between soil moisture and
precipitation varies by an order of magnitude between different
climate models, and observational constraints are not currently
available to narrow this uncertainty. [WGI 7.2, 8.2]
A further control on precipitation arises through stomatal closure
in response to increasing atmospheric CO2 concentrations. In
addition to its tendency to increase runoff through large-scale
decreases in total evapotranspiration (Section 2.3.4), this effect
may result in substantial reductions in precipitation in some
regions. [WGI 7.2]
Changes in snow cover as a result of regional warming feed back
on temperature through albedo changes. While the magnitude
23
Observed and projected changes in climate as they relate to water
of this feedback varies substantially between models, recent
studies suggest that the rate of spring snowmelt may provide
a good, observable estimate of this feedback strength, offering
the prospect of reduced uncertainty in future predictions of
temperature change in snow-covered regions. [WGI 8.6]
2.2.2
Feedbacks through changes in ocean
iiiiiiiiiiiiiiiicirculation
Freshwater input to the ocean changes the salinity, and hence
the density, of sea water. Thus, changes in the hydrological
cycle can change the density-driven (‘thermohaline’) ocean
circulation, and thence feed back on climate. A particular
example is the meridional overturning circulation (MOC) in the
North Atlantic Ocean. This circulation has a substantial impact
on surface temperature, precipitation and sea level in regions
around the North Atlantic and beyond. The Atlantic MOC is
projected to weaken during the 21st century, and this weakening
is important in modulating the overall climate change response.
In general, a weakening MOC is expected to moderate the
rate of warming at northern mid-latitudes, but some studies
suggest that it would also result in an increased rate of warming
in the Arctic. These responses also feed back on large-scale
precipitation through changes in evaporation from the low- and
mid-latitude Atlantic. While in many models the largest driver
of MOC weakening is surface warming (rather than freshening),
in the deep water source regions, hydrological changes do play
an important role, and uncertainty in the freshwater input is a
major contribution to the large inter-model spread in projections
of MOC response. Observed changes in ocean salinity over
recent decades are suggestive of changes in freshwater input.
While nearly all atmosphere–ocean general circulation model
(AOGCM) integrations show a weakening MOC in the 21st
century, none shows an abrupt transition to a different state.
Such an event is considered very unlikely in the 21st century,
but it is not possible to assess the likelihood of such events in
the longer term. [WGI 10.3.4]
Changes in precipitation, evaporation and runoff, and their
impact on the MOC, are explicitly modelled in current climate
projections. However, few climate models include a detailed
representation of changes in the mass balance of the Greenland
and Antarctic ice sheets, which represent a possible additional
source of freshwater to the ocean. The few studies available to
date that include detailed modelling of freshwater input from
Greenland do not suggest that this extra source will change the
broad conclusions presented above. [WGI 5.2, 8.7, 10.3, Box 10.1]
2.2.3
Emissions and sinks affected by
hydrological processes or biogeochemical
feedbacks
Changes in the hydrological cycle can feed back on climate
through changes in the atmospheric budgets of carbon dioxide,
methane and other radiatively-active chemical species, often
regulated by the biosphere. The processes involved are complex;
for example the response of heterotrophic soil respiration,
24
Section 2
a source of CO2, to increasing temperature depends strongly
on the amount of soil moisture. A new generation of climate
models, in which vegetation and the carbon cycle respond to
the changing climate, has allowed some of these processes to
be explored for the first time. All models suggest that there is a
positive feedback of climate change on the global carbon cycle,
resulting in a larger proportion of anthropogenic CO2 emissions
remaining in the atmosphere in a warmer climate. However,
the magnitude of the overall feedback varies substantially
between models; changes in net terrestrial primary productivity
are particularly uncertain, reflecting the underlying spread in
projections of regional precipitation change. [WGI 7.3]
A number of sources and sinks of methane are sensitive to
hydrological change, for example wetlands, permafrost,
rice agriculture (sources) and soil oxidation (sink). Other
active chemical species such as ozone have also been shown
to be sensitive to climate, again typically through complex
biogeochemical mechanisms. Atmospheric aerosol budgets
are directly sensitive to precipitation (e.g., through damping of
terrestrial dust sources and the importance of wet deposition
as a sink), and aerosols feed back onto precipitation by acting
as condensation nuclei and so influencing the precipitation
efficiency of clouds. The magnitude of these feedbacks remains
uncertain, and they are generally included only in simple ways,
if at all, in the current generation of climate models. [WGI 7.4]
2.3 Projected changes in climate as they
iiiiiiirelate to water
A major advance in climate change projections, compared
with those considered under the TAR, is the large number of
simulations available from a broader range of climate models,
run for various emissions scenarios. Best-estimate projections
from models indicate that decadal average warming over each
inhabited continent by 2030 is insensitive to the choice of SRES
scenario and is very likely to be at least twice as large (around
0.2°C per decade) as the corresponding model-estimated natural
variability during the 20th century. Continued greenhouse gas
emissions at or above current rates under SRES non-mitigation
scenarios would cause further warming and induce many
changes in the global climate system during the 21st century,
with these changes very likely to be larger than those observed
during the 20th century. Projected global average temperature
change for 2090–2099 (relative to 1980–1999), under the
SRES illustrative marker scenarios, ranges from 1.8°C (best
estimate, likely range 1.1°C to 2.9°C) for scenario B1, to 4.0°C
(best estimate, likely range 2.4°C to 6.4°C) for scenario A1FI.
Warming is projected to be greatest over land and at most high
northern latitudes, and least over the Southern Ocean and parts
of the North Atlantic Ocean. It is very likely that hot extremes
and heatwaves will continue to become more frequent.
[WGI SPM, Chapter 10]
Uncertainty in hydrological projections
Uncertainties in projected changes in the hydrological system
arise from internal variability of the climate system, uncertainty
Section 2
Observed and projected changes in climate as they relate to water
in future greenhouse gas and aerosol emissions, the translation
of these emissions into climate change by global climate models,
and hydrological model uncertainty. By the late 21st century,
under the A1B scenario, differences between climate model
precipitation projections are a larger source of uncertainty than
internal variability. This also implies that, in many cases, the
modelled changes in annual mean precipitation exceed the
(modelled) internal variability by this time. Projections become
less consistent between models as the spatial scale decreases.
[WGI 10.5.4.3] At high latitudes and in parts of the tropics, all
or nearly all models project an increase in precipitation, while in
some sub-tropical and lower mid-latitude regions precipitation
decreases in all or nearly all models. Between these areas of
robust increase and decrease, even the sign of precipitation
change is inconsistent across the current generation of models.
[WGI 10.3.2.3, 10.5.4.3] For other aspects of the hydrological
cycle, such as changes in evaporation, soil moisture and runoff,
the relative spread in projections is similar to, or larger than, the
changes in precipitation. [WGI 10.3.2.3]
Further sources of uncertainty in hydrological projections
arise from the structure of current climate models. Some
examples of processes that are, at best, only simply represented
in climate models are given in Section 2.2. Current models
generally exclude some feedbacks from vegetation change to
climate change. Most, although not all, of the simulations used
for deriving climate projections also exclude anthropogenic
changes in land cover. The treatment of anthropogenic aerosol
forcing is relatively simple in most climate models. While some
models include a wide range of anthropogenic aerosol species,
potentially important species, such as black carbon, are lacking
from most of the simulations used for the AR4 (see discussion
of the attribution of observed changes, in Section 2.1). More
than half of the AR4 models also exclude the indirect effects
of aerosols on clouds. The resolution of current climate models
also limits the proper representation of tropical cyclones and
heavy rainfall. [WGI 8.2.1, 8.2.2, 8.5.2, 8.5.3, 10.2.1]
Uncertainties arise from the incorporation of climate model
results into freshwater studies for two reasons: the different
spatial scales of global climate models and hydrological
models, and biases in the long-term mean precipitation as
computed by global climate models for the current climate.
A number of methods have been used to address the scale
differences, ranging from the simple interpolation of climate
model results to dynamic or statistical downscaling methods,
but all such methods introduce uncertainties into the projection.
Biases in simulated mean precipitation are often addressed by
adding modelled anomalies to the observed precipitation in
order to obtain the driving dataset for hydrological models.
Therefore, changes in interannual or day-to-day variability
of climate parameters are not taken into account in most
hydrological impact studies. This leads to an underestimation
of future floods, droughts and irrigation water requirements.
[WGII 3.3.1]
The uncertainties in climate change impacts on water resources,
droughts and floods arise for various reasons, such as different
scenarios of economic development, greenhouse gas emissions,
climate modelling and hydrological modelling. However, there
has not yet been a study that assesses how different hydrological
models react to the same climate change signal. [WGII 3.3.1]
Since the TAR, the uncertainty of climate model projections
for freshwater assessments is often taken into account by using
multi-model ensembles. Formal probabilistic assessments are
still rare. [WGII 3.3.1, 3.4]
Despite these uncertainties, some robust results are available. In
the sections that follow, uncertainties in projected changes are
discussed, based on the assessments in AR4.
2.3.1
Precipitation (including extremes) and
water vapour
2.3.1.1
Mean precipitation
Climate projections using multi-model ensembles show
increases in globally averaged mean water vapour, evaporation
and precipitation over the 21st century. The models suggest
that precipitation generally increases in the areas of regional
tropical precipitation maxima (such as the monsoon regimes,
and the tropical Pacific in particular) and at high latitudes, with
general decreases in the sub-tropics. [WGI SPM, 10.ES, 10.3.1,
10.3.2]
Increases in precipitation at high latitudes in both the winter
and summer seasons are highly consistent across models (see
Figure 2.7). Precipitation increases over the tropical oceans and
in some of the monsoon regimes, e.g., the south Asian monsoon
in summer (June to August) and the Australian monsoon in
summer (December to February), are notable and, while not
as consistent locally, considerable agreement is found at the
broader scale in the tropics. There are widespread decreases
in mid-latitude summer precipitation, except for increases in
eastern Asia. Decreases in precipitation over many sub-tropical
areas are evident in the multi-model ensemble mean, and
consistency in the sign of change among the models is often
high – particularly in some regions such as the tropical Central
American—Caribbean and the Mediterranean. [WGI 10.3.2]
Further discussion of regional changes is presented in Section 5.
The global distribution of the 2080–2099 change in annual mean
precipitation for the SRES A1B scenario is shown in Figure 2.8,
along with some other hydrological quantities from a 15-model
ensemble. Increases in annual precipitation exceeding 20%
occur in most high latitudes, as well as in eastern Africa, the
northern part of central Asia and the equatorial Pacific Ocean.
Substantial decreases of up to 20% occur in the Mediterranean
and Caribbean regions and on the sub-tropical western coasts of
each continent. Overall, precipitation over land increases some
5%, while precipitation over oceans increases 4%. The net
change over land accounts for 24% of the global mean increase
in precipitation. [WGI 10.3.2]
In climate model projections for the 21st century, global mean
evaporation changes closely balance global precipitation
change, but this relationship is not evident at the local scale
25
Observed and projected changes in climate as they relate to water
Section 2
Figure 2.7: Fifteen-model mean changes in precipitation (unit: mm/day) for DJF (left) and JJA (right). Changes are given
for the SRES A1B scenario, for the period 2080–2099 relative to 1980–1999. Stippling denotes areas where the magnitude of
the multi-model ensemble mean exceeds the inter-model standard deviation. [WGI Figure 10.9]
because of changes in the atmospheric transport of water vapour.
Annual average evaporation increases over much of the ocean,
with spatial variations tending to relate to variations in surface
warming. Atmospheric moisture convergence increases over
the equatorial oceans and over high latitudes. Over land, rainfall
changes tend to be balanced by both evaporation and runoff.
On global scales, the water vapour content of the atmosphere
is projected to increase in response to warmer temperatures,
with relative humidity remaining roughly constant. These
water vapour increases provide a positive feedback on climate
warming, since water vapour is a greenhouse gas. Associated
with this is a change in the vertical profile of atmospheric
temperature (‘lapse rate’), which partly offsets the positive
feedback. Recent evidence from models and observations
strongly supports a combined water vapour/lapse rate feedback
on climate of a strength comparable with that found in climate
general circulation models. [WGI 8.6, 10.ES, 10.3.2]
2.3.1.2
Precipitation extremes
It is very likely that heavy precipitation events will become
more frequent. Intensity of precipitation events is projected to
increase, particularly in tropical and high-latitude areas that
experience increases in mean precipitation. There is a tendency
for drying in mid-continental areas during summer, indicating
a greater risk of droughts in these regions. In most tropical and
mid- and high-latitude areas, extreme precipitation increases
more than mean precipitation. [WGI 10.3.5, 10.3.6]
A long-standing result from global coupled models noted in the
TAR was a projected increased likelihood of summer drying in
the mid-latitudes, with an associated increased risk of drought
(Figure 2.8). Fifteen recent AOGCM runs for a future warmer climate
indicate summer dryness in most parts of the northern sub-tropics and
mid-latitudes, but there is a large range in the amplitude of summer
dryness across models. Droughts associated with this summer
drying could result in regional vegetation die-off and contribute to
26
an increase in the percentage of land area experiencing drought
at any one time; for example, extreme drought increasing from
1% of present-day land area (by definition) to 30% by 2100
in the A2 scenario. Drier soil conditions can also contribute to
more severe heatwaves. [WGI 10.3.6]
Also associated with the risk of drying is a projected increase
in the risk of intense precipitation and flooding. Though
somewhat counter-intuitive, this is because precipitation is
projected to be concentrated in more intense events, with longer
periods of lower precipitation in between (see Section 2.1.1 for
further explanation). Therefore, intense and heavy episodic
rainfall events with high runoff amounts are interspersed with
longer relatively dry periods with increased evapotranspiration,
particularly in the sub-tropics. However, depending on the
threshold used to define such events, an increase in the
frequency of dry days does not necessarily mean a decrease in
the frequency of extreme high-rainfall events. Another aspect of
these changes has been related to changes in mean precipitation,
with wet extremes becoming more severe in many areas where
mean precipitation increases, and dry extremes becoming more
severe where mean precipitation decreases. [WGI 10.3.6]
Multi-model climate projections for the 21st century show
increases in both precipitation intensity and number of
consecutive dry days in many regions (Figure 2.9). Precipitation
intensity increases almost everywhere, but particularly at midand high latitudes where mean precipitation also increases.
However, in Figure 2.9 (lower part), there are regions of
increased runs of dry days between precipitation events in the
sub-tropics and lower mid-latitudes, but decreased runs of dry
days at higher mid-latitudes and high latitudes where mean
precipitation increases. [WGI 10.3.6.1]
Since there are areas of both increases and decreases in
consecutive dry days between precipitation events in the
Section 2
Observed and projected changes in climate as they relate to water
Figure 2.8: Fifteen-model mean changes in (a) precipitation (%), (b) soil moisture content (%), (c) runoff (%), and (d)
evaporation (%). To indicate consistency of sign of change, regions are stippled where at least 80% of models agree on
the sign of the mean change. Changes are annual means for the scenario SRES A1B for the period 2080–2099 relative to
1980–1999. Soil moisture and runoff changes are shown at land points with valid data from at least ten models. [Based on
WGI Figure 10.12]
multi-model average (Figure 2.9), the global mean trends
are smaller and less consistent across models. A perturbed
physics ensemble with one model shows only limited areas of
consistently increased frequency of wet days in July. In this
ensemble there is a larger range of changes in precipitation
extremes relative to the control ensemble mean (comparedwith
the more consistent response of temperature extremes). This
indicates a less consistent response for precipitation extremes
in general, compared with temperature extremes. [WGI 10.3.6,
FAQ10.1]
Based on a range of models, it is likely that future tropical
cyclones will become more intense, with larger peak wind
speeds and more heavy precipitation associated with ongoing
increases in tropical sea surface temperatures. There is less
confidence in projections of a global decrease in numbers of
tropical cyclones. [WGI SPM]
2.3.2
Snow and land ice
As the climate warms, snow cover is projected to contract
and decrease, and glaciers and ice caps to lose mass, as a
consequence of the increase in summer melting being greater
than the increase in winter snowfall. Widespread increases in
thaw depth over much of the permafrost regions are projected
to occur in response to warming. [WGI SPM, 10.3.3]
2.3.2.1
Changes in snow cover, frozen ground, lake and
iiiiiiiiiiiiiiiiriver ice
Snow cover is an integrated response to both temperature and
precipitation, and it exhibits a strong negative correlation with
air temperature in most areas with seasonal snow cover. Because
of this temperature association, simulations project widespread
reductions in snow cover throughout the 21st century, despite
some projected increases at higher altitudes. For example,
27
Observed and projected changes in climate as they relate to water
Section 2
climate models used in the Arctic Climate Impact Assessment
(ACIA) project a 9–17% reduction in the annual mean Northern
Hemisphere snow coverage under the B2 scenario by the end
of the century. In general, the snow accumulation season is
projected to begin later, the melting season to begin earlier,
and the fractional snow coverage to decrease during the snow
season. [WGI 10.3.3.2, Chapter 11]
Results from models forced with a range of IPCC climate
scenarios indicate that by the mid-21st century the permafrost
area in the Northern Hemisphere is likely to decrease by 20–
35%. Projected changes in the depth of seasonal thawing are
uniform neither in space nor in time. In the next three decades,
active layer depths are likely to be within 10–15% of their
present values over most of the permafrost area; by the middle
of the century, the depth of seasonal thawing may increase on
average by 15–25%, and by 50% or more in the northernmost
locations; by 2080, it is likely to increase by 30–50% or more
over all permafrost areas. [WGII 15.3.4]
Warming is forecast to cause reductions in river and lake ice.
This effect, however, is expected to be offset on some large
northward-flowing rivers because of reduced regional contrasts
in south-to-north temperatures and in related hydrological and
physical gradients. [WGII 15.4.1.2]
2.3.2.2
Glaciers and ice caps
As the climate warms throughout the 21st century, glaciers and
ice caps are projected to lose mass owing to a dominance of
summer melting over winter precipitation increases. Based on
simulations of 11 glaciers in various regions, a volume loss
of 60% of these glaciers is projected by 2050 (Schneeberger
et al., 2003). A comparative study including seven GCM
simulations at 2 × atmospheric CO2 conditions inferred that
many glaciers may disappear completely due to an increase
in the equilibrium-line altitude (Bradley et al., 2004). The
disappearance of these ice bodies is much faster than a potential
re-glaciation several centuries hence, and may in some areas
be irreversible. [WGI 10.7.4.2, Box 10.1] Global 21st-century
projections show glacier and ice cap shrinkage of 0.07–0.17 m
sea-level equivalent (SLE) out of today’s estimated glacier and
ice cap mass of 0.15–0.37 m SLE. [WGI Chapter 4, Table 4.1,
10, Table 10.7]
2.3.3
Sea level
Because our present understanding of some important effects
driving sea-level rise is too limited, AR4 does not assess the
likelihood, nor provide a best estimate or an upper bound for
sea-level rise. The projections do not include either uncertainties
in climate–carbon cycle feedbacks or the full effects of changes
in ice sheet flow; therefore the upper values of the ranges are
not to be considered upper bounds for sea-level rise. Modelbased projections of global mean sea-level rise between the
late 20th century (1980–1999) and the end of this century
(2090–2099) are of the order of 0.18 to 0.59 m, based on the
spread of AOGCM results and different SRES scenarios, but
excluding the uncertainties noted above. In all the SRES marker
28
Figure 2.9: Changes in extremes based on multi-model
simulations from nine global coupled climate models in
2080–2099 relative to 1980–1999 for the A1B scenario.
Changes in spatial patterns of precipitation intensity (defined
as the annual total precipitation divided by the number of
wet days) (top); and changes in spatial patterns of dry days
(defined as the annual maximum number of consecutive dry
days) (bottom). Stippling denotes areas where at least five
of the nine models concur in determining that the change
is statistically significant. Extreme indices are calculated
only over land. The changes are given in units of standard
deviations. [WGI Figure 10.18]
scenarios except B1, the average rate of sea-level rise during
the 21st century is very likely to exceed the 1961–2003 average
rate (1.8 ± 0.5 mm/yr). Thermal expansion is the largest
component, contributing 70–75% of the central estimate in
these projections for all scenarios. Glaciers, ice caps and the
Greenland ice sheet are also projected to contribute positively
to sea level. GCMs indicate that, overall, the Antarctic ice
sheet will receive increased snowfall without experiencing
substantial surface melting, thus gaining mass and contributing
negatively to sea level. Sea-level rise during the 21st century
is projected to have substantial geographical variability. [SYR
3.2.1; WGI SPM, 10.6.5, TS 5.2] Partial loss of the Greenland
and/or Antarctic ice sheets could imply several metres of sealevel rise, major changes in coastlines and inundation of low-
Observed and projected changes in climate as they relate to water
Section 2
lying areas, with the greatest effects in river deltas and lowlying islands. Current modelling suggests that such changes are
possible for Greenland over millennial time-scales, but because
dynamic ice flow processes in both ice sheets are currently
poorly understood, more rapid sea-level rise on century timescales cannot be excluded. [WGI SPM; WGII 19.3]
2.3.4
Evapotranspiration
Evaporative demand, or ‘potential evaporation’, is projected to
increase almost everywhere. This is because the water-holding
capacity of the atmosphere increases with higher temperatures,
but relative humidity is not projected to change markedly.
Water vapour deficit in the atmosphere increases as a result,
as does the evaporation rate (Trenberth et al., 2003). [WGI
Figures 10.9, 10.12; WGII 3.2, 3.3.1] Actual evaporation over
open water is projected to increase, e.g., over much of the
ocean [WGI Figure 10.12] and lakes, with the spatial variations
tending to relate to spatial variations in surface warming. [WGI
10.3.2.3, Figure 10.8] Changes in evapotranspiration over land
are controlled by changes in precipitation and radiative forcing,
and the changes would, in turn, impact on the water balance of
runoff, soil moisture, water in reservoirs, the groundwater table
and the salinisation of shallow aquifers. [WGII 3.4.2]
Carbon dioxide enrichment of the atmosphere has two potential
competing implications for evapotranspiration from vegetation.
On the one hand, higher CO2 concentrations can reduce
transpiration because the stomata of leaves, through which
transpiration from plants takes place, need to open less in order to
take up the same amount of CO2 for photosynthesis (see Gedney
et al., 2006, although other evidence for such a relationship is
difficult to find). Conversely, higher CO2 concentrations can
increase plant growth, resulting in increased leaf area, and
thus increased transpiration. The relative magnitudes of these
two effects vary between plant types and in response to other
influences, such as the availability of nutrients and the effects of
changes in temperature and water availability. Accounting for
the effects of CO2 enrichment on evapotranspiration requires the
incorporation of a dynamic vegetation model. A small number of
models now do this (Rosenberg et al., 2003; Gerten et al., 2004;
Gordon and Famiglietti, 2004; Betts et al., 2007), but usually at
the global, rather than catchment, scale. Although studies with
equilibrium vegetation models suggested that increased leaf
area may offset stomatal closure (Betts et al., 1997; Kergoat
et al., 2002), studies with dynamic global vegetation models
indicate that the effects of stomatal closure exceed those of
increasing leaf area. Taking into account CO2-induced changes
in vegetation, global mean runoff under a 2×CO2 climate has
been simulated to increase by approximately 5% as a result
of reduced evapotranspiration due to CO2 enrichment alone
(Leipprand and Gerten, 2006; Betts et al., 2007). [WGII 3.4.1]
2.3.5
Soil moisture
Changes in soil moisture depend on changes in the volume and
timing not only of precipitation, but also of evaporation (which
may be affected by changes in vegetation). The geographical
distribution of changes in soil moisture is therefore slightly
different from the distribution of changes in precipitation; higher
evaporation can more than offset increases in precipitation.
Models simulate the moisture in the upper few metres of the
land surface in varying ways, and evaluation of the soil moisture
content is still difficult. Projections of annual mean soil moisture
content (Figure 2.8b) commonly show decreases in the subtropics and the Mediterranean region, but there are increases in
East Africa, central Asia and some other regions with increased
precipitation. Decreases also occur at high latitudes, where
snow cover diminishes (Section 2.3.2). While the magnitude
of changes is often uncertain, there is consistency in the sign
of change in many of these regions. Similar patterns of change
occur in seasonal results. [WGI 10.3.2.3]
2.3.6
Runoff and river discharge
Changes in river flows, as well as lake and wetland levels, due
to climate change depend primarily on changes in the volume
and timing of precipitation and, crucially, whether precipitation
falls as snow or rain. Changes in evaporation also affect river
flows. Several hundred studies of the potential effects of climate
change on river flows have been published in scientific journals,
and many more studies have been presented in internal reports.
Studies are heavily focused towards Europe, North America
and Australasia, with a small number of studies from Asia.
Virtually all studies use a catchment hydrological model driven
by scenarios based on climate model simulations, and almost all
are at the catchment scale. The few global-scale studies that have
been conducted using both runoff simulated directly by climate
models [WGI 10.3.2.3] and hydrological models run off-line
[WGII 3.4] show that runoff increases in high latitudes and the
wet tropics, and decreases in mid-latitudes and some parts of
the dry tropics. Figure 2.8c shows the ensemble mean runoff
change under the A1B scenario. Runoff is notably reduced in
southern Europe and increased in south-east Asia and in high
latitudes, where there is consistency among models in the sign
of change (although less in the magnitude of change). The larger
changes reach 20% or more of the simulated 1980–1999 values,
which range from 1 to 5 mm/day in wetter regions to below
0.2 mm/day in deserts. Flows in high-latitude rivers increase,
while those from major rivers in the Middle East, Europe
and Central America tend to decrease. [WGI 10.3.2.3] The
magnitude of change, however, varies between climate models
and, in some regions such as southern Asia, runoff could either
increase or decrease. As indicated in Section 2.2.1, the effects
of CO2 enrichment may lead to reduced evaporation, and hence
either greater increases or smaller decreases in the volume of
runoff. [WGI 7.2]
Figure 2.10 shows the change in annual runoff for 2090–2099
compared with 1980–1999. Values represent the median of
12 climate models using the SRES A1B scenario. Hatching
and whitening are used to mark areas where models agree or
disagree, respectively, on the sign of change: note the large
areas where the direction of change is uncertain. This global
map of annual runoff illustrates large-scale changes and is not
intended to be interpreted at small temporal (e.g., seasonal) and
29
Observed and projected changes in climate as they relate to water
spatial scales. In areas where rainfall and runoff are very low
(e.g., desert areas), small changes in runoff can lead to large
percentage changes. In some regions, the sign of projected
changes in runoff differs from recently observed trends (Section
2.1.6). In some areas with projected increases in runoff, different
seasonal effects are expected, such as increased wet-season
runoff and decreased dry-season runoff. [WGII 3.4.1]
A very robust finding is that warming would lead to changes in
the seasonality of river flows where much winter precipitation
currently falls as snow, with spring flows decreasing because of
the reduced or earlier snowmelt, and winter flows increasing.
This has been found in the European Alps, Scandinavia and
around the Baltic, Russia, the Himalayas, and western, central
and eastern North America. The effect is greatest at lower
elevations, where snowfall is more marginal, and in many cases
peak flows by the middle of the 21st century would occur at least
a month earlier. In regions with little or no snowfall, changes in
runoff are much more dependent on changes in rainfall than on
Section 2
changes in temperature. Most studies in such regions project an
increase in the seasonality of flows, often with higher flows in
the peak flow season and either lower flows during the low-flow
season or extended dry periods. [WGII 3.4.1]
Many rivers draining glaciated regions, particularly in the
Asian high mountain ranges and the South American Andes, are
sustained by glacier melt during warm and dry periods. Retreat
of these glaciers due to global warming would lead to increased
river flows in the short term, but the contribution of glacier melt
would gradually fall over the next few decades. [WGII 3.4.1]
Changes in lake levels reflect changes in the seasonal distribution
of river inflows, precipitation and evaporation, in some cases
integrated over many years. Lakes may therefore respond in
a very non-linear way to a linear change in inputs. Studies of
the Great Lakes of North America and the Caspian Sea suggest
changes in water levels of the order of several tens of centimetres,
and sometimes metres, by the end of the century. [WGII 3.4.1]
Figure 2.10: Large-scale relative changes in annual runoff for the period 2090–2099, relative to 1980–1999. White areas are
where less than 66% of the ensemble of 12 models agree on the sign of change, and hatched areas are where more than 90%
of models agree on the sign of change (Milly et al., 2005). [Based on SYR Figure 3.5 and WGII Figure 3.4]
30
Observed and projected changes in climate as they relate to water
Section 2
2.3.7
Patterns of large-scale variability
Based on the global climate models assessed in AR4, sea-level
pressure is projected to increase over the sub-tropics and midlatitudes, and to decrease over high latitudes. These changes
are associated with an expansion of the Hadley Circulation and
positive trends in the Northern Annular Mode/North Atlantic
Oscillation (NAM/NAO) and the Southern Annular Mode
(SAM). As a result of these changes, storm tracks are projected
to move polewards, with consequent changes in wind,
precipitation and temperature patterns outside the tropics,
continuing the broad pattern of observed trends over the last
half-century. [WGI TS, 10.3.5.6, 10.3.6.4]
It is likely that future tropical cyclones will become more intense,
with larger peak wind speeds and heavier precipitation, associated
with ongoing increases of tropical SSTs. [WGI SPM, 10.3.6.3]
SSTs in the central and eastern equatorial Pacific are projected
to warm more than those in the western equatorial Pacific,
with a corresponding mean eastward shift in precipitation.
All models show continued El Niño–Southern Oscillation
(ENSO) interannual variability in the future, but large intermodel differences in projected changes in El Niño amplitude,
and the inherent multi-decadal time-scale variability of El
Niño in the models, preclude a definitive projection of trends
in ENSO variability. [WGI TS, 10.3.5.3, 10.3.5.4]
Interannual variability in monthly mean surface air
temperature is projected to decrease during the cold season
in the extra-tropical Northern Hemisphere and to increase at
low latitudes and warm-season northern mid-latitudes. The
former is probably due to the decrease in sea ice and snow
with increasing temperature. The summer decrease in soil
moisture over the mid-latitude land surfaces contributes to
the latter. Monthly mean precipitation variability is projected
to increase in most areas, both in absolute value (standard
deviation) and in relative value (coefficient of variation).
However, the significance level of these projected variability
changes is low. [WGI 10.3.5.1]
31
3
Linking climate change and water
resources: impacts and responses
Linking climate change and water resources: impacts and responses
Section 3
3.1 Observed climate change impacts
3.1.1
Observed effects due to changes in the
cryosphere
Effects of changes in the cryosphere have been documented in
relation to virtually all cryospheric components, with robust
evidence that they are, in general, a response to the reduction of
snow and ice masses due to enhanced warming.
3.1.1.1
Mountain glaciers and ice caps, ice sheets and ice shelves
Effects of changes in mountain glaciers and ice caps have been
documented in runoff (Kaser et al., 2003; Box et al., 2006),
changing hazard conditions (Haeberli and Burn, 2002) and
ocean freshening (Bindoff et al., 2007). There is also emerging
evidence of present crustal uplift in response to recent glacier
melting in Alaska (Larsen et al., 2005). The enhanced melting,
as well as the increased length of the melt season of glaciers,
leads at first to increased river runoff and discharge peaks, while
in the longer time-frame (decadal to century scale), glacier
runoff is expected to decrease (Jansson et al., 2003). Evidence
for increased runoff in recent decades due to enhanced glacier
melt has already been detected in the tropical Andes and in the
Alps. [WGI 4.6.2; WGII 1.3.1.1]
The formation of lakes is occurring as glaciers retreat from
prominent Little Ice Age (LIA) moraines in several steep
mountain ranges, including the Himalayas (see Box 5.4), the
Andes and the Alps. Thawing of buried ice also threatens to
destabilise the Little Ice Age moraines. These lakes thus have
a high potential for glacial lake outburst floods (GLOFs).
Governmental institutions in the respective countries have
undertaken extensive safety work, and several of the lakes are
now either solidly dammed or drained; but continued vigilance
is needed, since many tens of potentially dangerous glacial
lakes still exist in the Himalayas (Yamada, 1998) and the Andes
(Ames, 1998), together with several more in other mountain
ranges of the world. [WGII 1.3.1.1]
Glacier retreat causes striking changes in the landscape, which
has affected living conditions and local tourism in many mountain
regions around the world (Watson and Haeberli, 2004; Mölg et
al., 2005). Figure 5.10 shows the effects of the retreat of the
Chacaltaya Glacier on the local landscape and skiing industry.
Warming produces an enhanced spring–summer melting of
glaciers, particularly in areas of ablation, with a corresponding
loss of seasonal snow cover that results in increased exposure
of surface crevasses, which can in turn affect, for example,
snow runway operations, as has been reported in the Antarctic
Peninsula (Rivera et al., 2005). [WGII 1.3.1.1]
3.1.1.2
Snow cover and frozen ground
Due to less extended snow cover both in space and time, spring
peak river flows have been occurring 1–2 weeks earlier during
the last 65 years in North America and northern Eurasia. There
is also evidence for an increase in winter base flow in northern
Eurasia and North America, as well as a measured trend
towards less snow at low altitudes, which is affecting skiing
areas. [WGII 1.3.1.1]
Reductions in the extent of seasonally frozen ground and
permafrost, and an increase in active-layer thickness, have
resulted in:
• the disappearance of lakes due to draining within the
permafrost, as detected in Alaska (Yoshikawa and Hinzman,
2003) and Siberia (see Figure 5.12) (Smith et al., 2005);
• a decrease in potential travel days of vehicles over frozen
roads in Alaska;
• increased coastal erosion in the Arctic (e.g., Beaulieu and
Allard, 2003).
[WGII 1.3.1.1, Chapter 15]
3.1.2
Hydrology and water resources
3.1.2.1
Changes in surface and groundwater systems
Since the TAR there have been many studies related to trends
in river flows during the 20th century at scales ranging from
catchment to global. Some of these studies have detected
significant trends in some indicators of river flow, and some
have demonstrated statistically significant links with trends
in temperature or precipitation; but no globally homogeneous
trend has been reported. Many studies, however, have found no
trends, or have been unable to separate the effects of variations
in temperature and precipitation from the effects of human
interventions in the catchment, such as land-use change and
reservoir construction. Variation in river flows from year to year
is also very strongly influenced in some regions by large-scale
atmospheric circulation patterns associated with ENSO, NAO
and other variability systems that operate at within-decadal and
multi-decadal time-scales. [WGII 1.3.2.1]
At the global scale, there is evidence of a broadly coherent
pattern of change in annual runoff, with some regions
experiencing an increase (Tao et al., 2003a, b, for China;
Hyvarinen, 2003, for Finland; Walter et al., 2004, for the
coterminous USA), particularly at higher latitudes, and others a
decrease, for example in parts of West Africa, southern Europe
and southern Latin America (Milly et al., 2005). Labat et al.
(2004) claimed a 4% increase in global total runoff per 1°C
rise in temperature during the 20th century, with regional
variation around this trend, but this has been challenged due
to the effects of non-climatic drivers on runoff and bias due to
the small number of data points (Legates et al., 2005). Gedney
et al. (2006) gave the first tentative evidence that CO2 forcing
leads to increases in runoff due to the effects of elevated CO2
concentrations on plant physiology, although other evidence for
such a relationship is difficult to find. The methodology used
to search for trends can also influence results, since omitting
the effects of cross-correlation between river catchments can
lead to an overestimation of the number of catchments showing
significant trends (Douglas et al., 2000). [WGII 1.3.2.1]
35
Linking climate change and water resources: impacts and responses
Groundwater flow in shallow aquifers is part of the hydrological
cycle and is affected by climate variability and change through
recharge processes (Chen et al., 2002), as well as by human
interventions in many locations (Petheram et al., 2001). [WGII
1.3.2.1] Groundwater levels of many aquifers around the world
show a decreasing trend over the last few decades [WGII 3.2,
10.4.2], but this is generally due to groundwater pumping
surpassing groundwater recharge rates, and not to a climaterelated decrease in groundwater recharge. There may be regions,
such as south-western Australia, where increased groundwater
withdrawals have been caused not only by increased water
demand but also because of a climate-related decrease in
recharge from surface water supplies (Government of Western
Australia, 2003). In the upper carbonate aquifer near Winnipeg,
Canada, shallow well hydrographs show no obvious trends,
but exhibit variations of 3–4 years correlated with changes in
annual temperature and precipitation (Ferguson and George,
2003). Owing to a lack of data and the very slow reaction of
groundwater systems to changing recharge conditions, climaterelated changes in groundwater recharges have not been
observed. [WGII 1.3.2, 3.2]
At present, no globally consistent trend in lake levels has been
found. While some lake levels have risen in Mongolia and China
(Xinjiang) in response to increased snow- and ice melt, other
lake levels in China (Qinghai), Australia, Africa (Zimbabwe,
Zambia and Malawi), North America (North Dakota) and
Europe (central Italy) have declined due to the combined
effects of drought, warming and human activities. Within
permafrost areas in the Arctic, recent warming has resulted in
the temporary formation of lakes due to the onset of melting,
which then drain rapidly due to permafrost degradation (e.g.,
Smith et al., 2005). A similar effect has been reported for a lake
formed over an Arctic ice shelf (i.e., an epishelf lake12), which
disappeared when the ice shelf collapsed (Mueller et al., 2003).
Permafrost and epishelf lakes are treated in detail by Le Treut
et al. (2007). [WGII 1.3.2.1]
3.1.2.2
Water quality
A climate-related warming of lakes and rivers has been observed
over recent decades. [WGII 1.3.2] As a result, freshwater
ecosystems have shown changes in species composition,
organism abundance, productivity and phenological shifts
(including earlier fish migration). [WGII 1.3.4] Also due to
warming, many lakes have exhibited prolonged stratification
with decreases in surface layer nutrient concentration [WGII
1.3.2], and prolonged depletion of oxygen in deeper layers.
[WGII Box 4.1] Due to strong anthropogenic impacts not
related to climate change, there is no evidence for consistent
climate-related trends in other water quality parameters (e.g.,
salinity, pathogens or nutrients) in lakes, rivers and groundwater.
[WGII 3.2]
Thermal structure of lakes
Higher water temperatures have been reported in lakes in
response to warmer conditions (Table 3.1). Shorter periods
12
A body of water, mostly fresh, trapped behind an ice shelf.
36
Section 3
of ice cover and decreases in river- and lake-ice thickness are
treated in Section 2.1.2 and Le Treut et al. (2007). Phytoplankton
dynamics and primary productivity have also been altered in
conjunction with changes in lake physics. [WGII 1.3.4.4, Figure
1.2, Table 1.6] Since the 1960s, surface water temperatures
have warmed by between 0.2 and 2.0°C in lakes and rivers
in Europe, North America and Asia. Along with warming
surface waters, deep-water temperatures (which reflect longterm trends) of the large East African lakes (Edward, Albert,
Kivu, Victoria, Tanganyika and Malawi) have warmed by
between 0.2 and 0.7°C since the early 1900s. Increased water
temperature and longer ice-free seasons influence the thermal
stratification and internal hydrodynamics of lakes. In warmer
years, surface water temperatures are higher, evaporative water
loss increases, summer stratification occurs earlier in the season,
and thermoclines become shallower. In several lakes in Europe
and North America, the stratified period has advanced by up to
20 days and lengthened by 2–3 weeks, with increased thermal
stability. [WGII 1.3.2.3]
Chemistry
Increased stratification reduces water movement across the
thermocline, inhibiting the upwelling and mixing that provide
essential nutrients to the food web. There have been decreases
in nutrients in the surface water and corresponding increases
in deep-water concentrations of European and East African
lakes because of reduced upwelling due to greater thermal
stability. Many lakes and rivers have increased concentrations
of sulphates, base cations and silica, and greater alkalinity and
conductivity related to increased weathering of silicates, calcium
and magnesium sulphates, or carbonates, in their catchment.
In contrast, when warmer temperatures enhanced vegetative
growth and soil development in some high-alpine ecosystems,
alkalinity decreased because of increased organic acid inputs
(Karst-Riddoch et al., 2005). Glacial melting increased the
input of organochlorines (which had been atmospherically
transported to and stored in the glacier) to a sub-alpine lake in
Canada (Blais et al., 2001). [WGII 1.3.2.3]
Increased temperature also affects in-lake chemical processes
(Table 3.1; see also WGII Table SM1.3 for additional observed
changes in chemical water properties). There have been decreases
in dissolved inorganic nitrogen from greater phytoplankton
productivity (Sommaruga-Wograth et al., 1997; Rogora et al.,
2003) and greater in-lake alkalinity generation and increases in
pH in soft-water lakes (Psenner and Schmidt, 1992). Decreased
solubility from higher temperatures significantly contributed to
11–13% of the decrease in aluminium concentration (Vesely et
al., 2003), whereas lakes that had warmer water temperatures
had increased mercury methylation and higher mercury levels
in fish (Bodaly et al., 1993). A decrease in silicon content related
to regional warming has been documented in Lake Baikal,
Russia. River water-quality data from 27 rivers in Japan also
suggest a deterioration in both chemical and biological features
due to increases in air temperature. [WGII 1.3.2.3]
Linking climate change and water resources: impacts and responses
Section 3
Erosion and sedimentation
Water erosion has increased in many areas of the world, largely
as a consequence of anthropogenic land-use change. Due to lack
of data, there is no evidence for or against past climate-related
changes in erosion and sediment transport. [WGII 3.2]
3.1.2.3
Floods
A variety of climatic and non-climatic processes influence flood
processes, resulting in river floods, flash floods, urban floods,
sewer floods, glacial lake outburst floods (GLOFs, see Box 5.4)
and coastal floods. These flood-producing processes include
intense and/or long-lasting precipitation, snowmelt, dam break,
reduced conveyance due to ice jams or landslides, or by storm.
Floods depend on precipitation intensity, volume, timing,
phase (rain or snow), antecedent conditions of rivers and their
drainage basins (e.g., presence of snow and ice, soil character
and status (frozen or not, saturated or unsaturated), wetness,
rate and timing of snow/ice melt, urbanisation, existence of
dykes, dams and reservoirs). Human encroachment into flood
plains and lack of flood response plans increase the damage
potential. [WGII 3.4.3] The observed increase in precipitation
intensity and other observed climate changes, e.g., an increase
in westerly weather patterns during winter over Europe, leading
to very rainy low-pressure systems that often trigger floods
(Kron and Berz, 2007), indicate that climate change might
already have had an impact on the intensity and frequency of
floods. [WGII 3.2] The Working Group I AR4 Summary for
Policymakers concluded that it is likely that the frequency of
heavy precipitation events has increased over most areas during
the late 20th century, and that it is more likely than not that
there has been a human contribution to this trend. [WGI Table
SPM-2]
Globally, the number of great inland flood catastrophes during
the last 10 years (1996–2005) is twice as large, per decade, as
between 1950 and 1980, while related economic losses have
increased by a factor of five (Kron and Berz, 2007). Dominant
drivers of the upward trend of flood damage are socio-economic
factors such as economic growth, increases in population and
in the wealth concentrated in vulnerable areas, and land-use
change. Floods have been the most reported natural disaster
events in many regions, affecting 140 million people per year
on average (WDR, 2003, 2004). In Bangladesh, during the 1998
flood, about 70% of the country’s area was inundated (compared
to an average value of 20–25%) (Mirza, 2003; Clarke and King,
2004). [WGII 3.2]
Since flood damages have grown more rapidly than population
or economic growth, other factors must be considered, including
climate change (Mills, 2005). The weight of observational
evidence indicates an ongoing acceleration of the water cycle
(Huntington, 2006). [WGII 3.4.3] The frequency of heavy
precipitation events has increased, consistent with both
warming and observed increases in atmospheric water vapour.
[WGI SPM, 3.8, 3.9] However, no ubiquitous increase is visible
in documented trends in high river flows. Although Milly et al.
Table 3.1: Observed changes in runoff/streamflow, lake levels and floods/droughts. [WGII Table 1.3]
Environmental factor
Observed changes
Time period
Location
Runoff/streamflow
Annual increase of 5%, winter increase of 25–90%, increase in
winter base flow due to increased melt and thawing permafrost
1935–1999
Arctic Drainage Basin: Ob, Lena,
Yenisey, Mackenzie
1–2 week earlier peak streamflow due to earlier warmingdriven snowmelt
1936–2000
Western North America, New
England, Canada, northern
Eurasia
Floods
Increasing catastrophic floods of frequency (0.5–1%) due to
earlier break-up of river ice and heavy rain
Recent years
Russian Arctic rivers
Droughts
29% decrease in annual maximum daily streamflow due to
temperature rise and increased evaporation with no change in
precipitation
1847–1996
Southern Canada
Due to dry and unusually warm summers related to warming
of western tropical Pacific and Indian Oceans in recent years
1998–2004
Western USA
0.1–1.5°C increase in lakes
40 years
Europe, North America, Asia
(100 stations)
0.2–0.7°C increase (deep water) in lakes
100 years
East Africa (6 stations)
Decreased nutrients from increased stratification or longer
growing period in lakes and rivers
100 years
North America, Europe, Eastern
Europe, East Africa (8 stations)
Increased catchment weathering or internal processing in
lakes and rivers
10–20 years
North America, Europe
(88 stations)
Water temperature
Water chemistry
37
Linking climate change and water resources: impacts and responses
(2002) identified an apparent increase in the frequency of ‘large’
floods (return period >100 years) across much of the globe
from the analysis of data from large river basins, subsequent
studies have provided less widespread evidence. Kundzewicz
et al. (2005) found increases (in 27 locations) and decreases
(in 31 locations) and no trend in the remaining 137 of the 195
catchments examined worldwide. [WGII 1.3.2.2]
3.1.2.4
Droughts
The term drought may refer to a meteorological drought
(precipitation well below average), hydrological drought
(low river flows and low water levels in rivers, lakes and
groundwater), agricultural drought (low soil moisture), and
environmental drought (a combination of the above). The socioeconomic impacts of droughts may arise from the interaction
between natural conditions and human factors such as changes
in land use, land cover, and the demand for and use of water.
Excessive water withdrawals can exacerbate the impact of
drought. [WGII 3.4.3]
Droughts have become more common, especially in the tropics
and sub-tropics, since the 1970s. The Working Group I AR4
Summary for Policymakers concluded that it is likely that the
area affected by drought has increased since the 1970s, and it
is more likely than not that there is a human contribution to this
trend. [WGI Table SPM-2] Decreased land precipitation and
increased temperatures, which enhance evapotranspiration and
reduce soil moisture, are important factors that have contributed
to more regions experiencing droughts, as measured by the
Palmer Drought Severity Index (PDSI) (Dai et al., 2004b).
[WGII 3.3.4]
The regions where droughts have occurred seem to be determined
largely by changes in sea surface temperatures, especially in
the tropics, through associated changes in the atmospheric
circulation and precipitation. In the western USA, diminishing
snow pack and subsequent reductions in soil moisture also
appear to be factors. In Australia and Europe, direct links to
global warming have been inferred through the extreme nature
of high temperatures and heatwaves accompanying recent
droughts. [WGI 3.ES, 3.3.4]
Using the PDSI, Dai et al. (2004b) found a large drying trend
over Northern Hemisphere land since the mid-1950s, with
widespread drying over much of Eurasia, northern Africa,
Canada and Alaska (Figure 3.1). In the Southern Hemisphere,
land surfaces were wet in the 1970s and relatively dry in the
1960s and 1990s, and there was a drying trend from 1974 to
1998, although trends over the entire 1948 to 2002 period were
small. Decreases in land precipitation in recent decades are the
main cause for the drying trends, although large surface warming
during the last 2–3 decades is likely to have contributed to the
drying. Globally, very dry areas (defined as land areas with a
PDSI of less than −3.0) more than doubled (from ~12% to 30%)
since the 1970s, with a large jump in the early 1980s due to an
ENSO-related precipitation decrease over land, and subsequent
increases primarily due to surface warming (Dai et al., 2004b).
[WGI 3.3.4]
38
Section 3
Droughts affect rain-fed agricultural production as well as
water supply for domestic, industrial and agricultural purposes.
Some semi-arid and sub-humid regions, e.g., Australia. [WGII
11.2.1], western USA and southern Canada [WGII 14.2.1], and
the Sahel (Nicholson, 2005), have suffered from more intense
and multi-annual droughts. [WGII 3.2]
The 2003 heatwave in Europe, attributable to global warming
(Schär et al., 2004), was accompanied by annual precipitation
deficits up to 300 mm. This drought contributed to the estimated
30% reduction in gross primary production of terrestrial
ecosystems over Europe (Ciais et al., 2005). Many major rivers
(e.g., the Po, Rhine, Loire and Danube) were at record low
levels, resulting in disruption of inland navigation, irrigation
and power plant cooling (Beniston and Diaz, 2004; Zebisch et
al., 2005). The extreme glacier melt in the Alps prevented even
lower flows of the Danube and Rhine Rivers (Fink et al., 2004).
[WGII 12.6.1]
3.2 Future changes in water availability
iiiiiiiand demand due to climate change
3.2.1
Climate-related drivers of freshwater
iiiiiiiiiiiiiiiisystems in the future
The most dominant climate drivers for water availability are
precipitation, temperature and evaporative demand (determined
by net radiation at the ground, atmospheric humidity and wind
speed, and temperature). Temperature is particularly important
in snow-dominated basins and in coastal areas, the latter due to
the impact of temperature on sea level (steric sea-level rise due
to thermal expansion of water). [WGII 3.3.1]
Projected changes in these components of the water balance are
described in Section 2.3. In short, the total annual river runoff
over the whole land surface is projected to increase, even
though there are regions with significant increase and significant
decrease in runoff. However, increased runoff cannot be fully
utilised unless there is adequate infrastructure to capture and
store the extra water. Over the oceans, a net increase in the term
‘evaporation minus precipitation’ is projected.
3.2.1.1
Groundwater
Climate change affects groundwater recharge rates (i.e., the
renewable groundwater resources) and depths of groundwater
tables. However, knowledge of current recharge and levels in
both developed and developing countries is poor; and there has
been very little research on the future impact of climate change
on groundwater, or groundwater–surface water interactions. At
high latitudes, thawing of permafrost causes changes in both
the level and quality of groundwater, due to increased coupling
with surface waters. [WGII 15.4.1] As many groundwaters
both change into and are recharged from surface water,
impacts of surface water flow regimes are expected to affect
groundwater. Increased precipitation variability may decrease
groundwater recharge in humid areas because more frequent
Section 3
Linking climate change and water resources: impacts and responses
Figure 3.1: The most important spatial pattern (the first component of a principal components analysis; top) of the monthly
Palmer Drought Severity Index (PDSI) for 1900 to 2002. The PDSI is a prominent index of drought and measures the cumulative
deficit (relative to local mean conditions) in surface land moisture by incorporating previous precipitation and estimates of
moisture drawn into the atmosphere (based on atmospheric temperatures) into a hydrological accounting system.13 The lower
panel shows how the sign and strength of this pattern has changed since 1900. When the values shown in the lower plot are
positive (or negative), the red and orange areas in the upper map are drier (or wetter) and the blue and green areas are wetter
(or drier) than average. The smooth black curve shows decadal variations. The time-series approximately corresponds to a
trend, and this pattern and its variations account for 67% of the linear trend of PDSI from 1900 to 2002 over the global land
area. It therefore features widespread increasing African drought, especially in the Sahel, for instance. Note also the wetter
areas, especially in eastern North and South America and northern Eurasia (after Dai et al., 2004b). [WGI FAQ 3.2]
13
Note that the PDSI does not realistically model drought in regions where precipitation is held in the snowpack, for example, in polar regions.
39
Linking climate change and water resources: impacts and responses
heavy precipitation events may result in the infiltration capacity
of the soil being exceeded more often. In semi-arid and arid
areas, however, increased precipitation variability may increase
groundwater recharge, because only high-intensity rainfalls are
able to infiltrate fast enough before evaporating, and alluvial
aquifers are recharged mainly by inundations due to floods.
[WGII 3.4.2]
According to the results of a global hydrological model (see
Figure 3.2), groundwater recharge, when averaged globally,
increases less than total runoff (by 2% as compared with 9%
until the 2050s for the ECHAM4 climate change response to the
Section 3
SRES A2 scenario: Döll and Flörke, 2005). For all four climate
change scenarios investigated (the ECHAM4 and HadCM3
GCMs with the SRES A2 and B2 emissions scenarios14),
groundwater recharge was computed to decrease by the 2050s
by more than 70% in north-eastern Brazil, south-western Africa
and the southern rim of the Mediterranean Sea. However, as
this study did not take account of an expected increase in the
variability of daily precipitation, the decrease might be somewhat
overestimated. Where the depth of the water table increases and
groundwater recharge declines, wetlands dependent on aquifers
are jeopardised and the base flow runoff in rivers during dry
seasons is reduced. Regions in which groundwater recharge is
Figure 3.2: Simulated impact of climate change on long-term average annual diffuse groundwater recharge. Percentage
changes in 30-year average groundwater recharge between the present day (1961–1990) and the 2050s (2041–2070), as
computed by the global hydrological model WGHM, applying four different climate change scenarios (based on the ECHAM4
and HadCM3 climate models and the SRES A2 and B2 emissions scenarios) (Döll and Flörke, 2005). [WGII Figure 3.5]
14
See Appendix I for model descriptions.
40
Linking climate change and water resources: impacts and responses
Section 3
computed to increase by more than 30% by the 2050s include
the Sahel, the Near East, northern China, Siberia and the western
USA. In areas where water tables are already high, increased
recharge might cause problems in towns and agricultural areas
through soil salinisation and waterlogged soils. [WGII 3.4.2]
The few studies of climate change impacts on groundwater
for individual aquifers show very site-specific and climatemodel-specific results (e.g., Eckhardt and Ulbrich, 2003, for
a low mountain range catchment in Central Europe; Brouyere
et al., 2004, for a chalk aquifer in Belgium). For example, in
the Ogallala Aquifer region, projected natural groundwater
recharge decreases more than 20% in all simulations with
warming of 2.5°C or greater (Rosenberg et al., 1999). [WGII
14.4] As a result of climate change, in many aquifers of the
world the spring recharge shifts towards winter and summer
recharge declines. [WGII 3.4.2]
3.2.1.2 Floods
As discussed in Section 2.3.1, heavy precipitation events
are projected to become more frequent over most regions
throughout the 21st century. This would affect the risk of flash
flooding and urban flooding. [WGI 10.3.5, 10.3.6; WGII 3.4.3]
Some potential impacts are shown in Table 3.2.
In a multi-model analysis, Palmer and Räisänen (2002)
projected a considerable increase in the risk of a very wet
winter over much of central and northern Europe, this being
due to an increase in intense precipitation associated with
mid-latitude storms. The probability of total boreal winter
precipitation exceeding two standard deviations above normal
was projected to increase considerably (five- to seven-fold)
for a CO2-doubling over large areas of Europe, with likely
consequences for winter flood hazard. An increase in the risk
of a very wet monsoon season in Asia was also projected
(Palmer and Räisänen, 2002). According to Milly et al.
(2002), for 15 out of 16 large basins worldwide, the control
100-year peak volumes of monthly river flow are projected to
be exceeded more frequently for a CO2-quadrupling. In some
areas, what is given as a 100-year flood now (in the control
run), is projected to occur much more frequently, even every
2–5 years, albeit with a large uncertainty in these projections.
In many temperate regions, the contribution of snowmelt to
spring floods is likely to decline (Zhang et al., 2005). [WGII
3.4.3]
Based on climate models, the area flooded in Bangladesh
is projected to increase by at least 23–29% with a global
temperature rise of 2°C (Mirza, 2003). [WGII 3.4.3]
Table 3.2: Examples of possible impacts of climate change due to changes in extreme precipitation-related weather and climate
events, based on projections to the mid- to late 21st century. These do not take into account any changes or developments in
adaptive capacity. The likelihood estimates in column 2 relate to the phenomena listed in column 1. The direction of trend and
likelihood of phenomena are for IPCC SRES projections of climate change. [WGI Table SPM-2; WGII Table SPM-2]
Phenomenona and
direction
of trend
a
Likelihood of future
trends based on
projections for
21st century using
SRES scenarios
Examples of major projected impacts by sector
Agriculture, forestry
and ecosystems
[4.4, 5.4]
Damage to crops; soil
erosion; inability to
cultivate land due to
waterlogging of soils
Heavy
precipitation
events: frequency
increases over
most areas
Very likely
Area affected by
drought increases
Likely
Land degradation,
lower yields/crop
damage and failure;
increased livestock
deaths; increased
risk of wildfire
Intense tropical
cyclone activity
increases
Likely
Damage to crops;
windthrow (uprooting)
of trees; damage to
coral reefs
Water resources
[3.4]
Human health
[8.2]
Industry, settlements
and society [7.4]
Adverse effects on
quality of surface
and groundwater;
contamination of
water supply; water
scarcity may be
relieved
More widespread
water stress
Increased risk of
deaths, injuries
and infectious,
respiratory and
skin diseases
Disruption of
settlements, commerce,
transport and societies
due to flooding;
pressures on urban and
rural infrastructures;
loss of property
Water shortages for
settlements, industry
and societies; reduced
hydropower generation
potentials; potential for
population migration
Power outages
causing disruption of
public water supply
Increased risk of
deaths, injuries,
water- and foodborne diseases;
post-traumatic
stress disorders
Increased risk
of food and
water shortage;
increased risk
of malnutrition;
increased risk of
water- and foodborne diseases
Disruption by flood and
high winds; withdrawal
of risk coverage in
vulnerable areas
by private insurers;
potential for population
migrations; loss of
property
See Working Group I Fourth Assessment Table 3.7 for further details regarding definitions.
41
Linking climate change and water resources: impacts and responses
Warming-induced reduction of firn15 cover on glaciers causes
enhanced and immediate runoff of melt water and can lead to
flooding of glacial-fed rivers. [WGII 3.4.3]
There is a degree of uncertainty in estimates of future changes
in flood frequency across the UK. Depending on which climate
model is used, and on the importance of snowmelt contribution
and catchment characteristics and location, the impact of climate
change on the flood regime (magnitude and frequency) can be
positive or negative, highlighting the uncertainty still remaining
in climate change impacts (Reynard et al., 2004). [WGII 3.4.3]
3.2.1.3
Droughts
It is likely that the area affected by drought will increase. [WGI
SPM] There is a tendency for drying of mid-continental areas
during summer, indicating a greater risk of droughts in these
Section 3
regions. [WGI 10.ES] In a single-model study of global drought
frequency, the proportion of the land surface experiencing
extreme drought at any one time, the frequency of extreme
drought events, and the mean drought duration, were projected
to increase by 10- to 30-fold, two-fold, and six-fold, respectively,
by the 2090s, for the SRES A2 scenario (Burke et al., 2006).
[WGI 10.3.6; WGII 3.4.3] A decrease in summer precipitation in
southern and central Europe, accompanied by rising temperatures
(which enhance evaporative demand), would inevitably lead
to both reduced summer soil moisture (cf. Douville et al.,
2002; Christensen et al., 2007) and more frequent and intense
droughts. [WGII 3.4.3] As shown in Figure 3.3, by the 2070s, a
100-year drought16 of today’s magnitude is projected to return,
on average, more frequently than every 10 years in parts of
Spain and Portugal, western France, Poland’s Vistula Basin and
western Turkey (Lehner et al., 2005). [WGII 3.4.3]
Figure 3.3: Change in the future recurrence of 100-year droughts, based on comparisons between climate and water use in
1961–1990 (Lehner et al., 2005). [WGII Figure 3.6]
15
16
Firn: aged snow (still permeable) that is at an intermediate stage towards becoming glacial ice (impermeable).
Every year, the chance of exceedence of the 100-year flood is 1%, while the chance of exceedence of the 10-year flood is 10%.
42
Section 3
Linking climate change and water resources: impacts and responses
Some impacts of increased drought area are shown in Table
3.2. Snowmelt is projected to become earlier and less abundant
in the melt period, and this may increase the risk of droughts
in snowmelt-fed basins in the low-flow season – summer and
autumn. An increase in drought risk is projected for regions
which depend heavily on glacial melt water for their main
dry-season water supply (Barnett et al., 2005). In the Andes,
glacial melt water supports river flow and water supply for
tens of millions of people during the long dry season. Many
small glaciers, e.g., in Bolivia, Ecuador and Peru (cf. Ramírez
et al., 2001; Box 5.5), are expected to disappear within the
next few decades. Water supply in areas fed by glacial and
snow melt water from the Hindu Kush and Himalayas, on
which hundreds of millions of people in China, Pakistan and
India depend, will be adversely affected (Barnett et al., 2005).
[WGII 3.4.3]
3.2.1.4 Water quality
Higher water temperatures, increased precipitation intensity,
and longer periods of low flows are projected to exacerbate
many forms of water pollution, including sediments, nutrients,
dissolved organic carbon, pathogens, pesticides, salt and
thermal pollution. This will promote algal blooms (Hall et
al., 2002; Kumagai et al., 2003), and increase the bacterial
and fungal content (Environment Canada, 2001). This will, in
turn, impact ecosystems, human health, and the reliability and
operating costs of water systems. [WGII 3.ES]
Rising temperatures are likely to lower water quality in lakes
through increased thermal stability and altered mixing patterns,
resulting in reduced oxygen concentrations and an increased
release of phosphorus from the sediments. For example, already
high phosphorus concentrations during summer in a bay of
Lake Ontario could double with a 3–4°C increase in water
temperature (Nicholls, 1999). However, rising temperatures
can also improve water quality during winter/spring due to
earlier ice break-up and consequent higher oxygen levels and
reduced winter fish-kill. [WGII 4.4.8, 14.4.1]
More intense rainfall will lead to an increase in suspended
solids (turbidity) in lakes and reservoirs due to soil fluvial
erosion (Leemans and Kleidon, 2002), and pollutants will be
introduced (Mimikou et al., 2000; Neff et al., 2000; Bouraoui
et al., 2004). The projected increase in precipitation intensity
is expected to lead to a deterioration of water quality, as it
results in the enhanced transport of pathogens and other
dissolved pollutants (e.g., pesticides) to surface waters and
groundwater; and in increased erosion, which in turn leads to
the mobilisation of adsorbed pollutants such as phosphorus
and heavy metals. In addition, more frequent heavy rainfall
events will overload the capacity of sewer systems and water
and wastewater treatment plants more often. [WGII 3.4.4]
An increased occurrence of low flows will lead to decreased
contaminant dilution capacity, and thus higher pollutant
concentrations, including pathogens. [WGII 3.4.4, 14.4.1] In
areas with overall decreased runoff (e.g., in many semi-arid
areas), water quality deterioration will be even worse.
In semi-arid and arid areas, climate change is likely to
increase salinisation of shallow groundwater due to increased
evapotranspiration. [WGII 3.4.2] As streamflow is projected
to decrease in many semi-arid areas, the salinity of rivers and
estuaries will increase. [WGII 3.4.4] For example, salinity levels
in the headwaters of the Murray-Darling Basin in Australia
are expected to increase by 13–19% by 2050 (Pittock, 2003).
In general, decreased groundwater recharge, which reduces
mobilisation of underground salt, may balance the effect of
decreased dilution of salts in rivers and estuaries. [WGII 11.4]
In coastal areas, rising sea levels may have negative effects
on storm-water drainage and sewage disposal [WGII 3.4.4]
and increase the potential for the intrusion of saline water into
fresh groundwater in coastal aquifers, thus adversely affecting
groundwater resources. [WGII 3.4.2] For two small and flat
coral islands off the coast of India, the thickness of freshwater
lenses was computed to decrease from 25 m to 10 m and from
36 m to 28 m, respectively, for a sea-level rise of only 0.1 m
(Bobba et al., 2000). Any decrease in groundwater recharge
will exacerbate the effect of sea-level rise. In inland aquifers,
a decrease in groundwater recharge can lead to saltwater
intrusion from neighbouring saline aquifers (Chen et al., 2004).
[WGII 3.4.2]
3.2.1.5 Water erosion and sedimentation
All studies on soil erosion show that the expected increase in
rainfall intensity would lead to greater rates of erosion. [WGII
3.4.5] In addition, the shift of winter precipitation from less
erosive snow to more erosive rainfall due to increasing winter
temperatures enhances erosion, with this leading, for example,
to negative water quality impacts in agricultural areas.
[WGII 3.4.5, 14.4.1]
The melting of permafrost induces an erodible state in soil which
was previously non-erodible. [WGII 3.4.5] Further indirect
impacts of climate change on erosion are related to soil and
vegetation changes caused by climate change and associated
adaptation actions. [WGII 3.4.5] The very few studies on
the impact of climate change on sediment transport suggest
transport enhancement due to increased erosion, particularly in
areas with increased runoff. [WGII 3.4.5]
3.2.2
Non-climatic drivers of freshwater systems
iiiiiiiiiiiiiiiiin the future
Many non-climatic drivers affect freshwater resources at the
global scale (UN, 2003). Both the quantity and quality of water
resources are influenced by land-use change, construction and
management of reservoirs, pollutant emissions and water
and wastewater treatment. Water use is driven by changes
in population, food consumption, economy (including water
pricing), technology, lifestyle and societal views regarding
the value of freshwater ecosystems. The vulnerability of
freshwater systems to climate change also depends on national
and international water management. It can be expected that
43
Linking climate change and water resources: impacts and responses
the paradigm of ‘integrated water resources management’
(IWRM)17 will be followed increasingly around the world
(UN, 2002; World Bank, 2004a; World Water Council, 2006),
and that such a movement has the potential to position water
issues, both as a resource and an ecosystem, at the centre of the
policy-making arena. This is likely to decrease the vulnerability
of freshwater systems to climate change. Consideration of
environmental flow requirements may lead to the modification
of reservoir operations so that human use of these water
resources might be restricted. [WGII 3.3.2]
3.2.3
Impacts of climate change on freshwater
availability in the future
With respect to water supply, it is very likely that the costs of
climate change will outweigh the benefits globally. One reason is
that precipitation variability is very likely to increase, and more
frequent floods and droughts are anticipated, as discussed in
Sections 2.1.6 and 2.3.1. The risk of droughts in snowmelt-fed
basins in the low-flow season will increase, as discussed in Section
3.2.1. The impacts of floods and droughts could be tempered by
appropriate infrastructure investments and by changes in water
and land-use management, but the implementation of such
measures will entail costs (US Global Change Research Program,
2000). Water infrastructure, usage patterns and institutions have
developed in the context of current conditions. Any substantial
change in the frequency of floods and droughts, or in the quantity
and quality or seasonal timing of water availability, will require
adjustments that may be costly, not only in monetary terms but
also in terms of societal and ecological impacts, including the
need to manage potential conflicts between different interest
groups (Miller et al., 1997). [WGII 3.5]
Hydrological changes may have impacts that are positive in
some aspects and negative in others. For example, increased
annual runoff may produce benefits for a variety of both instream
and out-of-stream water users by increasing renewable water
resources, but may simultaneously generate harm by increasing
flood risk. In recent decades, a trend to wetter conditions in parts
of southern South America has increased the area inundated
by floods, but has also improved crop yields in the Pampas
region of Argentina, and has provided new commercial fishing
opportunities (Magrin et al., 2005). [WGII 13.2.4] Increased
runoff could also damage areas with a shallow water table. In such
areas, a water-table rise disturbs agricultural use and damages
buildings in urban areas. In Russia, for example, the current
annual damage caused by shallow water tables is estimated to be
US$5–6 billion (Kharkina, 2004) and is likely to increase in the
future. In addition, an increase in annual runoff may not lead to
a beneficial increase in readily available water resources, if that
additional runoff is concentrated during the high-flow season.
[WGII 3.5]
Section 3
Increased precipitation intensity may result in periods of
increased turbidity and nutrient and pathogen loadings to
surface water sources. The water utility serving New York City
has identified heavy precipitation events as one of its major
climate-change-related concerns because such events can raise
turbidity levels in some of the city’s main reservoirs up to 100
times the legal limit for source quality at the utility’s intake,
requiring substantial additional treatment and monitoring costs
(Miller and Yates, 2006). [WGII 3.5.1]
3.2.4
Impacts of climate change on freshwater
demand in the future
Higher temperatures and increased variability of precipitation
would, in general, lead to increased irrigation water demand,
even if the total precipitation during the growing season
remains the same. The impact of climate change on optimal
growing periods, and on yield-maximising irrigation water
use, has been modelled assuming no change in either irrigated
area and/or climate variability (Döll, 2002; Döll et al., 2003).
Applying the IPCC SRES A2 and B2 scenarios as interpreted
by two climate models, it was projected that the net irrigation
requirements of China and India, the countries with the largest
irrigated areas worldwide, would change by +2% to +15% in
the case of China, and by −6% to +5% in the case of India,
by 2020, depending on emissions scenarios and climate model
(Döll, 2002; Döll et al., 2003). Different climate models project
different worldwide changes in net irrigation requirements,
with estimated increases ranging from 1–3% by the 2020s and
2–7% by the 2070s. The largest global-scale increases in net
irrigation requirements result from a climate scenario based on
the B2 emissions scenario. [WGII 3.5.1]
In a study of maize irrigation in Illinois under profit-maximising
conditions, it was found that a 25% decrease in annual
precipitation had the same effect on irrigation profitability
as a 15% decrease combined with a doubling of the standard
deviation of daily precipitation (Eheart and Tornil, 1999). This
study also showed that profit-maximising irrigation water use
responds more strongly to changes in precipitation than does
yield-maximising water use, and that a doubling of atmospheric
CO2 has only a small effect. [WGII 3.5.1]
The increase in household water demand (for example through
an increase in garden watering) and industrial water demand, due
to climate change, is likely to be rather small, e.g., less than 5%
by the 2050s at selected locations (Mote et al., 1999; Downing
et al., 2003). An indirect, but small, secondary effect would be
increased electricity demand for the cooling of buildings, which
would tend to increase water withdrawals for the cooling of
thermal power plants. A statistical analysis of water use in New
The prevailing concept for water management which, however, has not been defined unambiguously. IWRM is based on four principles that
iiiwere formulated by the International Conference on Water and the Environment in Dublin, 1992: (1) freshwater is a finite and vulnerable
iiiresource, essential to sustain life, development and the environment; (2) water development and management should be based on a participatory
iiiapproach, involving users, planners and policymakers at all levels; (3) women play a central part in the provision, management and safeguarding
iiiof water; (4) water has an economic value in all its competing uses and should be recognised as an economic good.
17
44
Linking climate change and water resources: impacts and responses
Section 3
York City showed that daily per capita water use on days above
25°C increases by 11 litres/°C (roughly 2% of current daily per
capita use) (Protopapas et al., 2000). [WGII 3.5.1]
3.2.5
Impacts of climate change on water stress
in the future
Global estimates of the number of people living in areas with
water stress differ significantly between studies (Vörösmarty
et al., 2000; Alcamo et al., 2003a, b, 2007; Oki et al., 2003;
Arnell, 2004). Nevertheless, climate change is only one of
many factors that influence future water stress; demographic,
socio-economic and technological changes possibly play more
important roles at most time horizons and in most regions.
In the 2050s, differences in the population projections of the
four IPCC SRES scenarios would have a greater impact on
the number of people living in water-stressed river basins than
the differences in the climate scenarios (Arnell, 2004). The
number of people living in water-stressed river basins would
increase significantly (Table 3.3). The change in the number of
people expected to be under water stress after the 2050s greatly
depends on the SRES scenario adopted. A substantial increase
is projected under the A2 scenario, while the rate of increase
is lower under the A1 and B1 scenarios because of the global
increase in renewable freshwater resources and a slight decrease
in population (Oki and Kanae, 2006). It should be noted that,
using the per capita water availability indicator, climate change
would appear to reduce overall water stress at the global level.
This is because increases in runoff are concentrated heavily in
the most populous parts of the world, mainly in eastern and
south-eastern Asia. However, given that this increased runoff
occurs mainly during high-flow seasons (Arnell, 2004), it may
not alleviate dry-season problems if the extra water is not stored;
and would not ease water stress in other regions of the world.
Changes in seasonal patterns and an increasing probability
of extreme events may offset the effects of increased annual
available freshwater resources and demographic changes.
[WGII 3.5.1]
If water stress is assessed not only as a function of population and
climate change but also of changing water use, the importance
of non-climatic drivers (income, water-use efficiency, water
Table 3.3: Impact of population growth and climate change
on the number of people living in water-stressed river basins
(defined as per capita renewable water resources of less than
1,000 m3/yr) around 2050. [WGII Table 3.2]
Estimated population in water-stressed
river basins in the year 2050 (billions)
Arnell (2004)
Alcamo et al. (2007)
1995: Baseline
1.4
1.6
2050: A2 emissions
scenario
4.4–5.7
6.4–6.9
2050: B2 emissions
scenario
2.8–4.0
4.9–5.2
Estimates are based on emissions scenarios for several climate model runs. The
range is due to the various climate models and model runs that were used to
translate emissions into climate scenarios
productivity, and industrial production) increases (Alcamo et
al., 2007). Income growth sometimes has a larger impact than
population growth on increasing water use and water stress
(when expressed as the water withdrawal: water resources
ratio). Water stress is modelled to decrease by the 2050s over
20–29% of the global land area and to increase over 62–76%
of the global land area (considering two climate models and
the SRES scenarios A2 and B2). The greater availability of
water due to increased precipitation is the principal cause of
decreasing water stress, while growing water withdrawals
are the principal cause of increasing water stress. Growth of
domestic water use, as stimulated by income growth, was found
to be dominant (Alcamo et al., 2007). [WGII 3.5.1]
3.2.6
Impacts of climate change on costs and
other socio-economic aspects of freshwater
The amount of water available for withdrawal is a function of
runoff, groundwater recharge, aquifer conditions (e.g., degree of
confinement, depth, thickness and boundaries), water quality and
water supply infrastructure (e.g., reservoirs, pumping wells and
distribution networks). Safe access to drinking water depends
more on the level of water supply infrastructure than on the
quantity of runoff. However, the goal of improved safe access to
drinking water will be harder to achieve in regions where runoff
and/or groundwater recharge decreases as a result of climate
change. In addition, climate change leads to additional costs
for the water supply sector, e.g., due to changing water levels
affecting water supply infrastructure, which might hamper the
extension of water supply services to more people. This leads,
in turn, to higher socio-economic impacts and follow-up costs,
especially in areas where the prevalence of water stress has also
increased as a result of climate change. [WGII 3.5.1]
Climate change-induced changes in both the seasonal runoff
regime and interannual runoff variability can be as important
for water availability as changes in the long-term average
annual runoff (US Global Change Research Program, 2000).
People living in snowmelt-fed basins experiencing decreasing
snow storage in winter may be negatively affected by decreased
river flows in the summer and autumn (Barnett et al., 2005). The
Rhine, for example, might suffer from a reduction of summer
low flows of 5–12% by the 2050s, which will negatively affect
water supply, particularly for thermal power plants (Middelkoop
et al., 2001). Studies for the Elbe River Basin showed that actual
evapotranspiration is projected to increase by 2050 (Krysanova
and Wechsung, 2002), while river flow, groundwater recharge,
crop yield and diffuse source pollution are likely to decrease
(Krysanova et al., 2005). [WGII 3.5.1]
In western China, earlier spring snowmelt and declining
glaciers are likely to reduce water availability for irrigated
agriculture. Investment and operation costs for the additional
wells and reservoirs which are required to guarantee a reliable
water supply under climate change have been estimated for
China. This cost is low in basins where the current water stress
is low (e.g., Changjiang) and high where water stress is high
45
Linking climate change and water resources: impacts and responses
Section 3
(e.g., Huanghe River) (Kirshen et al., 2005a). Furthermore, the
impact of climate change on water supply cost will increase in
the future, not only because of stronger climate change, but also
due to increasing demands. [WGII 3.5.1]
the exposure of people to natural hazards due to the lack of social
infrastructure, since the explanatory power of the model including
population and wealth is 82%, while adding precipitation increases
this to 89%. [WGII 3.5.2]
For an aquifer in Texas, the net income of farmers is projected
to decrease by 16–30% by the 2030s and by 30–45% by the
2090s due to decreased irrigation water supply and increased
irrigation water demand. Net benefit in total due to water use
(dominated by municipal and industrial use) is projected to
decrease by less than 2% over the same period (Chen et al.,
2001). [WGII 3.5.1]
Another study examined the potential flood damage impacts of
changes in extreme precipitation events by using the Canadian
Climate Center model and the IS92a scenario for the metro Boston
area in the north-eastern USA (Kirshen et al., 2005b). This study
found that, without adaptation investments, both the number of
properties damaged by floods and the overall cost of flood damage
would double by 2100, relative to what might be expected if
there was no climate change. It also found that flood-related
transportation delays would become an increasingly significant
nuisance over the course of this century. The study concluded that
the likely economic magnitude of these damages is sufficiently
high to justify large expenditures on adaptation strategies such as
universal flood-proofing in floodplains. [WGII 3.5.2]
If freshwater supply has to be replaced by desalinated water
due to climate change, then the cost of climate change includes
the average cost of desalination, which is currently around
US$1.00/m3 for seawater and US$0.60/m3 for brackish water
(Zhou and Tol, 2005). The cost for freshwater chlorination is
approximately US$0.02/m3. In densely populated coastal areas
of Egypt, China, Bangladesh, India and south-east Asia (FAO,
2003), desalination costs may be prohibitive. In these areas,
particularly in Egypt, research in new desalination technology
is required to reduce the costs, especially with the use of nonconventional energy sources that are associated with lower
greenhouse-gas emissions. In addition, the desalination of
brackish water can improve the economics of such projects (see
Section 4.4.4). [WGII 3.5.1]
Future flood damages will depend greatly on settlement
patterns, land-use decisions, the quality of flood forecasting,
warning and response systems, and the value of structures and
other property located in vulnerable areas (Mileti, 1999; Pielke
and Downton, 2000; Changnon, 2005), as well as on climatic
changes per se, such as changes in the frequency of tropical
cyclones (Schiermeier, 2006). [WGII 3.5.2]
The impact of climate change on flood damages can be
projected, based on modelled changes in the recurrence interval
of current 20- or 100-year floods and in conjunction with
flood damages from current events as determined from stagedischarge relations and detailed property data. With such a
methodology, the average annual direct flood damage for three
Australian drainage basins was projected to increase four- to
ten-fold under doubled CO2 conditions (Schreider et al., 2000).
[WGII 3.5.2]
Choi and Fisher (2003) estimated the expected change in flood
damages for selected US regions under two climate change
scenarios in which mean annual precipitation increased by
13.5% and 21.5%, respectively, with the standard deviation of
annual precipitation either remaining unchanged or increasing
proportionally to the mean. Using a structural econometric
(regression) model based on a time-series of flood damage and
with population, a wealth indicator and annual precipitation as
predictors, the mean and standard deviation of flood damage
are projected to increase by more than 140% if the mean and
standard deviation of annual precipitation increase by 13.5%.
This estimate suggests that flood losses are related primarily to
46
These findings are also supported by a scenario study on the
damages from river and coastal flooding in England and Wales
in the 2080s, which combined four emissions scenarios with four
scenarios of socio-economic change in an SRES-like framework
(Hall et al., 2005). In all scenarios, flood damages are projected
to increase unless current flood management policies, practices
and infrastructure are changed. By the 2080s, annual damage is
projected to be £5 billion in a B1-type world, as compared with
£1 billion today, while with approximately the same climate
change, damage is only £1.5 billion in a B2-type world. Both the
B1 and B2 scenarios give approximately similar results if these
numbers are normalised with respect to gross domestic product. In
an A1-type world, the annual damage would amount to £15 billion
by the 2050s and £21 billion by the 2080s (Evans et al., 2004; Hall
et al., 2005). [WGII 3.5.2]
Increased flood periods in the future would disrupt navigation
more often, and low flow conditions that restrict the loading of
ships may increase. For example, restrictions on loading in the
Rhine River may increase from 19 days under current climate
conditions to 26–34 days in the 2050s (Middelkoop et al., 2001).
[WGII 3.5.1]
Climate-change is likely to alter river discharge, resulting in
important impacts on water availability for instream usage,
particularly hydropower generation. Hydropower impacts for
Europe have been estimated using a macro-scale hydrological
model. The results indicate that by the 2070s the electricity
production potential of hydropower plants existing at the end of
the 20th century will increase (assuming IS92a emissions) by
15–30% in Scandinavia and northern Russia, where currently
between 19% (Finland) and almost 100% (Norway) of electricity
is produced by hydropower (Lehner et al., 2005). Decreases of
20–50% and more are found for Portugal, Spain, Ukraine and
Bulgaria, where currently between 10% (Ukraine, Bulgaria)
and 39% of the electricity is produced by hydropower (Lehner
et al., 2005). For the whole of Europe (with a 20% hydropower
fraction), hydropower potential is projected to decrease by 7–12%
by the 2070s. [WGII 3.5.1]
Linking climate change and water resources: impacts and responses
Section 3
In North America, potential reductions in the outflow of the
Great Lakes could result in significant economic losses as a
result of reduced hydropower generation both at Niagara and
on the St. Lawrence River (Lofgren et al., 2002). For a CGCM1
model projection with 2°C global warming, Ontario’s Niagara
and St. Lawrence hydropower generation would decline by 25–
35%, resulting in annual losses of Canadian $240–350 million
at 2002 prices (Buttle et al., 2004). With the HadCM218 climate
model, however, a small gain in hydropower potential (+3%)
was found, worth approximately Canadian $25 million per
year. Another study that examined a range of climate model
scenarios found that a 2°C global warming could reduce
hydropower generating capacity on the St. Lawrence River by
1–17% (LOSLR, 2006). [WGII 3.5.1]
3.2.7
Freshwater areas and sectors highly
vulnerable to climate change
In many regions of the globe, climate change impacts on
freshwater resources may affect sustainable development and
put at risk, for example, the reduction of poverty and child
mortality. Even with optimal water management, it is very
likely that negative impacts on sustainable development cannot
be avoided. Figure 3.4 shows some key cases around the
world, where freshwater-related climate change impacts are a
threat to the sustainable development of the affected regions.
‘Sustainable’ water resources management is generally sought
to be achieved by integrated water resources management
(IWRM: see Footnote 17 for a definition). However, the precise
interpretation of this term varies considerably. All definitions
broadly include the concept of maintaining and enhancing the
environment, and particularly the water environment, taking into
account competing users, instream ecosystems and wetlands.
They also consider the wider environmental implications of
water management policies such as the implications of water
management policies on land management and, conversely,
the implications of land management policies on the water
environment. Water governance is an important component of
managing water to achieve sustainable water resources for a
range of political, socio-economic and administrative systems
(GWP, 2002; Eakin and Lemos, 2006). [WGII 3.7]
3.2.8
Uncertainties in the projected impacts of
climate change on freshwater systems
Uncertainties in climate change impacts on water resources are
mainly due to the uncertainty in precipitation inputs and less
due to the uncertainties in greenhouse gas emissions (Döll et al.,
Figure 3.4: Illustrative map of future climate change impacts related to freshwater which threaten the sustainable development
of the affected regions. 1: Bobba et al. (2000), 2: Barnett et al. (2004), 3: Döll and Flörke (2005), 4: Mirza et al. (2003), 5:
Lehner et al. (2005), 6: Kistemann et al. (2002), 7: Porter and Semenov (2005). Background map, see Figure 2.10: Ensemble
mean change in annual runoff (%) between present (1980–1999) and 2090–2099 for the SRES A1B emissions scenario (based
on Milly et al., 2005). Areas with blue (red) colours indicate the increase (decrease) of annual runoff. [Based on WGII Figure
3.8 and SYR Figure 3.5]
18
See Appendix I for model descriptions.
47
Linking climate change and water resources: impacts and responses
2003; Arnell, 2004), in climate sensitivities (Prudhomme et al.,
2003), or in hydrological models themselves (Kaspar, 2003). A
further source of uncertainty regarding the projected impacts
of climate change on freshwater systems is the nature, extent,
and relative success of those initiatives and measures already
planned as interventions. The impacts illustrated in Figure 3.4
would be realised differently depending on any adaptation
measures taken. The feedbacks from adaptation measures
to climate change are not fully considered in current future
predictions, such as the longer growing season of crops and
more regulations on river flow, with increased reservoir storage.
The comparison of different sources of uncertainty in flood
statistics in two UK catchments (Kay et al., 2006a) led to the
conclusion that the largest source of uncertainty was the GCM
structure, followed by the emissions scenarios and hydrological
modelling. Similar conclusions were made by Prudhomme and
Davies (2006) in regard to mean monthly flows and low-flow
statistics in Great Britain. [WGII 3.3.1]
Multi-model probabilistic approaches are preferable to using the
output of only one climate model, when assessing uncertainty
in the impact of climate change on water resources. Since the
TAR, several hydrological impact studies have used multi-model
climate inputs (e.g., Arnell (2004) at the global scale and Jasper
et al. (2004) at a river-basin scale), but studies incorporating
probabilistic assessments are rare. [WGII 3.3.1]
In many impacts studies, time-series of observed climate values
are adjusted by using the computed change in climate variables to
obtain scenarios that are consistent with present-day conditions.
These adjustments aim to minimise the impacts of the error
in climate modelling of the GCMs under the assumption that
the biases in climate modelling are of similar magnitude for
current and future time horizons. This is particularly important
for precipitation projections, where differences between the
observed values and those computed by climate models are
substantial. [WGII 3.3.1]
Changes in interannual or daily variability of climate variables
are often not taken into account in hydrological impact studies.
This leads to an underestimation of future floods and droughts
as well as water availability and irrigation water requirements.
[WGII 3.3.1] Selections of indicators and threshold values to
quantify the impact of climate change on freshwater resources
are also sources of uncertainty.
So as to overcome the mismatch of spatial grid scales between
GCM and hydrological processes, techniques have been
developed that downscale GCM outputs to a finer spatial
(and temporal) resolution. [WGI TAR Chapter 10] The main
assumption of these techniques is that the statistical relationships
identified for current climate will remain valid under changes in
future conditions. Downscaling techniques may allow modellers
to incorporate daily variability in future changes (e.g., DiazNieto and Wilby, 2005) and to apply a probabilistic framework
to produce information on future river flows for water resource
planning (Wilby and Harris, 2006). These approaches help
48
Section 3
to compare different sources of uncertainty affecting water
resource projections. [WGII 3.3.1]
Efforts to quantify the economic impacts of climate-related
changes in water resources are hampered by a lack of data
and by the fact that the estimates are highly sensitive to both
the estimation methods and the different assumptions used
regarding allocation of changes in water availability across
various types of water uses, e.g., between agricultural, urban or
instream uses (Changnon, 2005; Schlenker et al., 2005; Young,
2005). [WGII 3.5]
3.3 Water-related adaptation to climate
change: an overview
Water managers have long dealt with changing demands for water
resources. To date, water managers have typically assumed that
the natural resource base is reasonably constant over the medium
term and, therefore, that past hydrological experience provides
a good guide to future conditions. Climate change challenges
these conventional assumptions and may alter the reliability
of water management systems. [WGII 3.6.1] Management
responses to climate change include the development of new
approaches to system assessment and design, and non-structural
methods through such mechanisms as the European Union Water
Framework Directive. [WGII 12.2.2]
Table 3.4 summarises some supply-side and demand-side
adaptation options, designed to ensure supplies during average
and drought conditions. Supply-side options generally involve
increases in storage capacity or abstraction from water courses
and therefore may have adverse environmental consequences.
Demand-side options may lack practical effectiveness because
they rely on the cumulative actions of individuals. Some options
may be inconsistent with mitigation measures because they
involve high energy consumption, e.g., desalination, pumping.
A distinction is frequently made between autonomous and
planned adaptations. Autonomous adaptations are those that
do not constitute a conscious response to climate stimuli, but
result from changes to meet altered demands, objectives and
expectations which, whilst not deliberately designed to cope
with climate change, may lessen the consequences of that
change. Such adaptations are widespread in the water sector,
although with varying degrees of effectiveness in coping with
climate change (see Table 3.5). [WGII 3.6.1] In Latin America,
some autonomous adaptation practices have been put in place,
including the use of managing trans-basin diversions and the
optimisation of water use. [WGII 13.5.1.3] In Africa, local
communities and farmers have developed adaptation schemes to
forecast rainfall using accumulated experience. Farmers in the
Sahel also use traditional water harvesting systems to supplement
irrigation practices. [WGII 9.6.2.1, 9.5.1, Table 9.2]
Planned adaptations are the result of deliberate policy decisions
and specifically take climate change and variability into account,
Section 3
Linking climate change and water resources: impacts and responses
Table 3.4: Some adaptation options for water supply and demand (the list is not exhaustive). [WGII Table 3.5]
Supply-side
Demand-side
Prospecting and extraction of groundwater
Improvement of water-use efficiency by recycling water
Increasing storage capacity by building reservoirs and
dams
Desalination of sea water
Reduction in water demand for irrigation by changing the cropping calendar, crop
mix, irrigation method, and area planted
Reduction in water demand for irrigation by importing agricultural products, i.e.,
virtual water
Promotion of indigenous practices for sustainable water use
Expansion of rain-water storage
Removal of invasive non-native vegetation from riparian
areas
Water transfer
Expanded use of water markets to reallocate water to highly valued uses
Expanded use of economic incentives including metering and pricing to encourage
water conservation
and have so far been implemented infrequently. Water managers
in a few countries, including the Netherlands, Australia, the
UK, Germany, the USA and Bangladesh, have begun to address
directly the implications of climate change as part of their
standard flood and water supply management practices. [WGII
3.2, 3.6.5, 17.2.2] These adaptations have generally taken the
form of alterations to methods and procedures, such as design
standards and the calculation of climate change allowances.
For example, such adaptations have been implemented for
flood preparedness in the UK and the Netherlands (Klijn et
al., 2001; Richardson, 2002), for water supply in the UK
(Arnell and Delaney, 2006), and for water planning in general
in Bangladesh. [WGII 3.6.5, 17.2.2] Examples of ‘concrete’
actions in the water sector to adapt specifically and solely to a
changing climate are very rare. This is partly because climate
change may be only one of many drivers affecting strategies
and investment plans (and it may not be the most important
one over the short-term planning horizon), and partly due to
uncertainty in projections of future hydrological changes.
Adaptation to changes in water availability and quality will
have to be made, not only by water management agencies but
also by individual users of the water environment. These will
include industry, farmers (especially irrigators) and individual
consumers. Although there is much experience with adaptation
to changing demand and legislation, little is known about how
such organisations and individuals will be able to adapt to a
changing climate.
Table 3.5 outlines some of the adaptation measures, both
planned and autonomous, currently in use across the world, as
presented in the regional chapters in the WGII AR4. The table
is not exhaustive, and many individual measures can be used in
many locations.
There is high confidence that adaptation can reduce vulnerability,
especially in the short term. [WGII 17.2, 18.1, 18.5, 20.3, 20.8]
However, adaptive capacity is intimately connected to social
and economic development, but it is not evenly distributed
across and within societies. The poor, elderly, female, sick, and
indigenous populations typically have less capacity. [WGII 7.1,
7.2, 7.4, 17.3]
It is possible to define five different types of limits on adaptation
to the effects of climate change. [WGII 17.4.2]
(a) Physical or ecological: it may not be possible to prevent adverse
effects of climate change through either technical means or
institutional changes. For example, it may be impossible to
adapt where rivers dry up completely. [WGII 3.6.4]
(b) Technical, political or social: for example, it may be
difficult to find acceptable sites for new reservoirs, or for
water users to consume less. [WGII 3.6.4]
(c) Economic: an adaptation strategy may simply be too costly
in relation to the benefits achieved by its implementation.
(d) Cultural and institutional: these may include the
institutional context within which water management
operates, the low priority given to water management,
lack of co-ordination between agencies, tensions between
different scales, ineffective governance, and uncertainty
over future climate change (Ivey et al., 2004; Naess et
al., 2005; Crabbe and Robin, 2006); all act as institutional
constraints on adaptation. [WGII 3.6.4]
(e) Cognitive and informational: for example, water managers
may not recognise the challenge of climate change, or may
give it low priority compared with other challenges. A key
informational barrier is the lack of access to methodologies
to cope consistently and rigorously with climate change.
[WGII 17.4.2.4]
Climate change poses a conceptual challenge to water managers
by introducing uncertainty in future hydrological conditions.
It may also be very difficult to detect an underlying trend
(Wilby, 2006), meaning that adaptation decisions may have
to be made before it is clear how hydrological regimes may
actually be changing. Water management in the face of climate
change therefore needs to adopt a scenario-based approach
(Beuhler, 2003; Simonovic and Li, 2003). This is being used
in practice in countries such as the UK (Arnell and Delaney,
2006) and Australia (Dessai et al., 2005). However, there are
two problems. First, there are often large differences in impact
between scenarios, requiring that analyses be based on several
scenarios. Second, water managers in some countries demand
information on the likelihood of defined outcomes occurring
in order to make risk-based decisions (e.g., Jones and Page,
49
Section 3
Linking climate change and water resources: impacts and responses
Table 3.5: Some examples of adaptation in practice.
Region
Africa
Asia
Australia and
New Zealand
Europe
Adaptation measure
• Seasonal forecasts, their production, dissemination, uptake and integration in model-based
decision-making support systems
• Enhancing resilience to future periods of drought stress by improvements in present rainfed farming systems through improvements in the physical infrastructure including: water
harvesting systems; dam building; water conservation and agricultural practices; drip irrigation;
development of drought-resistant and early-maturing crop varieties and alternative crop and
hybrid varieties
Improvement to agricultural infrastructure including:
• pasture water supply
• irrigation systems and their efficiency
• use/storage of rain and snow water
• information exchange system on new technologies at national as well as regional and
international levels
• access by herders, fishers and farmers to timely weather forecasts (rainfall and temperature)
• Recycling and reuse of municipal wastewater e.g., Singapore
• Reduction of water wastage and leakage and use of market-oriented approaches to reduce
wasteful water use
• National Water Initiative
• Treatment plant to supply recycled water
• Reduce channel seepage and conservation measures
• Pipelines to replace open irrigation channels
• Improve water-use efficiency and quality
• Drought preparedness, new water pricing
• Installation of rainwater tanks
• Seawater desalination
Source
WGII 9.5, Table 9.2
•
WGII 12.5.1
WGII 14.5.1
Latin America
•
•
•
North America
•
Demand-side strategies such as household, industrial and agricultural water conservation,
repairing leaky municipal and irrigation water reservoirs in highland areas and dykes in lowland
areas
Expanded floodplain areas, emergency flood reservoirs, preserved areas for flood water and
flood warning systems, especially in flash floods
Supply-side measures such as impounding rivers to form instream reservoirs, wastewater
reuse and desalination systems and water pricing
Incorporation of regional and watershed-level strategies to adapt to climate change into plans
for integrated water management
Rainwater catchments and storage systems
‘Self organisation’ programmes for improving water supply systems in very poor communities
Water conservation practices, reuse of water, water recycling by modification of industrial
processes and optimisation of water use
Improved water conservation and conservation tillage
•
Investments in water conservation systems and new water supply and distribution facilities
•
Changing the policy of the US National Flood Insurance to reduce the risk of multiple flood
claims
Households with two flood-related claims now required to be elevated 2.5 cm above the 100year flood level, or to relocate
Flushing the drainage systems and replacing the trunk sewer systems to meet more extreme
5-year flood criteria
Directing roof runoff to lawns to encourage infiltration, and increasing depression and street
detention storage
A successful adaptation strategy that has already been used to counteract the effects of drying
of delta ponds involves managing water release from reservoirs to increase the probability of
ice-jam formation and related flooding
Flow regulation for hydro-electric production, harvesting strategies and methods of drinkingwater access
Strategies to deal with increased/decreased freshwater hazards (e.g., protective structures to
reduce flood risks or increase floods for aquatic systems
Desalination plants
Large storage reservoirs and improved water harvesting
Protection of groundwater, increasing rainwater harvesting and storage capacity, use of solar
distillation, management of storm water and allocation of groundwater recharge areas in the
islands
•
•
•
•
•
•
Polar regions
•
•
•
Small Islands
50
•
•
•
WGII 10.5,
Table 10.8
WGII 10.5.2
WGII 11.2,
Table 11.2, Box 11.2;
see Table 5.2 in this
volume
WGII 13.2.5.3,
Box 13.2, 13.5.1
WGII 14.2.4
WGII 15.6.2
WGII 15.2.2.2
WGII 16.4.1
Box 16.5
Linking climate change and water resources: impacts and responses
Section 3
2001). Techniques are therefore being developed to construct
probability distributions of specified outcomes, requiring that
assumptions be made about the probability distributions of
the key drivers of impact uncertainty (e.g., Wilby and Harris,
2006). [WGII 3.6.4]
A second approach to coping with uncertainty, referred to as
‘adaptive management’ (Stakhiv, 1998), involves the increased
use of water management measures that are relatively robust to
uncertainty. Such tools include measures to reduce the demand
for water and have been advocated as a means of minimising
the exposure of a system to climate change (e.g., in California:
Beuhler, 2003). Similarly, some resilient strategies for flood
management, e.g., allowing rivers to flood temporarily,
and reducing exposure to flood damage, are more robust to
uncertainty than traditional flood protection measures (Klijn et
al., 2004; Olsen, 2006). [WGII 3.6.4]
3.3.1
Integrated water resources management
Integrated water resources management (IWRM: see Footnote
17) should be an instrument to explore adaptation measures
to climate change, but so far it is in its infancy. Successful
integrated water management strategies include, among others:
capturing society’s views, reshaping planning processes, coordinating land and water resources management, recognising
water quantity and quality linkages, conjunctive use of surface
water and groundwater, protecting and restoring natural
systems, and including consideration of climate change. In
addition, integrated strategies explicitly address impediments
to the flow of information. A fully integrated approach is not
always needed but, rather, the appropriate scale for integration
will depend on the extent to which it facilitates effective
action in response to specific needs (Moench et al., 2003). In
particular, an integrated approach to water management could
help to resolve conflicts between competing water users.
In several places in the western USA, water managers and
various interest groups have been experimenting with methods
to promote consensus-based decision making. These efforts
include local watershed initiatives and state-led or federallysponsored efforts to incorporate stakeholder involvement
in planning processes (e.g., US Department of the Interior,
2005). Such initiatives can facilitate negotiations between
competing interest groups to achieve mutually satisfactory
problem solving that considers a wide range of factors. In the
case of large watersheds, such as the Colorado River Basin,
these factors cross several time- and space-scales (Table 3.6).
[WGII 3.6.1, Box 14.2]
Table 3.6: Cross-scale issues in the integrated water management of the Colorado River Basin (Pulwarty and Melis, 2001).
[WGII Table 3.4]
Temporal scale
Indeterminate
Long-term
Issue
Flow necessary to protect endangered species
Inter-basin allocation and allocation among basin states
Decadal
Year
Seasonal
Daily to monthly
Hourly
Spatial scale
Global
Regional
State
Municipal and communities
Upper basin delivery obligation
Lake Powell fill obligations to achieve equalisation with Lake Mead storage
Peak heating and cooling months
Flood control operations
Western Area Power Administration’s power generation
Climate influences, Grand Canyon National Park
Prior appropriation (e.g., Upper Colorado River Commission)
Different agreements on water marketing for within and out-of-state water districts
Watering schedules, treatment, domestic use
51
4
Climate change and water resources
in systems and sectors
Climate change and water resources in systems and sectors
Section 4
4.1 Ecosystems and biodiversity
4.1.1
Context
Temperature and moisture regimes are among the key variables
that determine the distribution, growth and productivity, and
reproduction of plants and animals. Changes in hydrology can
influence species in a variety of ways, but the most completely
understood processes are those that link moisture availability
with intrinsic thresholds that govern metabolic and reproductive
processes (Burkett et al., 2005). The changes in climate that are
anticipated in the coming decades will have diverse effects on
moisture availability, ranging from alterations in the timing and
volume of streamflow to the lowering of water levels in many
wetlands, the expansion of thermokarst lakes in the Arctic, and a
decline in mist water availability in tropical mountain forests.
Observed global trends in precipitation, humidity, drought and
runoff over the last century are summarised in WGI AR4 Chapter
3. Although changes in precipitation during the last century
indicate considerable regional variation [WGI Figure 3.14],
they also reveal some important and highly significant trends.
Precipitation increased generally in the Northern Hemisphere
from 1900 to 2005, but the tendency towards more widespread
drought increased concomitantly for many large regions of the
tropics and the Southern Hemisphere, notably the African Sahel
and southern Africa, Central America, south Asia and eastern
Australia. [WGI 3.3.5]
4.1.2
Projected changes in hydrology and
implications for global biodiversity
The IPCC Fourth Assessment Report estimates of global
warming vary in range from 0.5°C in the Southern Hemisphere
to 2°C in the northern polar region by 2030 for SRES scenarios
B1, A1 and A2, with B1 showing the highest warming. While
the models simulate global mean precipitation increases, there
is substantial spatial and temporal variation. General circulation
models (GCMs) project an increase in precipitation at high
latitudes, although the amount of that increase varies between
models, and decreases in precipitation over many sub-tropical
and mid-latitude areas in both hemispheres. [WGI Figures
10.8 and 10.12] Precipitation during the coming decades is
projected to be more concentrated into more intense events,
with longer periods of little precipitation in between. [WGI
10.3.6.1] The increase in the number of consecutive dry days is
projected to be most significant in North and Central America,
the Caribbean, north-eastern and south-western South America,
southern Europe and the Mediterranean, southern Africa and
western Australia. [WGI Figure 10.18] Impacts of warming and
changes in precipitation patterns in tropical and sub-tropical
regions have important implications for global biodiversity,
because species diversity generally decreases with distance
away from the Equator.
The changes in hydrology that are projected by WGI AR4 for
the 21st century (see Section 2) will be very likely to impact
biodiversity on every continent. Impacts on species have
already been detected in most regions of the world. [WGII 1.3,
4.2] A review of 143 published studies by Root et al. (2003)
indicates that animals and plants are already showing discernible
changes consistent with the climatic trends of the 20th century.
Approximately 80% of the changes were consistent with
observed temperature change, but it should be recognised that
temperature can also exert its influence on species through
changes in moisture availability. [WGII 1.4.1]
Ecosystem responses to changes in hydrology often involve
complex interactions of biotic and abiotic processes. The
assemblages of species in ecological communities reflect the
fact that these interactions and responses are often non-linear,
which increases the difficulty of projecting specific ecological
outcomes. Since the timing of responses is not always
synchronous in species from different taxonomic groups,
there may be a decoupling of species from their food sources,
a disruption of symbiotic or facilitative relationships between
species, and changes in competition between species. Owing
to a combination of differential responses between species and
interactions that could theoretically occur at any point in a food
web, some of the ecological communities existing today could
easily be disaggregated in the future (Root and Schneider, 2002;
Burkett et al., 2005). [WGII 1.3.5.5, 4.2.2, 4.4]
Due to the combined effects of temperature and water stress,
the extinction of some amphibians and other aquatic species is
projected in Costa Rica, Spain and Australia (Pounds et al., 2006).
[WGII Table 4.1] Drying of wetlands in the Sahel will affect
the migration success of birds that use the Sahelian wetlands as
stopovers in their migration to Northern Hemisphere breeding
sites. In southern Africa, unprecedented levels of extinctions
in both plant and animal species are envisaged. [WGII Table
9.1] In montane forests, many species depend on mist as their
source of water: global warming will raise the cloud base and
affect those species dependent on this resource. [WGII 13.4.1]
Of all ecosystems, however, freshwater aquatic ecosystems
appear to have the highest proportion of species threatened
with extinction by climate change (Millennium Ecosystem
Assessment, 2005b). [WGII 3.5.1]
4.1.3
Impacts of changes in hydrology on major ecosystem types
4.1.3.1 Lakes and streams
Impacts of global warming on lakes include an extended
growing period at high latitudes, intensified stratification and
nutrient loss from surface waters, decreased hypolimnetic
oxygen (below the thermocline) in deep, stratified lakes, and
expansion in range for many invasive aquatic weeds. Water
levels are expected to increase in lakes at high latitudes,
where climate models indicate increased precipitation, while
water levels at mid- and low latitudes are projected to decline.
Endorheic (terminal or closed) lakes are most vulnerable to
a change in climate because of their sensitivity to changes in
the balance of inflows and evaporation. Changes in inflows to
such lakes can have very substantial effects and, under some
55
Climate change and water resources in systems and sectors
climatic conditions, they may disappear entirely. The Aral
Sea, for example, has been significantly reduced by increased
abstractions of irrigation water upstream; and Qinghai Lake in
China has shrunk following a fall in catchment precipitation.
[WGII TAR 4.3.7]
The duration of ice cover in lakes and rivers at mid- to high
latitudes has decreased by approximately two weeks during the
past century in the Northern Hemisphere. [WGI TAR SPM]
Increases in summer water temperature can increase anoxia
in stratified lakes, increase the rate of phosphorus releases
from lake-bottom sediments, and cause algal blooms that
restructure the aquatic food web. [WGII 4.4.8] A unit increase
in temperature in tropical lakes causes a proportionately higher
density differential as compared with colder temperate lakes.
Thus, projected tropical temperatures [WGI Chapters 10 and
11] will lead to strong thermal stratification, causing anoxia
in deep layers of lakes and nutrient depletion in shallow lake
waters. Reduced oxygen concentrations will generally reduce
aquatic species diversity, especially in cases where water quality
is impaired by eutrophication. [CCB 4.4]
Reduced oxygen concentrations tend to alter biotic assemblages,
biogeochemistry and the overall productivity of lakes and
streams. The thermal optima for many mid- to high-latitude
cold-water taxa are lower than 20°C. Species extinctions are
expected when warm summer temperatures and anoxia eliminate
deep cold-water refugia. In the southern Great Plains of the
USA, water temperatures are already approaching lethal limits
for many native stream fish. Organic matter decomposition
rates increase with temperature, thereby shortening the period
over which detritus is available to aquatic invertebrates. [CCB
6.2] Invasive alien species represent a major threat to native
biodiversity in aquatic ecosystems. [WGII 4.2.2] The rise in
global temperature will tend to extend polewards the ranges of
many invasive aquatic plants, such as Eichhornia and Salvinia.
[RICC 2.3.6]
Effects of warming on riverine systems may be strongest in
humid regions, where flows are less variable and biological
interactions control the abundance of organisms. Drying of
stream-beds and lakes for extended periods could reduce
ecosystem productivity because of the restriction on aquatic
habitat, combined with lowered water quality via increased
oxygen deficits and pollutant concentrations. In semi-arid
parts of the world, reductions in seasonal streamflow and
complete drying up of lakes (such as in the Sahel of Africa)
can have profound effects on ecosystem services, including the
maintenance of biodiversity. [CCB 6.7]
Currently, species richness is highest in freshwater systems
in central Europe and decreases to the north and south due
to periodic droughts and salinisation (Declerck et al. 2005).
Ensemble GCM runs for the IPCC AR4 indicate a south–north
contrast in precipitation, with increases in the north and decreases
in the south. [WGI 11.3.3.2] An increase in projected runoff and
lower risk of drought could benefit the fauna of aquatic systems
56
Section 4
in northern Europe, while decreased water availability in the
south could have the opposite effect (Álvarez Cobelas et al.,
2005). [WGII 12.4.6]
4.1.3.2 Freshwater wetlands
The high degree of variability in the structure of wetland systems
is due mainly to their individual hydrology, varying from
peatland bogs in high-latitude boreal forests, through tropical
monsoonal wetlands (e.g., the Kakadu wetlands, Australia), to
high-altitude wetlands in the Tibetan and Andean mountains.
Climate change will have its most pronounced effects on
inland freshwater wetlands through altered precipitation and
more frequent or intense disturbance events (droughts, storms,
floods). Relatively small increases in precipitation variability
can significantly affect wetland plants and animals at different
stages of their life cycle (Keddy, 2000). [WGII 4.4.8] Generally,
climatic warming is expected to start a drying trend in wetland
ecosystems. This largely indirect influence of climate change,
leading to alterations in the water level, would be the main
agent in wetland ecosystem change and would overshadow the
impacts of rising temperature and longer growing seasons in
boreal and sub-Arctic peatlands (Gorham, 1991). Monsoonal
areas are more likely to be affected by more intense rain events
over shorter rainy seasons, exacerbating flooding and erosion in
catchments and the wetlands themselves. [WGII TAR 5.8.3]
Most wetland processes are dependent on catchment-level
hydrology, which can be altered by changes in land use as well
as surface water resource management practices. [WGII TAR
5.ES] Recharge of local and regional groundwater systems, the
position of the wetland relative to the local topography, and the
gradient of larger regional groundwater systems are also critical
factors in determining the variability and stability of moisture
storage in wetlands in climatic zones where precipitation does not
greatly exceed evaporation (Winter and Woo, 1990). Changes in
recharge external to the wetland may be as important to the fate
of the wetland under changing climatic conditions, as are the
changes in direct precipitation and evaporation on the wetland
itself (Woo et al., 1993). [WGII TAR 5.8.2.1] Thus, it may be
very difficult, if not impossible, to adapt to the consequences
of projected changes in water availability. [WGII TAR 5.8.4]
Due, in part, to their limited capacity for adaptation, wetlands
are considered to be among the ecosystems most vulnerable to
climate change. [WGII 4.4.8]
Wetlands are often biodiversity hotspots. Many have world
conservation status (Ramsar sites, World Heritage sites). Their
loss could lead to significant extinctions, especially among
amphibians and aquatic reptiles. [WGII 4.4.8] The TAR
identified Arctic and sub-Arctic ombrotrophic (‘cloud-fed’)
bogs and depressional wetlands with small catchments as the
most vulnerable aquatic systems to climate change. [WGII TAR
5.8.5] The more recent AR4, however, suggests a very high
degree of vulnerability for many additional wetland types, such
as monsoonal wetlands in India and Australia, boreal peatlands,
North America’s prairie pothole wetlands and African Great
Lake wetlands. [WGII 4.4.8, 4.4.10] The seasonal migration
patterns and routes of many wetland species will have to change;
Section 4
otherwise some species will be threatened with extinction.
[WGII 4.4.8] For key habitats, small-scale restoration may be
possible, if sufficient water is available. [WGII TAR 5.8.4]
Due to changes in hydrology associated with atmospheric
warming, the area of wetland habitat has increased in some
regions. In the Arctic region, thawing of permafrost is giving
rise to new wetlands. [WGII 1.3] Thermokarst features, which
result from the melting of ground ice in a region underlain
by permafrost, can displace Arctic biota through either oversaturation or drying (Hinzman et al., 2005; Walsh et al., 2005).
Extensive thermokarst development has been discovered in
North America near Council, Alaska (Yoshikawa and Hinzman,
2003) and in central Yakutia (Gavriliev and Efremov, 2003).
[WGI 4.7.2.3] Initially, permafrost thaw forms depressions
for new wetlands and ponds that are interconnected by new
drainage features. As the permafrost thaws further, surface
waters drain into groundwater systems, leading to losses in
freshwater habitat. [WGII 15.4.1.3] Warming may have already
caused the loss of wetland area as lakes on the Yukon Delta
expanded during the past century (Coleman and Huh, 2004).
[WGII 15.6.2]
Small increases in the variability in precipitation regimes can
significantly affect wetland plants and animals (Keddy, 2000;
Burkett and Kusler, 2000). Biodiversity in seasonal wetlands,
such as vernal pools, can be strongly impacted by changes in
precipitation and soil moisture (Bauder, 2005). In monsoonal
regions, prolonged dry periods promote terrestrialisation of
wetlands, as witnessed in Keoladeo National Park (Chauhan
and Gopal, 2001). [WGII 4.4.8]
4.1.3.3 Coasts and estuaries
Changes in the timing and volume of freshwater runoff will
affect salinity, sediment and nutrient availability, and moisture
regimes in coastal ecosystems. Climate change can affect
each of these variables by altering precipitation and locally
driven runoff or, more importantly, runoff from watersheds
that drain into the coastal zone. [WGII 6.4.1.3] Hydrology
has a strong influence on the distribution of coastal wetland
plant communities, which typically grade inland from salt, to
brackish, to freshwater species. [WGII 6.4.1.4]
The effects of sea-level rise on coastal landforms vary
among coastal regions because the rate of sea-level rise is
not spatially uniform [WGI 5.5.2] and because some coastal
regions experience uplift or subsidence due to processes that
are independent of climate change. Such processes include
groundwater withdrawals, oil and gas extraction, and isostacy
(adjustment of the Earth’s surface on geological timescales
to changes in surface mass; e.g., due to changes in ice sheet
mass following the last deglaciation). In addition to changes in
elevation along the coast, factors arising inland can influence
the net effect of sea-level rise on coastal ecosystems. The
natural ecosystems within watersheds have been fragmented
and the downstream flow of water, sediment and nutrients to
the coast has been disrupted (Nilsson et al., 2005). Land-use
Climate change and water resources in systems and sectors
change and hydrological modifications have had downstream
impacts, in addition to localised influences, including human
development on the coast. Erosion has increased the sediment
load reaching the coast; for example, suspended loads in the
Huanghe (Yellow) River have increased 2–10 times over the
past 2,000 years (Jiongxin, 2003). In contrast, damming and
channelisation have greatly reduced the supply of sediments
to the coast on other rivers through the retention of sediment
in dams (Syvistki et al., 2005), and this effect will probably
dominate during the 21st century. [WGII 6.4]
Climate model ensemble runs by Milly et al. (2005) indicate
that climate change during the next 50–100 years will increase
discharges to coastal waters in the Arctic, in northern Argentina
and southern Brazil, parts of the Indian sub-continent and
China, while reduced discharges to coastal waters are suggested
in southern Argentina and Chile, western Australia, western and
southern Africa, and in the Mediterranean Basin. [WGII 6.3.2;
see Figure 2.10 in this volume] If river discharge decreases, the
salinity of coastal estuaries and wetlands is expected to increase
and the amount of sediments and nutrients delivered to the
coast to decrease. In coastal areas where streamflow decreases,
salinity will tend to advance upstream, thereby altering the
zonation of plant and animal species as well as the availability
of freshwater for human use. The increased salinity of coastal
waters since 1950 has contributed to the decline of cabbage
palm forests in Florida (Williams et al., 1999) and bald cypress
forests in Louisiana (Krauss et al., 2000). Increasing salinity
has also played a role in the expansion of mangroves into
adjacent marshes in the Florida Everglades (Ross et al., 2000)
and throughout south-eastern Australia during the past 50 years
(Saintilan and Williams, 1999). [WGII 6.4.1.4] Saltwater
intrusion as a result of a combination of sea-level rise, decreases
in river flows and increased drought frequency are expected to
alter estuarine-dependent coastal fisheries during this century in
parts of Africa, Australia and Asia. [WGII 6.4.1.3, 9.4.4, 10.4.1,
11.4.2]
Deltaic coasts are particularly vulnerable to changes in runoff
and sediment transport, which affect the ability of a delta to
cope with the physical impacts of climatic change. In Asia,
where human activities have led to increased sediment loads
of major rivers in the past, the construction of upstream dams
is now depleting the supply of sediments to many deltas, with
increased coastal erosion becoming a widespread consequence
(Li et al., 2004; Syvitski et al., 2005; Ericson et al., 2006).
[WGII 6.2.3, 6.4.1] In the subsiding Mississippi River deltaic
plain of south-east Louisiana, sediment starvation due to human
intervention in deltaic processes and concurrent increases in the
salinity and water levels of coastal marshes occurred so rapidly
that 1,565 km2 of intertidal coastal marshes and adjacent coastal
lowlands were converted to open water between 1978 and 2000
(Barras et al., 2003). [WGII 6.4.1]
Some of the greatest potential impacts of climate change
on estuaries may result from changes in physical mixing
characteristics caused by changes in freshwater runoff (Scavia
57
Climate change and water resources in systems and sectors
et al., 2002). Freshwater inflows into estuaries influence water
residence time, nutrient delivery, vertical stratification, salinity,
and control of phytoplankton growth rates (Moore et al.,
1997). Changes in river discharges into shallow near-shore
marine environments will lead to changes in turbidity, salinity,
stratification and nutrient availability (Justic et al., 2005).
[WGII 6.4.1.3]
4.1.3.4 Mountain ecosystems
The zonation of ecosystems along mountain gradients is
mediated by temperature and soil moisture. Recent studies
(Williams et al., 2003; Pounds and Puschendorf, 2004;
Andreone et al., 2005; Pounds et al., 2006) have shown the
disproportionate risk of extinctions in mountain ecosystems
and, in particular, among endemic species. [WGII 4.4.7] Many
species of amphibians, small mammals, fish, birds and plants
are highly vulnerable to the ongoing and projected changes
in climate that alter their highly specialised mountain niche.
[WGII 1.3.5.2, 4.4.7, 9.4.5]
In many snowmelt-dominated watersheds, temperature
increase has shifted the magnitude and timing of hydrological
events. A trend towards earlier peak spring streamflow and
increased winter base flows has been observed in North
America and Eurasia. [WGII 1.3.2] A greater fraction of
annual precipitation is falling as rain rather than snow at
74% of the weather stations studied in the western mountains
of the USA between 1949 and 2004 (Knowles et al., 2006).
Since the 1970s, winter snow depth and spring snow cover
have decreased in Canada, particularly in the west, where air
temperatures have consistently increased (Brown and Braaten,
1998). Spring and summer snow cover is decreasing in the
western USA (Groisman et al., 2004). The April 1st snow water
equivalent (SWE) has decreased by 15–30% since 1950 in the
western mountains of North America, particularly at lower
elevations in spring, primarily due to warming rather than to
changes in precipitation (Mote et al., 2005). Streamflow peaks
in the snowmelt-dominated western mountains of the USA
occurred 1–4 weeks earlier in 2002 than in 1948 (Stewart et
al., 2005). [WGII 14.2.1]
The duration and depth of snow cover, often correlated with
mean temperature and precipitation (Keller et al., 2005;
Monson et al., 2006), is a key factor in many alpine ecosystems
(Körner, 1999). Missing snow cover exposes plants and animals
to frost, and influences water supply in spring (Keller et al.,
2005). If animal movements are disrupted by changing snow
patterns, as has been found in Colorado (Inouye et al., 2000),
increased wildlife mortality may result through a mismatch
between wildlife and environment. [WGII 4.4.7] For each 1°C
of temperature increase, the duration of snow cover is expected
to decline by several weeks at mid-elevations in the European
Alps. It is virtually certain that European mountain flora will
undergo major changes in response to climate change, with
changes in snow-cover duration being a more important driver
than the direct effects of temperature on animal metabolism.
[WGII 12.4.3]
58
Section 4
Changing runoff from glacier melt has significant effects
on ecosystem services. Biota of small-watershed streams
sustained by glacial melt are highly vulnerable to extirpation.
[WGII 1.3.1, 3.2, 3.4.3]
4.1.3.5 Forests, savannas and grasslands
The availability of water is a key factor in the restructuring of
forest and grassland systems as the climate warms. Climate
change is known to alter the likelihood of increased wildfire
size and frequency, while also inducing stress in trees, which
indirectly exacerbates the effects of these disturbances. Many
forest ecosystems in the tropics, high latitudes and high
altitudes are becoming increasingly susceptible to drought and
associated changes in fire, pests and diseases. [WGII Chapter
4, 5.1.2, 13.4] It has been estimated that up to 40% of the
Amazonian forests could be affected by even slight decreases
in precipitation (Rowell and Moore, 2000). Multi-model GCM
simulations of precipitation changes over South America
during the next 100 years show a substantial (20% or more)
decrease in June, July and August precipitation in the Amazon
Basin, but a slight increase (approximately 5%) in December,
January and February. [WGI 11.6.3.2] These projected changes
in precipitation, coupled with increased temperature, portend a
replacement of some Amazonian forests by ecosystems that have
more resistance to the multiple stresses caused by temperature
increase, droughts and fires. [WGII 13.4.2]
Increases in drought conditions in several regions (Europe,
parts of Latin America) during the growing season are
projected to accompany increasing summer temperatures and
precipitation declines, with widespread effects on forest net
ecosystem productivity. Effects of drought on forests include
mortality due to disease, drought stress and pests; a reduction
in resilience; and biotic feedbacks that vary from site to site.
[WGII 4.4.5] In some regions, forests are projected to replace
other vegetation types, such as tundra and grasslands, and the
availability of water can be just as important as temperature and
CO2-enrichment effects on photosynthesis. [WGII 4.4.3, 4.4.5]
Numerous studies have evaluated the direct CO2 fertilisation
impact and warming effects on dominant forest and grassland
types. Studies involving a wide range of woody and herbaceous
species suggest that enhancements in photosynthesis due
to projected CO2 enrichment will be dependent upon water
availability. [WGII 4.4.3] Higher-order effects of CO2
enrichment in forests and savannas can have important
feedbacks on water resources. For example, atmospheric CO2
enrichment can have adverse effects on the nutritional value of
litter in streams (Tuchman et al., 2003), and soil water balance
can be strongly influenced by elevated CO2 in most grassland
types. [WGII 4.4.10] Grassland and savanna productivity is
highly sensitive to precipitation variability. In assessments of
tall-grass prairie productivity, for example, increased rainfall
variability was more significant than rainfall amount, with a
50% increase in dry-spell duration causing a 10% reduction in
net primary productivity (Fay et al., 2003a). [WGII 4.4.3]
Climate change and water resources in systems and sectors
Section 4
4.2 Agriculture and food security, land
iiiiiiiuse and forestry
4.2.1
Context
The productivity of agricultural, forestry and fisheries systems
depends critically on the temporal and spatial distribution of
precipitation and evaporation, as well as, especially for crops,
on the availability of freshwater resources for irrigation. [WGII
5.2.1] Production systems in marginal areas with respect to water
face increased climatic vulnerability and risk under climate
change, due to factors that include, for instance, degradation
of land resources through soil erosion, over-extraction of
groundwater and associated salinisation, and over-grazing of
dryland (FAO, 2003). [WGII 5.2.2] Smallholder agriculture in
such marginal areas is especially vulnerable to climate change
and variability, and socio-economic stressors often compound
already difficult environmental conditions. [WGII 5.2.2, Table
5.2, Box 5.3] In forests, fires and insect outbreaks linked to the
frequency of extreme events have been shown to increase climate
vulnerability. In fisheries, water pollution and changes in water
resources also increase vulnerability and risk. [WGII 5.2.2]
4.2.1.1 Agriculture and food security
Water plays a crucial role in food production regionally
and worldwide. On the one hand, more than 80% of global
agricultural land is rain-fed; in these regions, crop productivity
depends solely on sufficient precipitation to meet evaporative
demand and associated soil moisture distribution (FAO, 2003).
[WGII 5.4.1.2] Where these variables are limited by climate,
such as in arid and semi-arid regions in the tropics and subtropics, as well as in Mediterranean-type regions in Europe,
Australia and South America, agricultural production is very
vulnerable to climate change (FAO, 2003). On the other hand,
global food production depends on water not only in the form
of precipitation but also, and critically so, in the form of
available water resources for irrigation. Indeed, irrigated land,
representing a mere 18% of global agricultural land, produces
1 billion tonnes of grain annually, or about half the world’s total
supply; this is because irrigated crops yield on average 2–3
times more than their rain-fed counterparts19 (FAO, 2003).
While too little water leads to vulnerability of production,
too much water can also have deleterious effects on crop
productivity, either directly, e.g., by affecting soil properties
and by damaging plant growth, or indirectly, e.g., by harming or
delaying necessary farm operations. Heavy precipitation events,
excessive soil moisture and flooding disrupt food production
and rural livelihoods worldwide (Rosenzweig et al., 2002).
[WGII 5.4.2.1]
By critically affecting crop productivity and food production,
in addition to being a necessity in food preparation processes,
water plays a critical role in food security. Currently, 850 million
19
people in the world are still undernourished (FAO, 2003). [WGII
5.3.2.1, 5.6.5] Socio-economic pressures over the next several
decades will lead to increased competition between irrigation
needs and demand from non-agricultural sectors, potentially
reducing the availability and quality of water resources for
food. [WGII 3.3.2] Recent studies indicate that it is unlikely
that the Millennium Development Goal (MDG) for hunger will
be met by 2015. [WGII 5.6.5] At the same time, during this
century, climate change may further reduce water availability
for global food production, as a result of projected mean changes
in temperature and precipitation regimes, as well as due to
projected increases in the frequency of extreme events, such as
droughts and flooding (Rosenzweig et al., 2002). [WGII 5.6.5]
Climate impacts assessments of food production are, in general,
critically dependent upon the specifics of the GCM precipitation
projections used. [WGII 5.4.1.2] A wide range of precipitation
scenarios is currently available. In general, assessments using
scenarios of reduced regional precipitation typically result in
negative crop production signals, and vice versa. Projections of
increased aridity in several Mediterranean-type environments
(Europe, Australia and South America), as well as in marginal
arid and semi-arid tropical regions, especially sub-Saharan
Africa, appear to be robust across models (see Figure 2.10).
These regions face increased vulnerability under climate
change, as shown in Figure 4.1. [WGII 5.3.1]
4.2.1.2 Land use and forest ecosystems
Forest ecosystems occupy roughly 4 billion ha of land, an area
comparable to that used by crops and pastures combined. Of this
land, only about 200 million ha are used for commercial forestry
production globally (FAO, 2003). [WGII 4.4.5, 5.1.1, 5.4.5]
Forests are key determinants of water supply, quality and
quantity, in both developing and developed countries. The
importance of forests as watersheds may increase substantially
in the next few decades, as freshwater resources become
increasingly scarce, particularly in developing countries
(Mountain Agenda, 1997; Liniger and Weingartner, 1998).
[LULUCF 2.5.1.1.4; WGII 4.1.1]
Forests contribute to the regional water cycle, with large
potential effects of land-use changes on local and regional
climates (Harding, 1992; Lean et al., 1996). On the other hand,
forest protection can have drought and flood mitigation benefits,
especially in the tropics (Kramer et al., 1997; Pattanayak and
Kramer, 2000). [LULUCF 2.5.1.1.6]
Afforestation and reforestation may increase humidity, lower
temperature and increase rainfall in the regions affected
(Harding, 1992; Blythe et al., 1994); deforestation can instead
lead to decreased local rainfall and increased temperature. In
Amazonia and Asia, deforestation may lead to new climate
conditions unsuitable for successful regeneration of rainforest
species (Chan, 1986; Gash and Shuttleworth, 1991; MeherHomji, 1992). [LULUCF 2.5.1.1.6]
See Section 1.3 for a discussion of the interrelationships between irrigation, climate change and groundwater recharge. This is also mentioned
in Sections 5.1.3 (on Africa) and 5.2.3 (on Asia).
59
Section 4
Climate change and water resources in systems and sectors
Forest ecosystems are differentially sensitive to climatic change
(e.g., Kirschbaum and Fischlin, 1996; Sala et al., 2000; Gitay et
al., 2001), with temperature-limited biomes being sensitive to
impacts of warming, and water-limited biomes being sensitive
to increasing levels of drought. Some, such as fire-dependent
ecosystems, may change rapidly in response to climate and
other environmental changes (Scheffer et al., 2001; Sankaran et
al., 2005). [WGII 4.1, 4.4.5]
Forest ecosystems, and the biodiversity associated with them,
may be particularly at risk in Africa, due to a combination of
socio-economic pressures, and land-use and climate-change
factors. [WGII 4.2] By 2100, negative impacts across about
25% of Africa (especially southern and western Africa) may
cause a decline in both water quality and ecosystem goods
and services. [WGII 4.ES, 4.4.8] Indeed, changes in a variety
of ecosystems are already being detected and documented,
particularly in southern Africa. [WGII 9.2.1.4]
4.2.2
Observations
4.2.2.1 Climate impacts and water
Although agriculture and forestry are known to be highly
dependent on climate, evidence of observed changes related to
regional climate changes, and specifically to water, is difficult
to find. Agriculture and forestry are also strongly influenced
by non-climate factors, especially management practices and
technological changes (Easterling, 2003) on local and regional
scales, as well as market prices and policies related to subsidies.
[WGII 1.3.6]
Although responses to recent climate change are difficult to
identify in human systems, due to multiple non-climate driving
forces and the existence of adaptation, effects have been
detected in forestry and a few agricultural systems. Changes in
several aspects of the human health system have been related
to recent warming. Adaptation to recent warming is beginning
to be systematically documented. In comparison with other
factors, recent warming has been of limited consequence in
agriculture and forestry. A significant advance in phenology,
however, has been observed for agriculture and forestry in
large parts of the Northern Hemisphere, with limited responses
in crop management. The lengthening of the growing season
has contributed to an observed increase in forest productivity
in many regions, while warmer and drier conditions are partly
responsible for reduced forest productivity and increased forest
fires in North America and the Mediterranean Basin. Both
agriculture and forestry have shown vulnerability to recent trends
in heatwaves, droughts and floods. [WGII 1.3.6, 1.3.9, 5.2]
4.2.2.2 Atmospheric CO2 and water dynamics
The effects of elevated atmospheric CO2 on plant function may
have important implications for water resources, since leaflevel water-use efficiency increases due to increased stomatal
resistance as compared to current concentrations. For C3
plant species (including most food crops), the CO2 effect may
be relatively greater for crops that are under moisture stress,
compared to well-irrigated crops. [WGII TAR 5.3.3.1]
60
However, the large-scale implications of CO2–water
interactions (i.e., at canopy, field and regional level) are highly
uncertain. In general, it is recognised that the positive effects of
elevated CO2 on plant water relations are expected to be offset
by increased evaporative demand under warmer temperatures.
[WGII TAR 5.3.3.1]
Many recent studies confirm and extend TAR findings that
temperature and precipitation changes in future decades will
modify, and often limit, direct CO2 effects on plants. For
instance, high temperatures during flowering may lower CO2
effects by reducing grain number, size and quality (Thomas et
al., 2003; Baker et al., 2004; Caldwell et al., 2005). Likewise,
increased water demand under warming may reduce the expected
positive CO2 effects. Rain-fed wheat grown at 450 ppm CO2
shows grain yield increases up to 0.8°C warming, but yields then
decline beyond 1.5°C warming; additional irrigation is needed
to counterbalance these negative effects. [WGII 5.4.1.2]
Finally, plant physiologists and crop modellers alike recognise
that the effects of elevated CO2, measured in experimental
settings and implemented in models, may overestimate actual
field and farm-level responses. This is due to many limiting
factors that typically operate at the field level, such as pests,
weeds, competition for resources, soil water and air quality.
These critical factors are poorly investigated in large-scale
experimental settings, and are thus not well integrated into the
leading plant growth models. Understanding the key dynamics
characterising the interactions of elevated CO2 with climate,
soil and water quality, pests, weeds and diseases, climate
variability and ecosystem vulnerability remains a priority for
understanding the future impacts of climate change on managed
systems. [WGII 5.4.1, 5.8.2]
4.2.3
Projections
Changes in water demand and availability under climate change
will significantly affect agricultural activities and food security,
forestry and fisheries in the 21st century. On the one hand,
changes in evaporation:precipitation ratios will modify plant
water demand with respect to a baseline with no climate change.
On the other hand, modified patterns of precipitation and storage
cycles at the watershed scale will change the seasonal, annual
and interannual availability of water for terrestrial and aquatic
agro-ecosystems (FAO, 2003). Climate changes increase
irrigation demand in the majority of world regions due to a
combination of decreased rainfall and increased evaporation
arising from increased temperatures. [WGII 5.8.1]
It is expected that projected changes in the frequency and
severity of extreme climate events, such as increased frequency
of heat stress, droughts and flooding, will have significant
consequences on food, forestry (and the risk of forest fires) and
other agro-ecosystem production, over and above the impacts
of changes in mean variables alone. [WGII 5.ES] In particular,
more than 90% of simulations predict increased droughts in the
sub-tropics by the end of the 21st century [WGI SPM], while
increased extremes in precipitation are projected in the major
Section 4
agricultural production areas of southern and eastern Asia,
eastern Australia and northern Europe. [WGI 11.3, 11.4, 11.7]
It should be noted that climate change impact models for food,
forest products and fibre do not yet include these recent findings
on the projected patterns of precipitation change; negative
impacts are projected to be worse than currently computed,
once the effects of extremes on productivity are included.
[WGII 5.4.1, 5.4.2]
Percentage changes in annual mean runoff are indicative of
the mean water availability for vegetation cover. Projected
changes between now and 2100 [WGII Chapter 3] show some
consistent patterns: increases in high latitudes and the wet
tropics, and decreases in mid-latitudes and some parts of the
dry tropics (Figure 4.1b). Declines in water availability are
indicative of increased water stress, indicating, in particular,
a worsening in regions where water for production is already
a scarce commodity (e.g., in the Mediterranean Basin, Central
America and sub-tropical regions of Africa and Australia, see
Figure 4.1b). [WGII 5.3.1]
Finally, it may be important to recognise that production
systems and water resources will be critically shaped in the
coming decades by the concurrent interactions of socioeconomic and climate drivers. For instance, increased demand
for irrigation water in agriculture will depend both on changed
climatic conditions and on increased demand for food by a
growing population; in addition, water availability for forest
productivity will depend on both climatic drivers and critical
anthropogenic impacts, particularly deforestation in tropical
zones. In the Amazon Basin, for instance, a combination of
deforestation and increased fragmentation may trigger severe
droughts over and above the climate signal, leading to increased
fire danger. [WGII 5.3.2.2]
Climate change and water resources in systems and sectors
4.2.3.1 Crops
In general, while moderate warming in high-latitude regions
would benefit crop and pasture yields, even slight warming in
low-latitude areas, or areas that are seasonally dry, would have
a detrimental effect on yields. Modelling results for a range of
sites show that, in high-latitude regions, moderate to medium
increases in local temperature (1–3°C), along with associated
CO2 increases and rainfall changes, can have small, beneficial
impacts on crop yields. However, in low-latitude regions, even
moderate temperature increases (1–2°C) are likely to have
negative yield impacts for major cereals. Further warming has
increasingly negative impacts in all regions. [WGII 5.ES]
Regions where agriculture is currently a marginal enterprise,
largely due to a combination of poor soils, water scarcity and
rural poverty, may suffer increasingly as a result of climate
change impacts on water. As a result, even small changes in
climate will increase the number of people at risk of hunger,
with the impact being particularly great in sub-Saharan Africa.
[WGII 5.ES]
Increases in the frequency of climate extremes may lower crop
yields beyond the impacts of mean climate change. Simulation
studies since the TAR have considered specific aspects of
increased climate variability within climate change scenarios.
Rosenzweig et al. (2002) computed that, under scenarios of
increased heavy precipitation, production losses due to excessive
soil moisture (already significant today) would double in the
USA to US$3 billion/yr in 2030. In Bangladesh, the risk of crop
losses is projected to increase due to higher flood frequency
under climate change. Finally, climate change impact studies
that incorporate higher rainfall intensity indicate an increased
risk of soil erosion; in arid and semi-arid regions, high rainfall
intensity may be associated with a higher possibility of
Figure 4.1: (a) Current suitability for rain-fed crops (excluding forest ecosystems) (after Fischer et al., 2002b). SI = suitability
index [WGII Figure 5.1a]; (b) ensemble mean percentage projected change in annual mean runoff between the present
(1980–1999) and 2090–2099. [Based on SYR Figure 3.5]
61
Climate change and water resources in systems and sectors
salinisation, due to increased loss of water past the crop root
zone. [WGII 5.4.2.1]
Impacts of climate change on irrigation water requirements
may be large. A few new studies have further quantified the
impacts of climate change on regional and global irrigation
requirements, irrespective of the positive effects of elevated
CO2 on crop water-use efficiency. Döll (2002), in considering
the direct impacts of climate change on crop evaporative
demand, but without any CO2 effects, estimated an increase in
net crop irrigation requirements (i.e., net of transpiration losses)
of between 5% and 8% globally by 2070, with larger regional
signals (e.g., +15%) in south-east Asia. [WGII 5.4.2.1]
Fischer et al. (2006), in a study that included positive CO2 effects
on crop water-use efficiency, computed increases in global net
irrigation requirements of 20% by 2080, with larger impacts
in developed versus developing regions, due to both increased
evaporative demands and longer growing seasons under
climate change. Fischer et al. (2006) and Arnell et al. (2004)
also projected increases in water stress (measured as the ratio
of irrigation withdrawals to renewable water resources) in the
Middle East and south-east Asia. Recent regional studies have
likewise underlined critical climate change/water dynamics in
key irrigated areas, such as northern Africa (increased irrigation
requirements; Abou-Hadid et al., 2003) and China (decreased
requirements; Tao et al., 2003a). [WGII 5.4.2.1]
At the national scale, some integrative studies exist. In the
USA, two modelling studies on adaptation of the agricultural
sector to climate change (i.e., shifts between irrigated and rainfed production) foresee a decrease in both irrigated areas and
withdrawals beyond 2030 under various climate scenarios
(Reilly et al., 2003; Thomson et al., 2005a). This is related to a
declining yield gap between irrigated and rain-fed agriculture
caused either by yield reductions of irrigated crops due to
higher temperatures, or by yield increases of rain-fed crops due
to higher precipitation. These studies did not take into account
the increasing variability of daily precipitation and, as such,
rain-fed yields are probably overestimated. [WGII 3.5.1]
Section 4
Locally, irrigated agriculture may face new problems linked to
the spatial and temporal distribution of streamflow. For instance,
at low latitudes, especially in south-east Asia, early snowmelt
may cause spring flooding and lead to a summer irrigation water
shortage. [WGII 5.8.2]
4.2.3.2 Pastures and livestock
Many of the world’s rangelands are in semi-arid areas and
susceptible to water deficits; any further decline in water
resources will greatly impact carrying capacity. As a result,
increased climate variability and droughts may lead to livestock
loss. Specifically, the impact on animal productivity due to
increased variability in weather patterns is likely to be far
greater than effects associated with changes in average climatic
conditions. The most frequent catastrophic losses arising
from a lack of prior conditioning to weather events occur in
confined cattle feedlots, with economic losses from reduced
cattle performance exceeding those associated with cattle death
losses by several-fold. [WGII 5.4.3.1]
Many of the world’s rangelands are affected by El Niño–
Southern Oscillation (ENSO) events. Under ENSO-related
drought events, in dry regions there are risks of positive
feedback between the degradation of both soils and vegetation
and reductions in rainfall, with consequences in terms of loss
of both pastoral and farming lands. [WGII 5.4.3.1] However,
while WGI TAR indicated an increased likelihood of ENSO
frequency under climate change, the WGI AR4 did not find
correlations between ENSO and climate change. [WGI TAR
SPM; WGI 10.3.5.4]
A survey of experimental data worldwide suggested that mild
warming generally increases grassland productivity, with the
strongest positive responses at high latitudes, and that the
productivity and composition of plant species in rangelands are
highly correlated with precipitation. In addition, recent findings
(see Figure 4.1) projected declines in rainfall in some major
grassland and rangeland areas (e.g., South America, southern
and northern Africa, western Asia, Australia and southern
Europe). [WGII 5.4.3.2]
For developing countries, a 14% increase in irrigation water
withdrawal by 2030 was foreseen in an FAO study that did
not consider the impacts of climate change (Bruinsma, 2003).
However, the four Millennium Ecosystem Assessment scenarios
project much smaller increases in irrigation withdrawal at the
global scale, as they assume that the area under irrigation will
only increase by between 0% and 6% by 2030; and between 0%
and 10% by 2050. [WGII 3.5.1]
Elevated atmospheric CO2 can reduce soil water depletion in
different native and semi-native temperate and Mediterranean
grassland. However, in conjunction with climate change,
increased variability in rainfall and warmer temperatures may
create more severe soil moisture limitations, and hence reduced
productivity, offsetting the beneficial effects of CO2. Other
impacts on livestock occur directly through the increase in
thermal heat load. [WGII 5.4.3.2]
The overwhelming water use increases are likely to occur in the
domestic and industrial sectors, with withdrawals increasing
by between 14% and 83% by 2050 (Millennium Ecosystem
Assessment, 2005a, b). This is based on the idea that the value
of water will be much higher for domestic and industrial uses,
which is particularly true under conditions of water stress.
[WGII 3.5.1]
4.2.3.3 Fisheries
Negative impacts of climate change on aquaculture and
freshwater fisheries include: stress due to increased temperature
and oxygen demand and decreased pH; uncertain future
water quality and volume; extreme weather events; increased
frequency of disease and toxic events; sea-level rise and
conflicts of interest with coastal defence needs; and uncertain
62
Climate change and water resources in systems and sectors
Section 4
Box 4.1: Climate change and the fisheries of the lower Mekong – an example of multiple
stresses due to human activity on a megadelta fisheries system. [WGII Box 5.3]
Fisheries are central to the lives of the people, particularly the rural poor, who live in the lower Mekong countries. Twothirds of the basin’s 60 million people are in some way active in fisheries, which represent about 10% of the GDP of
Cambodia and the Lao People’s Democratic Republic (PDR). There are approximately 1,000 species of fish commonly
found in the river, with many more marine vagrants, making it one of the most prolific and diverse faunas in the world
(MRC, 2003). Recent estimates of the annual catch from capture fisheries alone exceed 2.5 million tonnes (Hortle and
Bush, 2003), with the delta contributing over 30% of this.
Direct effects of climate change will occur due to changing patterns of precipitation, snowmelt and rising sea level, which
will affect hydrology and water quality. Indirect effects will result from changing vegetation patterns that may alter the
food chain and increase soil erosion. It is likely that human impacts on the fisheries (caused by population growth, flood
mitigation, increased water abstractions, changes in land use, and over-fishing) will be greater than the effects of climate,
but the pressures are strongly interrelated.
An analysis of the impact of climate change scenarios on the flow of the Mekong (Hoanh et al., 2004) estimated increased
maximum monthly flows of 35–41% in the basin and 16–19% in the delta (the lower value is for years 2010–2038 and
the higher value for years 2070–2099, compared with 1961–1990 levels). Minimum monthly flows were estimated to
decrease by 17–24% in the basin and 26–29% in the delta. Increased flooding would positively affect fisheries yields, but
a reduction in dry season habitat may reduce the recruitment of some species. However, planned water-management
interventions, primarily dams, are expected to have the opposite effects on hydrology, namely marginally decreasing wetseason flows and considerably increasing dry-season flows (World Bank, 2004b).
Models indicate that even a modest sea-level rise of 20 cm would cause contour lines of water levels in the Mekong
delta to shift 25 km inland during the flood season and saltwater to move further upstream (although confined within
canals) during the dry season (Wassmann et al., 2004). Inland movement of saltwater would significantly alter the species
composition of fisheries, but may not be detrimental for overall fisheries yields.
future supplies of fishmeal and oils from capture fisheries. A
case study of the multiple stresses that may affect fisheries in
developing countries is included in Box 4.1. [WGII 5.4.6.1]
Positive impacts include increased growth rates and food
conversion efficiencies; increased length of growing season;
range expansion; and the use of new areas due to decreased ice
cover. [WGII 5.4.6.1]
4.2.4
Adaptation, vulnerability and sustainable
development
Water management is a critical component that needs to adapt
in the face of both climate and socio-economic pressures in
the coming decades. Changes in water use will be driven by
the combined effects of: changes in water availability, changes
in water demand from land, as well as from other competing
sectors including urban, and changes in water management.
Practices that increase the productivity of irrigation water use
– defined as crop output per unit water use – may provide
significant adaptation potential for all land production systems
under future climate change. At the same time, improvements
in irrigation efficiency are critical to ensure the availability of
water both for food production and for competing human and
environmental needs. [WGII 3.5.1]
Several simulation studies suggest the possibility of relative
benefits of adaptation in the land sector with low to moderate
warming, although several response strategies may place
extra stress on water and other environmental resources as
warming increases. Autonomous adaptation actions are defined
as responses that will be implemented by individual farmers,
rural communities and/or farmers’ organisations, depending
on perceived or real climate change in the coming decades,
and without intervention and/or co-ordination by regional and
national governments and international agreements. To this
end, maladaptation, e.g., pressure to cultivate marginal land, or
to adopt unsustainable cultivation practices as yields drop, may
increase land degradation and endanger the biodiversity of both
wild and domestic species, possibly jeopardising future ability
to respond to increasing climate risk later in the century. Planned
adaptation, therefore, including changes in policies, institutions
and dedicated infrastructure, will be needed to facilitate and
maximise long-term benefits of adaptation responses to climate
change. [WGII 5.5]
4.2.4.1 Autonomous adaptation
Options for autonomous adaptation are largely extensions or
intensifications of existing risk management and production
enhancement activities, and are therefore already available
to farmers and communities. These include, with respect to
water:
63
Section 4
Climate change and water resources in systems and sectors
•
adoption of varieties/species with increased resistance to
heat shock and drought;
• modification of irrigation techniques, including amount,
timing or technology;
• adoption of water-efficient technologies to ‘harvest’ water,
conserve soil moisture (e.g. crop residue retention), and
reduce siltation and saltwater intrusion;
• improved water management to prevent waterlogging,
erosion and leaching;
• modification of crop calendars, i.e., timing or location of
cropping activities;
• implementation of seasonal climate forecasting.
Additional adaptation strategies may involve land-use changes
that take advantage of modified agro-climatic conditions.
[WGII 5.5.1]
A few simulation studies show the importance of irrigation water
as an adaptation technique to reduce climate change impacts. In
general, however, projections suggest that the greatest relative
benefit from adaptation is to be gained under conditions of low
to moderate warming, and that adaptation practices that involve
increased irrigation water use may in fact place additional
stress on water and environmental resources as warming and
evaporative demand increase. [WGII 5.8.1]
Many adaptation strategies in key production sectors other
than crop agriculture have also been explored, although,
without a direct focus on water issues. Adaptation strategies
that may nonetheless affect water use include, for livestock
systems, altered rotation of pastures, modification of times of
grazing, alteration of forage and animal species/breeds, altered
integration within mixed livestock/crop systems, including
the use of adapted forage crops, care to ensure adequate water
supplies, and the use of supplementary feeds and concentrates.
Pastoralist coping strategies in semi-arid and arid Kenya and
southern Ethiopia are discussed in Box 4.2. [WGII 5.4.7]
Adaptation strategies for forestry may include changes in
management intensity, species mix, rotation periods, adjusting
to altered wood size and quality, and adjusting fire management
systems. [WGII 5.5.1]
With respect to marine ecosystems, with the exception of
aquaculture and some freshwater fisheries, the exploitation
of natural fish populations precludes the kind of management
adaptations to climate change suggested for the crop, livestock
and forest sectors. Adaptation options thus centre on altering
catch size and effort. The scope for autonomous adaptation
is increasingly restricted as new regulations governing the
exploitation of fisheries and marine ecosystems come into
force. [WGII 5.5.1]
If widely adopted, adaptation strategies in production systems
have substantial potential to offset negative climate change
impacts and take advantage of positive ones. However, there
has been little evaluation of how effective and widely adopted
these adaptations may be, given the complex nature of decision
making; the diversity of responses across regions; time lags
Box 4.2: Pastoralist coping strategies in northern Kenya
and southern Ethiopia. [WGII Box 5.5]
African pastoralism has evolved in adaptation to harsh environments with very high spatial and temporal variability of
rainfall (Ellis, 1995). Several recent studies (Ndikumana et al., 2000; Hendy and Morton, 2001; Oba, 2001; McPeak
and Barrett, 2001; Morton, 2006) have focused on the coping strategies used by pastoralists during recent droughts in
northern Kenya and southern Ethiopia, and the longer-term adaptations that underlie them.
•
Mobility remains the most important pastoralist adaptation to spatial and temporal variations in rainfall, and in
drought years many communities make use of fall-back grazing areas unused in ‘normal’ dry seasons because of
distance, land tenure constraints, animal disease problems or conflict. However, encroachment on and individuation
of communal grazing lands, and the desire to settle in order to access human services and food aid, have severely
limited pastoral mobility.
•
Pastoralists engage in herd accumulation, and most evidence now suggests that this is a rational form of insurance
against drought.
•
A small proportion of pastoralists now hold some of their wealth in bank accounts, and others use informal savings
and credit mechanisms through shop-keepers.
•
Pastoralists also use supplementary feed for livestock, purchased or lopped from trees, as a coping strategy; they
intensify animal disease management through indigenous and scientific techniques; they pay for access to water
from powered boreholes.
•
Livelihood diversification away from pastoralism in this region predominantly takes the form of shifts into low-income
or environmentally unsustainable occupations such as charcoal production, rather than an adaptive strategy to
reduce ex ante vulnerability.
•
A number of intra-community mechanisms distribute both livestock products and the use of live animals to the
destitute, but these appear to be breaking down because of the high levels of covariate risk within communities.
64
Section 4
in implementation; and possible economic, institutional and
cultural barriers to change. For example, the realisable adaptive
capacity of poor subsistence farming/herding communities is
generally considered to be very low. Likewise, large areas of
forests receive minimal direct human management, limiting
adaptation opportunities. Even in more intensively managed
forests, where adaptation activities may be more feasible, long
time lags between planting and harvesting may complicate the
adoption of effective adaptation strategies. [WGII 5.1.1]
4.2.4.2 Planned adaptation
Planned adaptation solutions should focus on developing new
infrastructure, policies, and institutions that support, facilitate,
co-ordinate and maximise the benefits of new management
and land-use arrangements. This can be achieved in general
through improved governance, including addressing climate
change in development programmes; increasing investment in
irrigation infrastructure and efficient water-use technologies;
ensuring appropriate transport and storage infrastructure;
revising land tenure arrangements (including attention to welldefined property rights); and establishing accessible, efficiently
functioning markets for products and inputs (including
water pricing schemes) and for financial services (including
insurance). [WGII 5.5]
Planned adaptation and policy co-ordination across multiple
institutions may be necessary to facilitate adaptation to climate
change, in particular where falling yields create pressure to
cultivate marginal land or adopt unsustainable cultivation
practices, increasing both land degradation and the use of
resources, including water. [WGII 5.4.7]
A number of global-, national- and basin-scale adaptation
assessments show that, in general, semi-arid and arid basins
are most vulnerable with respect to water stress. If precipitation
decreases, then demand for irrigation water would make it
impossible to satisfy all other demands. Projected streamflow
changes in the Sacramento-Joaquin and Colorado River Basins
indicate that present-day water demand cannot be fulfilled by
2020, even with adaptive management practices. Increased
irrigation usage would reduce both runoff and downstream flow
(Eheart and Tornil, 1999). [WGII 3.5.1]
Policies aimed at rewarding improvements in irrigation
efficiency, either through market mechanisms or increased
regulations and improved governance, are an important tool for
enhancing adaptation capacity at a regional scale. Unintended
consequences may be increased consumptive water use
upstream, resulting in downstream users being deprived of
water that would otherwise have re-entered the stream as return
flow (Huffaker, 2005). [WGII 3.5.1]
In addition to techniques already available to farmers and
land managers today, new technical options need to be made
available through dedicated research and development efforts,
to be planned and implemented now, in order to augment
overall capacity to respond to climate change in future decades.
Technological options for enhanced R&D include traditional
Climate change and water resources in systems and sectors
breeding and biotechnology for improved resistance to climate
stresses such as drought and flooding in crop, forage, livestock,
forest and fisheries species (Box 4.3).
Box 4.3: Will biotechnology assist
agricultural and forest adaptation?
[WGII Box 5.6]
Biotechnology and conventional breeding may help
develop new cultivars with enhanced traits better suited
to adapt to climate change conditions. These include
drought and temperature stress resistance; resistance to
pests and disease, salinity and waterlogging. Additional
opportunities for new cultivars include changes in
phenology or enhanced responses to elevated CO2. With
respect to water, a number of studies have documented
genetic modifications to major crop species (e.g., maize
and soybeans) that increased their water-deficit tolerance
(as reviewed by Drennen et al., 1993; Kishor et al., 1995;
Pilon-Smits et al., 1995; Cheikh et al., 2000), although
this may not extend to the wider range of crop plants.
In general, too little is currently known about how the
desired traits achieved by genetic modification perform
in real farming and forestry applications (Sinclair and
Purcell, 2005).
4.2.4.3 Food security and vulnerability
All four dimensions of food security: namely, food availability
(production and trade), access to food, stability of food
supplies, and food utilisation (the actual processes involved
in the preparation and consumption of food), are likely to be
affected by climate change. Importantly, food security will
depend not only on climate and socio-economic impacts on
food production, but also (and critically so) on changes to trade
flows, stocks, and food aid policy. In particular, climate change
will result in mixed and geographically varying impacts on
food production and, thus, access to food. Tropical developing
countries, many of which have poor land and water resources
and already face serious food insecurity, may be particularly
vulnerable to climate change. [WGII 5.6.5]
Changes in the frequency and intensity of droughts and flooding
will affect the stability of, and access to, critical food supplies.
Rainfall deficits can dramatically reduce both crop yields and
livestock numbers in the semi-arid tropics. Food insecurity and
loss of livelihood would be further exacerbated by the loss of
both cultivated land and coastal fish nurseries as a result of
inundation and coastal erosion in low-lying areas. [WGII 5.6.5]
Climate change may also affect food utilisation through impacts
on environmental resources, with important additional health
consequences. [WGII Chapter 8] For example, decreased water
availability in already water-scarce regions, particularly in the subtropics, has direct negative implications for both food processing
and consumption. Conversely, the increased risk of flooding of
human settlements in coastal areas from both rising sea levels and
65
Climate change and water resources in systems and sectors
increased heavy precipitation may increase food contamination and
disease, reducing consumption patterns. [WGII 5.6.5]
4.2.4.4 Water quality issues
In developing countries, the microbiological quality of water
is poor because of the lack of sanitation, lack of proper
treatment methods, and poor health conditions (Lipp et al.,
2001; Jiménez, 2003; Maya et al., 2003; WHO, 2004). Climate
change may impose additional stresses on water quality,
especially in developing countries (Magadza, 2000; Kashyap,
2004; Pachauri, 2004). As yet there are no studies focusing on
micro-organism life cycles relevant to developing countries
under climate change, including a much-needed focus on the
effects of poorly treated wastewater use for irrigation and its
links to endemic outbreaks of helminthiasis (WHO/UNICEF,
2000). [WGII 3.4.4]
About 10% of the world’s population consumes crops irrigated
with untreated or poorly treated wastewater, mostly in
developing countries in Africa, Asia and Latin America. This
number is projected to grow with population and food demand.
[WGII 8.2.5] Increased use of properly treated wastewater for
irrigation is therefore a strategy to combat both water scarcity
and some related health problems. [WGII 3.4.4]
4.2.4.5 Rural communities, sustainable development and
water conflicts
Transboundary water co-operation is recognised as an effective
policy and management tool to improve water management
across large regions sharing common resources. Climate change
and increased water demand in future decades will represent an
added challenge to such framework agreements, increasing the
potential for conflict at the local level. For instance, unilateral
measures for adapting to climate-change-related water
shortages can lead to increased competition for water resources.
Furthermore, shifts in land productivity may lead to a range
of new or modified agricultural systems, necessary to maintain
production, including intensification practices. The latter, in
turn, can lead to additional environmental pressures, resulting
in loss of habitat and reduced biodiversity, siltation, soil erosion
and soil degradation. [WGII 5.7]
Impacts on trade, economic, and environmental development and
land use may also be expected from measures implemented to
substitute fossil fuels through biofuels, such as by the European
Biomass Action Plan. Large-scale biofuel production raises
questions on several issues including fertiliser and pesticide
requirements, nutrient cycling, energy balance, biodiversity
impacts, hydrology and erosion, conflicts with food production,
and the level of financial subsidies required. In fact, the emerging
challenges of future decades include finding balance in the
competition for land and raw materials for the food, forestry
and energy sectors, e.g., devising solutions that ensure food and
local rural development rights while maximising energy and
climate mitigation needs. [LULUCF 4.5.1]
In North America, drought may increase in continental interiors
and production areas may shift northwards (Mills, 1994),
66
Section 4
especially for maize and soybean production (Brklacich et al.,
1997). [WGII TAR 15.2.3.1] In Mexico, production losses may
be dominated by droughts, as agro-ecological zones suitable for
maize cultivation decrease (Conde et al., 1997). [WGII TAR
14.2.2.1] Drought is an important issue throughout Australia
for social, political, geographical and environmental reasons. A
change in climate towards drier conditions as a result of lower
rainfall and higher evaporative demand would trigger more
frequent or longer drought declarations under current Australian
drought policy schemes. [WGII TAR 12.5.6]
Water resources are a key vulnerability in Africa for household,
agricultural and industrial uses. In shared river basins, regional
co-operation protocols are needed to minimise both adverse
impacts and the potential for conflicts. For instance, the surface
area of Lake Chad varies from 20,000 km2 during the dry
season to 50,000 km2 during the wet season. While precise
boundaries have been established between Chad, Nigeria,
Cameroon and Niger, sectors of these boundaries that are
located in the rivers that drain into Lake Chad have never been
determined, and additional complications arise as a result of
both flooding and water recession. Similar problems on the
Kovango River between Botswana and Namibia led to military
confrontation. [WGII TAR 10.2.1.2]
Growing water scarcity, increasing population, degradation
of shared freshwater ecosystems and competing demands for
shrinking natural resources distributed over such a huge area
involving so many countries have the potential for creating
bilateral and multilateral conflicts. In semi-arid Africa,
pastoralism is the main economic activity, with pastoral
communities including transnational migrants in search of
new seasonal grazing. In drought situations, such pastoralists
may come into conflict with settled agrarian systems.
[WGII TAR 10.2.1.2]
Asia dominates world aquaculture, with China alone producing
about 70% of all farmed fish, shrimp and shellfish (FAO, 2006).
Fish, an important source of food protein, is critical to food
security in many countries of Asia, particularly among poor
communities in coastal areas. Fish farming requires land and
water, two resources that are already in short supply in many
countries in Asia. Water diversion for shrimp ponds has lowered
groundwater levels noticeably in coastal areas of Thailand.
[WGII TAR 11.2.4.4]
At least 14 major international river watersheds exist in Asia.
Watershed management is challenging in countries with high
population density, which are often responsible for the use of
even the most fragile and unsuitable areas in the watersheds
for cultivation, residential, and other intensive activities. As a
result, in many countries, in particular Bangladesh, Nepal, the
Philippines, Indonesia and Vietnam, many watersheds suffer
badly from deforestation, indiscriminate land conversion,
excessive soil erosion and declining land productivity. In the
Climate change and water resources in systems and sectors
Section 4
absence of appropriate adaptation strategies, these watersheds
are highly vulnerable to climate change. [WGII TAR 11.2.3.2]
4.2.4.6 Mitigation
Adaptation responses and mitigation actions may occur
simultaneously in the agricultural and forestry sector; their
efficacy will depend on the patterns of realised climate change
in the coming decades. The associated interactions between
these factors (climate change, adaptation and mitigation) will
frequently involve water resources. [WGIII 8.5, Table 8.9]
Adaptation and mitigation strategies may either exhibit
synergies, where both actions reinforce each other, or be
mutually counter-productive. With respect to water, examples
of adaptation strategies that reduce mitigation options largely
involve irrigation, in relation to the energy costs of delivering
water and the additional greenhouse gas emissions that may
be associated with modified cultivation practices. Using
renewables for water extraction and delivery could, however,
eliminate such conflict. Likewise, some mitigation strategies
may have negative adaptation consequences, such as increasing
dependence on energy crops, which may compete for water
resources, reduce biodiversity, and thus increase vulnerability
to climatic extremes. [WGIII 12.1.4, 12.1.4]
On the other hand, many carbon-sequestration practices
involving reduced tillage, increased crop cover and use of
improved rotation systems, in essence constitute – and were
in fact originally developed as – ‘good-practice’ agro-forestry,
leading to production systems that are more resilient to climate
variability, thus providing good adaptation in the face of
increased pressure on water and soil resources (Rosenzweig
and Tubiello, 2007). [WGII 5.4.2; WGIII 8.5]
4.3 Human health
to climate change. Populations with high rates of disease and
disability cope less successfully with stresses of all kinds,
including those related to climate change. [WGII 8.1.1]
The World Health Organization (WHO) and UNICEF Joint
Monitoring Programme currently estimates that 1.1 billion
people (17% of the global population) lack access to water
resources, where access is defined as the availability of at least
20 litres of water per person per day from an improved water
source within a distance of 1 km. An improved water source is
one that provides ‘safe’ water, such as a household connection
or a bore hole. Nearly two-thirds of the people without access
are in Asia. In sub-Saharan Africa, 42% of the population is
without access to improved water. The WHO estimates that
the total burden of disease due to inadequate water supply,
and poor sanitation and hygiene, is 1.7 million deaths per year.
Health outcomes related to water supply and sanitation are a
focal point of concern for climate change in many countries.
In vulnerable regions, the concentration of risks from both
food and water insecurity can make the impact of any weather
extreme (for example, flood and drought) particularly severe
for the households affected. [WGII 9.2.2]
Changes in climate extremes have the potential to cause severe
impacts on human health. Flooding is expected to become more
severe with climate change, and this will have implications for
human health. Vulnerability to flooding is reduced when the
infrastructure is in place to remove solid waste, manage waste
water, and supply potable water. [WGII 8.2.2]
Lack of water for hygiene is currently responsible for a significant
burden of disease worldwide. A small and unquantified
proportion of this burden can be attributed to climate variability
or climate extremes. ‘Water scarcity’ is associated with multiple
adverse health outcomes, including diseases associated with
water contaminated with faecal and other hazardous substances
(e.g., parasites).
Human health, incorporating physical, social and psychological
well-being, depends on an adequate supply of potable water
and a safe environment. Human beings are exposed to climate
change directly through weather patterns (more intense and
frequent extreme events), and indirectly through changes in
water, air, food quality and quantity, ecosystems, agriculture,
livelihoods and infrastructure. [WGII 8.1.1] Due to the very
large number of people that may be affected, malnutrition and
water scarcity may be the most important health consequences
of climate change (see Sections 4.2 and 4.4). [WGII 8.4.2.3]
Childhood mortality and morbidity due to diarrhoea in lowincome countries, especially in sub-Saharan Africa, remains
high despite improvements in care and the use of oral
rehydration therapy. Climate change is expected to increase
water scarcity, but it is difficult to assess what this means at the
household level for the availability of water, and therefore for
health and hygiene. There is a lack of information linking largescale modelling of climate change to small-scale impacts at the
population or household level. Furthermore, any assessments of
future health impacts via changes in water availability need to
take into account future improvements in access to ‘safe’ water.
[WGII 8.2.5, 8.4.2.2]
Population health has improved remarkably over the last
50 years, but substantial inequalities in health persist within
and between countries. The Millennium Development Goal
(MDG) of reducing the mortality rate in children aged under
5 years old by two-thirds by 2015 is unlikely to be reached in
some developing countries. Poor health increases vulnerability
and reduces the capacity of individuals and groups to adapt
4.3.1.1 Implications for drinking-water quality
The relationship between rainfall, river flow and contamination
of the water supply is highly complex, as discussed below both
for piped water supplies and for direct contact with surface
waters. If river flows are reduced as a consequence of less
rainfall, then their ability to dilute effluent is also reduced
– leading to increased pathogen or chemical loading. This
4.3.1
Context
67
Climate change and water resources in systems and sectors
could represent an increase in human exposures or, in places
with piped water supplies, an increased challenge to water
treatment plants. During the dry summer of 2003, low flows in
the Netherlands resulted in apparent changes in water quality
(Senhorst and Zwolsman, 2005). The marked seasonality of
cholera outbreaks in the Amazon was associated with low river
flow in the dry season (Gerolomo and Penna, 1999), probably
due to high pathogen concentrations in pools. [WGII 8.2.5]
Drainage and storm water management is important in lowincome urban communities, as blocked drains can cause
flooding and increased transmission of vector-borne diseases
(Parkinson and Butler, 2005). Cities with combined sewer
overflows can experience increased sewage contamination
during flood events. [WGII 8.2.5]
In high-income countries, rainfall and runoff events may
increase the total microbial load in watercourses and drinkingwater reservoirs, although the linkage to cases of human disease
is less certain because the concentration of contaminants is
diluted. The seasonal contamination of surface water in early
spring in North America and Europe may explain some of the
seasonality in sporadic cases of water-borne diseases such
as cryptosporidiosis and campylobacteriosis. A significant
proportion of notified water-borne disease outbreaks are
related to heavy precipitation events, often in conjunction with
treatment failures. [WGII 14.2.5, 8.2.5]
Freshwater harmful algal blooms (HABs) produce toxins that
can cause human diseases. The occurrence of such blooms in
surface waters (rives and lakes) may increase due to higher
temperatures. However, the threat to human health is very low,
as direct contact with blooms is generally restricted. There
is a low risk of contamination of water supplies with algal
toxins but the implications for human health are uncertain.
[WGII 8.2.4, 3.4.4]
In areas with poor water supply infrastructure, the transmission
of enteric pathogens peaks during the rainy season. In addition,
higher temperatures were found to be associated with increased
episodes of diarrhoeal disease (Checkley et al., 2000; Singh et
al., 2001; Vasilev, 2003; Lama et al., 2004). The underlying
incidence of these diseases is associated with poor hygiene and
lack of access to safe water. [WGII 8.2.5]
4.3.1.2
Disasters, including wind storms and floods
The previous sections have described how climate change will
affect the risk of water-related disasters, including glacial lake
outburst floods (GLOFs), increased storm surge intensity, and
changes in flood risk (see Section 3.2) including flash flooding
and urban flooding, with some reductions in risk of spring
snowmelt floods. [WGII 3.4.3] Floods have a considerable
impact on health both in terms of number of deaths and disease
burden, and also in terms of damage to the health infrastructure.
[WGII 8.2.2] While the risk of infectious disease following
68
Section 4
flooding is generally low in high-income countries, populations
with poor infrastructure and high burdens of infectious disease
often experience increased rates of diarrhoeal diseases after
flood events. There is increasing evidence of the impact that
climate-related disasters have on mental health, with people
who have suffered the effects of floods experiencing long-term
anxiety and depression. [WGII 8.2.2, 16.4.5]
Flooding and heavy rainfall may lead to contamination
of water with chemicals, heavy metals or other hazardous
substances, either from storage or from chemicals already in
the environment (e.g., pesticides). Increases in both population
density and industrial development in areas subject to natural
disasters increase both the probability of future disasters and
the potential for mass human exposure to hazardous materials
during these events. [WGII 8.2.2]
4.3.1.3 Drought and infectious disease
For a few infectious diseases, there is an established rainfall
association that is not related to the consumption of drinkingwater (quality or quantity) or arthropod vectors. The spatial
distribution, intensity and seasonality of meningococcal
(epidemic) meningitis in the Sahelian region of Africa is
related to climatic and environmental factors, particularly
drought, although the causal mechanism is not well understood.
The geographical distribution of meningitis has expanded
in West Africa in recent years, which may be attributable to
environmental change driven both by land-use changes and by
regional climate change. [WGII 8.2.3.1]
4.3.1.4 Dust storms
Windblown dust originating in desert regions of Africa, the
Arabian Peninsula, Mongolia, central Asia and China can
affect air quality and population health in distant areas. When
compared with non-dust weather conditions, dust can carry
large concentrations of respirable particles; trace elements
that can affect human health; fungal spores; and bacteria.
[WGII 8.2.6.4]
4.3.1.5 Vector-borne diseases
Climate influences the spatial distribution, intensity of
transmission, and seasonality of diseases transmitted by
vectors (e.g., malaria) and diseases that have water snails as an
intermediate host (e.g., schistosomiasis). [WGII 8.2.8] During
droughts, mosquito activity is reduced but, if transmission
drops significantly, the population of non-immune individuals
may increase. In the long term, the incidence of mosquito-borne
diseases such as malaria decreases because mosquito abundance
is reduced, although epidemics may still occur when suitable
climate conditions occur. [WGII 8.2.3.1]
The distribution of schistosomiasis, a water-related parasitic
disease with aquatic snails as intermediate hosts, is influenced
by climate factors in some locations, For example, the
observed change in the distribution of schistosomiasis in China
Climate change and water resources in systems and sectors
Section 4
over the past decade may in part reflect the recent warming
trend. Irrigation schemes have also been shown to increase
the incidence of schistosomiasis, when appropriate control
measures are not implemented. [WGII 8.2.8.3]
4.3.2
Observations
There is a wide range of driving forces that can affect and
modify the impact of climate change on human health outcomes.
Because of the complexity of the association between climate
factors and disease, it is often not possible to attribute changes
in specific disease patterns to observed climate changes.
Furthermore, health data series of sufficient quality and length
are rarely available for such studies. There are no published
studies of water-related impacts on health that describe patterns
of disease that are robustly attributed to observed climate change.
However, there are several reports of adaptive responses in the
water sector designed to reduce the impacts of climate change.
[WGII Chapter 7]
Observed trends in water-related disasters (floods, wind
storms) and the role of climate change are discussed elsewhere.
[WGII 1.3]
4.3.3
Projections
Climate change is expected to have a range of adverse effects
on populations where the water and sanitation infrastructure is
inadequate to meet local needs. Access to safe water remains an
extremely important global health issue. More than two billion
people live in the dry regions of the world, and these people
suffer more than others from malnutrition, infant mortality
and diseases related to contaminated or insufficient water.
Water scarcity constitutes a serious constraint to sustainable
development (Rockstrom, 2003). [WGII 8.2.5, 8.4.2.2]
4.3.4
Adaptation, vulnerability and sustainable
development
Weak public health systems and limited access to primary health
care contribute both to high levels of vulnerability and to low
adaptive capacity for hundreds of millions of people. [WGII
8.6] Fundamental constraints exist in low-income countries,
where population health will depend upon improvements in
the health, water, agriculture, transport, energy and housing
sectors. Poverty and weak governance are the most serious
obstacles to effective adaptation. Despite economic growth,
low-income countries are likely to remain vulnerable over the
medium term, with fewer options than high-income countries
for adapting to climate change. Therefore, if adaptation
strategies are to be effective, they should be designed in the
context of the development, environment and health policies in
place in the target area. Many options that can be used to reduce
future vulnerability are of value in adapting to current climate,
and can also be used to achieve other environmental and social
objectives. [WGII 8.6.3]
The potential adverse health effects of any adaptation strategy
should be evaluated before that strategy is implemented.
For example, a micro-dam and irrigation programmes have
been shown to increase local malaria mortality. [WGII 8.6.4]
Measures to combat water scarcity, such as the reuse of
untreated or partially treated wastewater for irrigation, also
have implications for human health. Irrigation is currently an
important determinant of the spread of infectious diseases such
as malaria and schistosomiasis (Sutherst, 2004). Strict waterquality guidelines for wastewater irrigation are designed to
prevent health risks from pathogenic organisms, and to guarantee
crop quality (Steenvoorden and Endreny, 2004). Some diseases,
such as helminthiasis, are transmitted by consuming crops
irrigated with polluted water or wastewater and, in the rural
and peri-urban areas of most low-income countries, the use of
sewage and wastewater for irrigation, a common practice, is a
source of faecal–oral disease transmission. At present, at least
one-tenth of the world’s population consumes crops irrigated
with wastewater. However, increasing water scarcity and food
demand, coupled with poor sanitation, will facilitate the use of
low-quality water. If such problems are to be controlled, then
programmes of wastewater treatment and planned wastewater
reuse need to be developed. [WGII 8.6.4, 3.4.4]
4.4 Water supply and sanitation
The observed effects of climate change on water resource
quantity and quality have been discussed in detail in Sections 4.2
and 4.3. This section summarises the main points and describes
their implications for water supply and sanitation services.
4.4.1
Context
Statistics on present-day access to safe water have already been
provided in Section 4.3.1. Access to safe water is now regarded
as a universal human right. However, the world is facing
increasing problems in providing water services, particularly in
developing countries. There are several reasons for this, which
are not necessarily linked to climate change. A lack of available
water, a higher and more uneven water demand resulting
from population growth in concentrated areas, an increase in
urbanisation, more intense use of water to improve general
well-being, and the challenge to improve water governance, are
variables that already pose a tremendous challenge to providing
satisfactory water services. In this context, climate change
simply represents an additional burden for water utilities, or
any other organisation providing water services, in meeting
customers’ needs. It is difficult to identify climate change
effects at a local level, but the observed effects combined with
projections provide a useful basis to prepare for the future.
4.4.2
Observations
Table 4.1 summarises possible linkages between climate change
and water services.
69
Section 4
Climate change and water resources in systems and sectors
Table 4.1: Observed effects of climate change and its observed/possible impacts on water services. [WGII Chapter 3]
Observed effect
Observed/possible impacts
Increase in atmospheric
temperature
• Reduction in water availability in basins fed by glaciers that are shrinking, as observed in some cities along the
Andes in South America (Ames, 1998; Kaser and Osmaston, 2002)
Increase in surface water
temperature
• Reductions in dissolved oxygen content, mixing patterns, and self purification capacity
• Increase in algal blooms
Sea-level rise
• Salinisation of coastal aquifers
Shifts in precipitation
patterns
• Changes in water availability due to changes in precipitation and other related phenomena (e.g., groundwater
recharge, evapotranspiration)
Increase in interannual
precipitation variability
• Increases the difficulty of flood control and reservoir utilisation during the flooding season
Increased
evapotranspiration
• Water availability reduction
• Salinisation of water resources
• Lower groundwater levels
More frequent and
intense extreme events
• Floods affect water quality and water infrastructure integrity, and increase fluvial erosion, which introduces
different kinds of pollutants to water resources
• Droughts affect water availability and water quality
4.4.3
Projections
Reduced water availability may result from:
a. decreased flows in basins fed by shrinking glaciers and
longer and more frequent dry seasons,
b. decreased summer precipitation leading to a reduction
of stored water in reservoirs fed with seasonal rivers (du
Plessis et al., 2003),
c. interannual precipitation variability and seasonal shifts in
streamflow,
d. reductions in inland groundwater levels,
e. the increase in evapotranspiration as a result of higher
air temperatures, lengthening of the growing season and
increased irrigation water usage,
f. salinisation (Chen et al., 2004).
According to projections, the number of people at risk from
increasing water stress will be between 0.4 billion and 1.7 billion
by the 2020s, between 1.0 billion and 2.0 billion by the 2050s
and between 1.1 billion and 3.2 billion by the 2080s (Arnell,
2004), the range being due to the different SRES scenarios
considered. [WGII 3.2, 3.5.1]
In some areas, low water availability will lead to groundwater
over-exploitation and, with it, increasing costs of supplying water
for any use as a result of the need to pump water from deeper
and further away. Additionally, groundwater over-exploitation
may lead in some cases to water quality deterioration. For some
regions of India, Bangladesh, China, north Africa, Mexico and
Argentina, there are more than 100 million people suffering
from arsenic poisoning and fluorosis (a disease of the teeth
70
or bones caused by excessive consumption of fluoride
in drinking water) (UN, 2003); this can result in an even
worse situation if people are forced to use more water from
groundwater as a result of the lack of reliable surface water
sources. [WGII 3.4.4]
Increasing water scarcity combined with increased food demand
and/or water use for irrigation as a result of higher temperatures
are likely to lead to enhanced water reuse. Areas with low
sanitation coverage might be found to be practising (as a new
activity or to a greater degree) uncontrolled water reuse (reuse
that is performed using polluted water or even wastewater).
[WGII 3.3.2, 8.6.4]
Water quality deterioration as result of flow variation. Where a
reduction in water resources is expected, a higher water pollutant
concentration will result from a lower dilution capacity. [WGII
3.4.4, 14.4.1] At the same time, increased water flows will
displace and transport diverse compounds from the soil to water
resources through fluvial erosion. [WGII 3.4]
Similarly, an increase in morbidity and mortality rates from
water-borne diseases for both more humid and drier scenarios
is expected, owing to an insufficient supply of potable water
(Kovats et al., 2005; Ebi et al., 2006), and the greater presence
of pathogens conveyed by high water flows during extreme
precipitation. Increased precipitation may also result in higher
turbidity and nutrient loadings in water. The water utility of
New York City has identified heavy precipitation events as
one of its major climate-change-related concerns because they
Section 4
can raise turbidity levels in some of the city’s main reservoirs
by up to 100 times the legal limit for source quality at the
utility’s intakes, requiring substantial additional treatment and
monitoring costs (Miller and Yates, 2006). [WGII 3.5.1]
Increased runoff. In some regions, more water will be available
which, considering the present global water situation, will
be generally beneficial. Nevertheless, provisions need to be
made to use this to the world’s advantage. For example, while
increased runoff in eastern and southern Asia is expected as a
result of climate change, water shortages in these areas may not
be addressed, given a lack of resources for investing in the new
storage capacity required to capture the additional water and to
enable its use during the dry season. [WGII 3.5.1]
Higher precipitation in cities may affect the performance
of sewer systems; uncontrolled surcharges may introduce
microbial and chemical pollutants to water resources that are
difficult to handle through the use of conventional drinkingwater treatment processes. Several studies have shown that the
transmission of enteric pathogens resistant to chlorination, such
as Cryptosporidium, is high during the rainy season (Nchito
et al., 1998; Kang et al., 2001). This is a situation that could
be magnified in developing countries, where health levels
are lower and the pathogen content in wastewater is higher
(Jiménez, 2003). In addition, extreme precipitation leading to
floods puts water infrastructure at risk. During floods, water and
wastewater treatment facilities are often out of service, leaving
the population with no sanitary protection. [WGII 3.2, 3.4.4,
8.2.5]
Water quality impairment as result of higher temperatures.
Warmer temperatures, combined with higher phosphorus
concentrations in lakes and reservoirs, promote algal blooms
that impair water quality through undesirable colour, odour and
taste, and possible toxicity to humans, livestock and wildlife.
Dealing with such polluted water has a high cost with the
available technology, even for water utilities from developed
countries (Environment Canada, 2001). Higher water
temperatures will also enhance the transfer of volatile and semivolatile pollutants (ammonia, mercury, PCBs (polychlorinated
biphenyls), dioxins, pesticides) from water and wastewater to
the atmosphere. [WGII 3.4.4]
Increased salinisation. The salinisation of water supplies from
coastal aquifers due to sea-level rise is an important issue, as
around one-quarter of the world’s population live in coastal
regions that are generally water-scarce and undergoing rapid
population growth (Small and Nicholls, 2003; Millennium
Ecosystem Assessment, 2005b). Salinisation can also affect
inland aquifers due to a reduction in groundwater recharge
(Chen et al., 2004). [WGII 3.2, 3.4.2]
The populations that will be most affected by climate change
with respect to water services are those located in the already
water-stressed basins of Africa, the Mediterranean region, the
Near East, southern Asia, northern China, Australia, the USA,
central and northern Mexico, north-eastern Brazil and the
Climate change and water resources in systems and sectors
west coast of South America. Those particularly at risk will be
populations living in megacities, rural areas strongly dependent
on groundwater, small islands, and in glacier- or snowmeltfed basins (more than one-sixth of the world’s population
live in snowmelt basins). Problems will be more critical in
economically depressed areas, where water stress will be
enhanced by socio-economic factors (Alcamo and Henrichs,
2002; Ragab and Prudhomme, 2002). [WGII 3.3.2, 3.5.1]
4.4.4
Adaptation, vulnerability and sustainable
development
Given the problems envisaged above, it is important for water
utilities located in regions at risk to plan accordingly. Most
water supply systems are well able to cope with the relatively
small changes in mean temperature and precipitation that are
projected to occur in the decades ahead, except at the margin
where a change in the mean requires a change in the system
design or the technology used; e.g., where reduced precipitation
makes additional reservoirs necessary (Harman et al., 2005),
or leads to saline intrusion into the lower reaches of a river, or
requires new water treatment systems to remove salts. A recent
example of adaptation is in southern Africa (Ruosteenoja et
al. 2003), where the city of Beira in Mozambique is already
extending its 50 km pumping main a further 5 km inland to be
certain of fresh water. [WGII 7.4.2.3.1]
Water services are usually provided using engineered systems.
These systems are designed using safety factors and have a life
expectancy of 20–50 years (for storage reservoirs it can be even
longer). Reviews of the resilience of water supplies and the
performance of water infrastructure have typically been done by
using observed conditions alone. The use of climate projections
should also be considered, especially in cases involving systems
that deal with floods and droughts.
Decrease in water availability. Except for a few industrialised
countries, water use is increasing around the world due to
population and economic growth, lifestyle changes and
expanded water supply systems. [WGII 3.3] It is important to
implement efficient water-use programmes in regions where
water availability is likely to decrease, as large investments
might be required to ensure adequate supplies, either by
building new storage reservoirs or by using alternative water
sources. Reductions in water use can delay, or even eliminate,
the need for additional infrastructure. One of the quickest ways
to increase water availability is through minimising water losses
in urban networks and in irrigation systems. Other alternatives
for reducing the need for new water supplies include rainwater
harvesting as well as controlled reuse. [WGII 3.5, 3.6]
Lower water quality caused by flow variations. The protection
of water resources is an important, cost-effective strategy for
facing future problems concerning water quality. While this
is a common practice for some countries, new and innovative
approaches to water quality management are required around
the world. One such approach is the implementation of water
safety plans (WSP) to perform a comprehensive assessment
71
Climate change and water resources in systems and sectors
Section 4
and management of risks from the catchment to consumer, as
proposed by the WHO (2005). Also, the design and operation
of water and wastewater treatment plants should be reviewed
periodically, particularly in vulnerable areas, to ensure or
increase their reliability and their ability to cope with uncertain
flow variations.
distribution of gains and losses across different sectors of
society. Institutional settings need to find better ways to allocate
water, using principles – such as equity and efficiency – that
may be politically difficult to implement in practice. These
settings also need to consider the management of international
basins and surface and groundwater basins. [WGII 3.5.1]
Desalinisation. Water treatment methods are an option for
dealing with increasing salt content in places at risk, such as
highly urbanised coastal areas relying on aquifers sensitive to
saline intrusion. At present, available technologies are based
mostly on membranes and are more costly than conventional
methods for the treatment of freshwater supplies. The
desalination cost for seawater is estimated at around US$1/m3,
for brackish water it is US$0.60/m3 (Zhou and Tol, 2005), and
freshwater chlorination costs US$0.02/m3. Fortunately the cost
of desalinisation has been falling, although it still has a high
energy demand. Desalinisation costs need to be compared with
the costs of extending pipelines and eventually relocating water
treatment works in order to have access to freshwater. As a rough
working rule, the cost of construction of the abstraction and
treatment works and the pumping main for an urban settlement’s
water supply is about half the cost of the entire system. [WGII
7.5] However, in the densely populated coastal areas of Egypt,
China, Bangladesh, India and south-east Asia, desalination
costs may still be prohibitive. [WGII 3.5.1] If the use of
desalination increases in the future, environmental side-effects
such as impingement on and entrainment of marine organisms
by seawater desalination plants, and the safe disposal of highly
concentrated brines that can also contain other chemicals, will
need to be addressed. [WGII 3.3.2]
To confront the additional stress induced by climate change,
public participation in water planning will be necessary,
particularly in regard to changing views on the value of water,
the importance and role that water reuse will play in the future,
and the contribution that society is willing to make to the
mitigation of water-related impacts.
More and different approaches for coping with wastewater. For
sewers and wastewater treatment plants, strategies for coping
with higher and more variable flows will be needed. These
should include new approaches such as the use of decentralised
systems, the construction of separate sewers, the treatment of
combined sewer overflows (i.e., the mixture of wastewater
and runoff in cities), and injecting rainwater into the subsoil.
Given the high cost involved in increasing the capacity of
urban wastewater treatment plants, appropriately financed
schemes should be put in place to consider local conditions. For
rural areas, sanitation coverage is generally too low, and local
action plans need to be formulated using low-cost technologies,
depending on the locality and involving the community. [WGII
7.4.2.3]
Better administration of water resources. As well as considering
the adaptation measures already discussed, integrated water
management, including climate change as an additional
variable, should be considered as an efficient tool. Reduced,
increased or a greater variability in water availability will
lead to conflicts between water users (agriculture, industries,
ecosystems and settlements). The institutions governing water
allocation will play a major role in determining the overall
social impact of a change in water availability, as well as the
72
To implement policy based on the principles of integrated
water management, better co-ordination between different
governmental entities should be sought, and institutional
and legal frameworks should be reviewed to facilitate the
implementation of adaptation measures. Climate change will
be felt by all stakeholders involved in the water management
process, including users. Therefore, all should be aware of its
possible impacts on the system in order to take appropriate
decisions and be prepared to pay the costs involved. In the case
of wastewater disposal norms, for example, the overall strategy
used will possibly need to be reviewed, as long as it is based
on the self-purification capacity of surface water, which will be
reduced by higher temperatures. [WGII 3.4.4]
Developed countries. In developed countries, drinking-water
receives extensive treatment before it is supplied to the consumer
and the wastewater treatment level is high. Such benefits, as
well as proper water source protection, need to be maintained
under future climatic change, even if additional cost is to be
incurred, for instance by including additional water treatment
requirements. For small communities or rural areas, measures
to be considered may include water source protection as a better
cost–benefit option.
Developing countries. Unfortunately, some countries may not
have sufficient economic resources to face the challenges posed
by climate change. Poor countries already need additional
resources to overcome problems with inadequate infrastructure,
and thus they will be more vulnerable to projected impacts
on water quantity and quality, unless low-cost options and
affordable finance options are available.
Because several of the already identified adaptation and
mitigation options are simply not viable, it is expected that
developing countries may have to adapt by using unsustainable
practices such as increasing groundwater over-exploitation
or reusing a greater amount of untreated wastewater. These
‘solutions’ are attractive because they can easily be implemented
at an individual, personal, level. Therefore, low-cost and safe
options which do not necessarily imply conventional solutions
need to be developed, particularly to provide water services for
poor communities that do not even have formal water utilities in
Section 4
Climate change and water resources in systems and sectors
many instances. Unfortunately, there are few studies available
on this issue. [WGII 3.4.3, 8.6.4]
designed for the climate conditions projected to prevail in the
future. [WGII 3.4.3, 3.5, 7.4.2.3]
In summary, climate change can have positive and negative
impacts on water services. It is important, therefore, to
be aware of its consequences at a local level and to plan
accordingly. At the present time, only some water utilities in
a few countries, including the Netherlands, the UK, Canada
and the USA, have begun to consider the implications of
climate change in the context of flood control and water
supply management. [WGII 3.6]
4.5.1
4.5 Settlements and infrastructure
Changes in water availability, water quality, precipitation
characteristics, and the likelihood and magnitude of flooding
events are expected to play a major role in driving the impacts
of climate change on human settlements and infrastructure
(Shepherd et al., 2002; Klein et al., 2003; London Climate
Change Partnership, 2004; Sherbinin et al., 2006). These impacts
will vary regionally. In addition, impacts will depend greatly on
the geophysical setting, level of socio-economic development,
water allocation institutions, nature of the local economic
base, infrastructure characteristics and other stressors. These
include pollution, ecosystem degradation, land subsidence
(due either to loss of permafrost, natural isostatic processes,
or human activities such as groundwater use) and population
growth (UNWWAP, 2003, 2006; Faruqui et al., 2001; UNDP,
2006). Globally, locations most at risk of freshwater supply
problems due to climate change are small islands, arid and
semi-arid developing countries, regions whose freshwater is
supplied by rivers fed by glacial melt or seasonal snowmelt,
and countries with a high proportion of coastal lowlands and
coastal megacities, particularly in the Asia–Pacific region
(Alcamo and Henrichs, 2002; Ragab and Prudhomme, 2002).
[WGII 6.4.2, 20.3]
Growing population density in high-risk locations, such as
coastal and riverine areas, is very likely to increase vulnerability
to the water-related impacts of climate change, including flood
and storm damages and water quality degradation as a result
of saline intrusion. [WGII 6.4.2, 7.4.2.4] Settlements whose
economies are closely linked to a climate-sensitive waterdependent activity, such as irrigated agriculture, water-related
tourism and snow skiing, are likely to be especially vulnerable
to the water resource impacts of climate change (Elsasser and
Burki, 2002; Hayhoe et al., 2004). [WGII 7.4.3, 12.4.9]
Infrastructure associated with settlements includes buildings,
transportation networks, coastal facilities, water supply and
wastewater infrastructure, and energy facilities. Infrastructure
impacts include both direct damages, for example as a result
of flood events or structural instabilities caused by rainfall
erosion or changes in the water table, as well as impacts on
the performance, cost and adequacy of facilities that were not
Settlements
Many human settlements currently lack access to adequate,
safe water supplies. The World Health Organization estimates
that 1.1 billion people worldwide do not have access to safe
drinking water, and 2.4 billion are without access to adequate
sanitation (WHO/UNICEF, 2000). Poor urban households
frequently do not have networked water supply access, and
thus are especially vulnerable to rising costs for drinking water
(UN-HABITAT, 2003; UNCHS, 2003, 2006; UNDP, 2006).
For example, in Jakarta, some households without regular
water service reportedly spend up to 25% of their income
on water and, during the hot summer of 1998 in Amman,
Jordan, refugee-camp residents who were not connected to the
municipal water system paid much higher rates for water than
other households (Faruqui et al., 2001). The impacts of climate
change on water availability and source water quality are very
likely to make it increasingly difficult to address these problems,
especially in areas where water stress is projected to increase
due to declining runoff coupled with increasing population.
[WGII 3.5.1] Rapidly growing settlements in semi-arid areas of
developing countries, particularly poor communities that have
limited adaptive capacity, are especially vulnerable to declines
in water availability and associated increases in the costs of
securing reliable supplies (Millennium Ecosystem Assessment,
2005b). [WGII 7.4]
In both developed and developing countries, the expected
continuation of rapid population growth in coastal cities will
increase human exposure to flooding and related storm damages
from hurricanes and other coastal storms. [WGII 7.4.2.4] That
very development is contributing to the loss of deltaic wetlands
that could buffer the storm impacts. [WGII 6.4.1.2] In addition,
much of the growth is occurring in relatively water-scarce
coastal areas, thus exacerbating imbalances between water
demand and availability (Small and Nicholls, 2003; Millennium
Ecosystem Assessment, 2005b).
4.5.2
Infrastructure
4.5.2.1 Transportation networks
Flooding due to sea-level rise and increases in the intensity of
extreme weather events (such as storms and hurricanes) pose
threats to transportation networks in some areas. These include
localised street-flooding, flooding of subway systems, and flood
and landslide-related damages to bridges, roads and railways.
For example, in London, which has the world’s oldest subway
system, more intense rainfall events are predicted to increase the
risk of flooding in the Underground and highways. This would
necessitate improvements in the drainage systems of these
networks (Arkell and Darch, 2006). Similarly, recent research
on the surface transportation system of the Boston Metropolitan
Area has predicted that increased flooding will cause increased
trip delays and cancellations, which will result in lost work73
Section 4
Climate change and water resources in systems and sectors
days, sales and production (Suarez et al., 2005). However, those
costs would be small in comparison to flood-related damages
to Boston’s transportation infrastructure (Kirshen et al., 2006).
[WGII 7.4.2.3.3] An example of present-day vulnerability that
could be exacerbated by increased precipitation intensity is
the fact that India’s Konkan Railway annually suffers roughly
US$1 million in damages due to landslides during the rainy
season (Shukla et al., 2005). [WGII 7.4.2.3.3]
4.5.2.2 Built environment
Flooding, landslides and severe storms (such as hurricanes)
pose the greatest risks for damages to buildings in both
developed and developing countries, because housing and other
assets are increasingly located in coastal areas, on slopes, in
ravines and other risk-prone sites (Bigio, 2003; UN-Habitat,
2003). Informal settlements within urban areas of developingcountry cities are especially vulnerable, as they tend to be built
on relatively hazardous sites that are susceptible to floods,
landslides and other climate-related disasters (Cross, 2001;
UN-Habitat, 2003). [WGII 7.4.2.4]
Other impacts on buildings include the potential for accelerated
weathering due to increased precipitation intensity and storm
frequency (e.g., Graves and Phillipson, 2000), and increased
structural damage due to water table decline and subsidence
(e.g., Sanders and Phillipson, 2003), or due to the impacts of a
rising water table (Kharkina, 2004). [WGII 3.5]
Another area of concern is the future performance of stormwater drainage systems. In regions affected by increasingly
intense storms, the capacity of these systems will need to be
increased to prevent local flooding and the resulting damages to
buildings and other infrastructure (UK Water Industry Research,
2004). [WGII 7.6.4]
4.5.2.3 Coastal infrastructure
Infrastructure in low-lying coastal areas is vulnerable to damage
from sea-level rise, flooding, hurricanes and other storms. The
stock of coastal infrastructure at risk is increasing rapidly as a
result of the continuing growth of coastal cities and expanding
tourism in areas such as the Caribbean (e.g., Hareau et al., 1999;
Lewsey et al., 2004; Kumar, 2006). In some areas, damage
costs due to an increase in sea level have been estimated, and
are often substantial. For example, in Poland, estimated damage
costs due to a possible rise in sea level of 1 metre by 2100 are
US$30 billion, due to impacts on urban areas, sewers, ports and
other infrastructure (Zeidler, 1997). The same study estimated
that a projected 1 metre rise in sea level in Vietnam would
subject 17 million people to flooding and cause damages of up
to US$17 billion, with substantial impacts penetrating inland
beyond the coastal zone. [WGII 6.3, 6.4, 6.5]
4.5.2.4 Energy infrastructure
Hydrological changes will directly affect the potential output
of hydro-electric facilities – both those currently existing and
possible future projects. There are large regional differences in
the extent of hydropower development. In Africa, where little
of the continent’s hydropower potential has been developed,
74
climate change simulations for the Batoka Gorge hydro-electric
scheme on the Zambezi River projected a significant reduction
in river flows (e.g., a decline in mean monthly flow from
3.21×109 m3 to 2.07×109 m3) and declining power production
(e.g., a decrease in mean monthly production from 780 GWh
to 613 GWh) (Harrison and Whittington, 2002). A reduction in
hydro-electric power is also anticipated elsewhere, where and
when river flows are expected to decline (e.g., Whittington and
Gundry, 1998; Magadza, 2000). In some other areas, hydroelectric generation is projected to increase. For example,
estimates for the 2070s, under the IS92a emissions scenario,
indicate that the electricity production potential of hydropower
plants existing at the end of the 20th century would increase by
15–30% in Scandinavia and northern Russia, where between
19% (Finland) and almost 100% (Norway) of the electricity
is produced by hydropower (Lehner et al., 2005). [WGII 3.5]
Other energy infrastructure, such as power transmission lines,
offshore drilling rigs and pipelines, may be vulnerable to damage
from flooding and more intense storm events. [WGII 7.5] In
addition, problems with cooling water availability (because of
reduced quantity or higher water temperature) could disrupt
energy supplies by adversely affecting energy production in
thermal and nuclear power plants (EEA, 2005).
4.5.3
Adaptation
The impacts of changes in the frequency of floods and droughts
or in the quantity, quality or seasonal timing of water availability
could be tempered by appropriate infrastructure investments,
and by changes in water and land-use management. Coordinated planning may be valuable because there are many
points at which impacts on the different infrastructures interact.
For instance, the failure of flood defences can interrupt power
supplies, which in turn puts water and wastewater pumping
stations out of action.
Improved incorporation of current climate variability into waterrelated management would make adaptation to future climate
change easier (very high confidence). [WGII 3.6] For example,
managing current flood risks by maintaining green areas and
natural buffers around streams in urban settings would also help
to reduce the adverse impacts of future heavier storm runoff.
However, any of these responses will entail costs, not only in
monetary terms but also in terms of societal impacts, including
the need to manage potential conflicts between different interest
groups. [WGII 3.5]
4.6 Economy: insurance, tourism,
iiiiiiiindustry, transportation
4.6.1
Context
Climate and water resources impact on several secondary and
tertiary sectors of the economy such as insurance, industry,
tourism and transportation. Water-related effects of climate
change in these sectors can be positive as well as negative,
Climate change and water resources in systems and sectors
Section 4
but extreme climate events and other abrupt changes tend to
affect human systems more severely than gradual change, partly
because they offer less time for adaptation. [WGII 7.1.3]
climate-sensitive areas (such as floodplains) (Ruth et al., 2004)
and those dependent on climate-sensitive commodities such as
food-processing plants. [WGII 7.4.2.1]
Global losses reveal rapidly rising costs due to extreme weatherrelated events since the 1970s. One study has found that, while
the dominant signal remains that of the significant increases in
the values of exposure at risk, once losses are normalised for
exposure, there still remains an underlying rising trend. For
specific regions and perils, including the most extreme floods
on some of the largest rivers, there is evidence for an increase
in occurrence. [WGII 1.3.8.5]
The specific insurance risk coverage currently available
within a country will have been shaped by the impact of past
catastrophes. Because of the high concentration of losses due to
catastrophic floods, private-sector flood insurance is generally
restricted (or even unavailable) so that, in several countries,
governments have developed alternative state-backed flood
insurance schemes (Swiss Re, 1998). [WGII 7.4.2.2.4]
To demonstrate the large impact of climate variability on
insurance losses, flooding is responsible for 10% of weatherrelated insurance losses globally. Drought also has an impact:
data from the UK show a lagged relationship between the cost
of insurance claims related to subsidence and (low) summer
rainfall. However, in developing countries, losses due to
extreme events are measured more in terms of human life
than they are in terms of insurance. For example, the Sahelian
drought, despite its high severity, had only a small impact
on the formal financial sector, due to the low penetration of
insurance. [WGII TAR 8.2.3]
4.6.2
Socio-economic costs, mitigation,
adaptation, vulnerability, sustainable
development
Of all the possible water-related impacts on transportation,
the greatest cost is that of flooding. The cost of delays and
lost trips is relatively small compared with damage to the
infrastructure and to other property (Kirshen et al., 2006). In
the last 10 years, there have been four cases when flooding of
urban underground rail systems has caused damages of more
than €10 million (US$13 million) and numerous cases of lesser
damage (Compton et al., 2002). [WGII 7.4.2.3.3]
Industrial sectors are generally thought to be less vulnerable to
the impacts of climate change than such sectors as agriculture.
Among the major exceptions are industrial facilities located in
For the finance sector, climate-change-related risks are
increasingly considered for specific ‘susceptible’ sectors such as
hydro-electric projects, irrigation and agriculture, and tourism
(UNEP/GRID-Arendal, 2002). [WGII 7.4.2.2]
Effects of climate change on tourism include changes in the
availability of water, which could be positive or negative (Braun
et al., 1999; Uyarra et al., 2005). Warmer climates open up the
possibility of extending exotic environments (such as palm
trees in western Europe), which could be considered by some
tourists as positive but could lead to a spatial extension and
amplification of water- and vector-borne diseases. Droughts
and the extension of arid environments (and the effects of
extreme weather events) might discourage tourists, although
it is not entirely clear what they consider to be unacceptable.
[WGII 7.4.2.2.3] Areas dependent on the availability of snow
(e.g., for winter tourism) are among those most vulnerable to
global warming. [WGII 11.4.9, 12.4.9, 14.4.7]
Transportation of bulk freight by inland waterways, such as
the Rhine, can be disrupted during floods and droughts (Parry,
2000). [WGII 7.4.2.2.2]
Insurance spreads risk and assists with adaptation, while
managing insurance funds has implications for mitigation.
[WGII 18.5] Adaptation costs and benefits have been assessed
in a more limited manner for transportation infrastructure (e.g.,
Dore and Burton, 2001). [WGII 17.2.3]
75
5
Analysing regional aspects of
climate change and water resources
Analysing regional aspects of climate change and water resources
Section 5
5.1 Africa
5.1.1
Context
Water is one of several current and future critical issues facing
Africa. Water supplies from rivers, lakes and rainfall are
characterised by their unequal natural geographical distribution
and accessibility, and unsustainable water use. Climate change
has the potential to impose additional pressures on water
availability and accessibility. Arnell (2004) described the
implications of the IPCC’s SRES scenarios for a river-runoff
projection for 2050 using the HadCM320 climate model. These
experiments indicate a significant decrease in runoff in the north
and south of Africa, while the runoff in eastern Africa and parts of
semi-arid sub-Saharan Africa is projected to increase. However,
multi-model results (Figures 2.8 and 2.9) show considerable
variation among models, with the decrease in northern Africa
and the increase in eastern Africa emerging as the most robust
responses. There is a wide spread in projections of precipitation
in sub-Saharan Africa, with some models projecting increases
and others decreases. Projected impacts should be viewed in the
context of this substantial uncertainty. [WGI 11.2, Table 11.1;
WGII 9.4.1]
By 2025, water availability in nine countries21, mainly in
eastern and southern Africa, is projected to be less than
1,000 m3/person/yr. Twelve countries22 would be limited to
1,000–1,700 m3/person/yr, and the population at risk of water
stress could be up to 460 million people, mainly in western
Africa (UNEP/GRID-Arendal, 2002).23 These estimates are
based on population growth rates only and do not take into
account the variation in water resources due to climate change.
In addition, one estimate shows the proportion of the African
population at risk of water stress and scarcity increasing from
47% in 2000 to 65% in 2025 (Ashton, 2002). This could
generate conflicts over water, particularly in arid and semiarid regions. [WGII 9.2, 9.4]
A specific example is the south-western Cape, South Africa,
where one study shows water supply capacity decreasing
either as precipitation decreases or as potential evaporation
increases. This projects a water supply reduction of 0.32%/yr
by 2020, while climate change associated with global warming
is projected to raise water demand by 0.6%/yr in the Cape
Metropolitan Region (New, 2002).
With regard to the Nile Basin, Conway (2005) found that
there is no clear indication of how Nile River flow would be
affected by climate change, because of uncertainty in projected
rainfall patterns in the basin and the influence of complex water
management and water governance structures. [WGII 9.4.2]
Responses to rainfall shifts are already being observed in many
terrestrial water sources that could be considered possible
indicators of future water stress linked to climate variability.
In the eastern parts of the continent, interannual lake level
fluctuations have been observed, with low values in 1993–1997
and higher levels (e.g., of Lakes Tanganyika, Victoria and
Turkana) in 1997–1998, the latter being linked to an excess
in rainfall in late 1997 coupled with large-scale perturbations
in the Indian Ocean (Mercier et al., 2002). Higher water
temperatures have also been reported in lakes in response to
warmer conditions (see Figure 5.1). [WGII 9.2.1.1, 1.3.2.3]
Figure 5.1: Historical and recent measurements from Lake
Tanganyika, East Africa: (a) upper mixed layer (surface water)
temperatures; (b) deep-water (600 m) temperatures; (c) depth
of the upper mixed layer. Triangles represent data collected by
a different method. Error bars represent standard deviations.
Reprinted by permission from Macmillan Publishers Ltd. [Nature]
(O’Reilly et al., 2003), copyright 2003. [WGII Figure 1.2]
5.1.2
Current observations
5.1.2.1
Climate variability
The Sahel region of West Africa experiences marked multidecadal variability in rainfall (e.g., Dai et al., 2004a), associated
with changes in atmospheric circulation and related changes
in tropical sea surface temperature patterns in the Pacific,
Indian and Atlantic Basins (e.g., ENSO and the AMO). Very
See Appendix I for model descriptions.
Djibouti, Cape Verde, Kenya, Burundi, Rwanda, Malawi, Somalia, Egypt and South Africa.
22
Mauritius, Lesotho, Ethiopia, Zimbabwe, Tanzania, Burkina Faso, Mozambique, Ghana, Togo, Nigeria, Uganda and Madagascar.
23
Only five countries in Africa currently (1990 data) have water access volume less than 1,000 m3/person/yr. These are Rwanda, Burundi,
Kenya, Cape Verde and Djibouti.
20
21
79
Analysing regional aspects of climate change and water resources
dry conditions were experienced from the 1970s to the 1990s,
after a wetter period in the 1950s and 1960s. The rainfall deficit
was mainly related to a reduction in the number of significant
rainfall events occurring during the peak monsoon period (July
to September) and during the first rainy season south of about
9°N. The decreasing rainfall and devastating droughts in the
Sahel region during the last three decades of the 20th century
(Figure 5.2) are among the largest climate changes anywhere.
Sahel rainfall reached a minimum after the 1982/83 El Niño
event. [WGI 3.7.4] Modelling studies suggest that Sahel rainfall
has been influenced more by large-scale climate variations
(possibly linked to changes in anthropogenic aerosols), than by
local land-use change. [WGI 9.5.4]
5.1.2.2
Water resources
About 25% of the contemporary African population experiences
water stress, while 69% live under conditions of relative water
abundance (Vörösmarty et al., 2005). However, this relative
abundance does not take into account other factors such as the
extent to which that water is potable and accessible, and the
availability of sanitation. Despite considerable improvements
in access in the 1990s, only about 62% of Africans had access
to improved water supplies in the year 2000 (WHO/UNICEF,
2000). [WGII 9.2.1]
One-third of the people in Africa live in drought-prone areas
and are vulnerable to the impacts of droughts (World Water
Forum, 2000), which have contributed to migration, cultural
separation, population dislocation and the collapse of ancient
cultures. Droughts have mainly affected the Sahel, the Horn
of Africa and southern Africa, particularly since the end of the
1960s, with severe impacts on food security and, ultimately,
the occurrence of famine. In West Africa, a decline in annual
Section 5
rainfall has been observed since the end of the 1960s, with a
decrease of 20–40% in the period 1968–1990 as compared with
the 30 years between 1931 and 1960 (Nicholson et al., 2000;
Chappell and Agnew, 2004; Dai et al., 2004a). The influence of
the ENSO decadal variations has also been recognised in southwest Africa, influenced in part by the North Atlantic Oscillation
(NAO) (Nicholson and Selato, 2000). [WGII 9.2.1]
5.1.2.3
Energy
The electricity supply in the majority of African States is derived
from hydro-electric power. There are few available studies that
examine the impacts of climate change on energy use in Africa
(Warren et al., 2006). [WGII 9.4.2] Nevertheless, the continent
is characterised by a high dependency on fuelwood as a major
source of energy in rural areas – representing about 70% of total
energy consumption in the continent. Any impact of climate
change on biomass production would, in turn, impact on the
availability of wood-fuel energy. Access to energy is severely
constrained in sub-Saharan Africa, with an estimated 51% of
urban populations and only 8% of rural populations having
access to electricity. This can be compared with the 99% of
urban populations and 80% of rural populations that have
access in northern Africa. Further challenges from urbanisation,
rising energy demands and volatile oil prices further compound
energy issues in Africa. [WGII 9.2.2.8]
5.1.2.4
Health
Malaria
The spatial distribution, intensity of transmission, and
seasonality of malaria is influenced by climate in sub-Saharan
Africa; socio-economic development has had only limited
impact on curtailing disease distribution (Hay et al., 2002a;
Craig et al., 2004). [WGII 8.2.8.2]
Figure 5.2: Time-series of Sahel (10°N–20°N, 18°W–20°E) regional rainfall (April–October) from 1920 to 2003 derived
from gridding normalised station anomalies and then averaging using area weighting (adapted from Dai et al., 2004a).
Positive values (shaded bars) indicate conditions wetter than the long-term mean and negative values (unfilled bars) indicate
conditions drier than the long-term mean. The smooth black curve shows decadal variations. [WGI Figure 3.37]
80
Section 5
Analysing regional aspects of climate change and water resources
Rainfall can be a limiting factor for mosquito populations and
there is some evidence of reductions in transmission associated
with decadal decreases in rainfall. Evidence of the predictability
of unusually high or low malaria anomalies from both sea
surface temperature (Thomson et al., 2005b) and multi-model
ensemble seasonal climate forecasts in Botswana (Thomson
et al., 2006) supports the practical and routine use of seasonal
forecasts for malaria control in southern Africa (DaSilva et al.,
2004). [WGII 8.2.8.2]
The effects of observed climate change on the geographical
distribution of malaria and its transmission intensity in highland
regions remains controversial. Analyses of time-series data in
some sites in East Africa indicate that malaria incidence has
increased in the apparent absence of climate trends (Hay et al.,
2002a, b; Shanks et al., 2002). The suggested driving forces
behind the resurgence of malaria include drug resistance of
the malaria parasite and a decrease in vector control activities.
However, the validity of this conclusion has been questioned
because it may have resulted from inappropriate use of the
climatic data (Patz, 2002). Analysis of updated temperature data
for these regions has found a significant warming trend since
the end of the 1970s, with the magnitude of the change affecting
transmission potential (Pascual et al., 2006). In southern Africa,
long-term trends for malaria were not significantly associated
with climate, although seasonal changes in case numbers were
significantly associated with a number of climatic variables
(Craig et al., 2004). Drug resistance and HIV infection were
associated with long-term malaria trends in the same area (Craig
et al., 2004). [WGII 8.2.8.2]
A number of further studies have reported associations between
interannual variability in temperature and malaria transmission
in the African highlands. An analysis of de-trended time-series
malaria data in Madagascar indicated that minimum temperature
at the start of the transmission season, corresponding to the
months when the human–vector contact is greatest, accounts for
most of the variability between years (Bouma, 2003). In highland
areas of Kenya, malaria admissions have been associated with
rainfall and unusually high maximum temperatures 3–4 months
previously (Githeko and Ndegwa, 2001). An analysis of malaria
morbidity data for the period from the late 1980s until the early
1990s from 50 sites across Ethiopia found that epidemics were
associated with high minimum temperatures in the preceding
months (Abeku et al., 2003). An analysis of data from seven
highland sites in East Africa reported that short-term climate
variability played a more important role than long-term trends in
initiating malaria epidemics (Zhou et al., 2004, 2005), although
the method used to test this hypothesis has been challenged
(Hay et al., 2005). [WGII 8.2.8.2]
Other water-related diseases
While infectious diseases such as cholera are being eradicated
in other parts of the world, they are re-emerging in Africa. Child
mortality due to diarrhoea in low-income countries, especially
in sub-Saharan Africa, remains high despite improvements in
care and the use of oral rehydration therapy (Kosek et al.,
2003). Children may survive the acute illness but may later
die due to persistent diarrhoea or malnutrition. Several studies
have shown that transmission of enteric pathogens is higher
during the rainy season (Nchito et al., 1998; Kang et al., 2001).
[WGII 8.2.5, 9.2.2.6]
5.1.2.5
Agricultural sector
The agricultural sector is a critical mainstay of local livelihoods
and national GDP in some countries in Africa. Agriculture
contributions to GDP vary across countries, but assessments
suggest an average contribution of 21% (ranging from 10% to
70%) (Mendelsohn et al., 2000b). Even where the contribution
of agriculture to GDP is low, the sector may still support the
livelihoods of very large sections of the population, so that
any reduction in output will have impacts on poverty and food
security. This sector is particularly sensitive to climate, including
periods of climate variability. In many parts of Africa, farmers
and pastoralists also have to contend with other extreme natural
resource challenges and constraints such as poor soil fertility,
pests, crop diseases and a lack of access to inputs and improved
seeds. These challenges are usually aggravated by periods of
prolonged droughts and floods (Mendelsohn et al., 2000a, b;
Stige et al., 2006). [WGII 9.2.1.3]
5.1.2.6
Ecosystems and biodiversity
Ecosystems and their biodiversity contribute significantly
to human well-being in Africa. [WGII Chapter 9] The rich
biodiversity in Africa, which occurs principally outside formally
conserved areas, is under threat from climate variability and
change and other stresses (e.g., Box 5.1). Africa’s social and
economic development is constrained by climate change,
habitat loss, over-harvesting of selected species, the spread of
alien species, and activities such as hunting and deforestation,
which threaten to undermine the integrity of the continent’s
rich but fragile ecosystems (UNEP/GRID-Arendal, 2002).
Approximately half of the sub-humid and semi-arid parts of the
southern African region, for example, are at moderate to high
risk of desertification. In West Africa, the long-term decline in
rainfall from the 1970s to the 1990s has caused a 25–35 km shift
southward in the Sahel, Sudan and Guinean ecological zones in
the second half of the 20th century (Gonzalez, 2001). This has
resulted in the loss of grassland and acacia, loss of flora/fauna,
and shifting sand dunes in the Sahel; effects that are already being
observed (ECF and Potsdam Institute, 2004). [WGII 9.2.1.4]
5.1.3
Projected changes
5.1.3.1
Water resources
Increased populations in Africa are expected to experience
water stress before 2025, i.e., in less than two decades
from the publication of this report, mainly due to increased
water demand. [WGII 9.4.1] Climate change is expected to
exacerbate this condition. In some assessments, the population
at risk of increased water stress in Africa, for the full range
of SRES scenarios, is projected to be 75–250 million and
350–600 million people by the 2020s and 2050s, respectively
(Arnell, 2004). However, the impact of climate change on water
resources across the continent is not uniform. An analysis of
six climate models (Arnell, 2004) shows a likely increase in the
81
Section 5
Analysing regional aspects of climate change and water resources
Box 5.1: Environmental changes on Mt. Kilimanjaro. [Adapted from WGII Box 9.1]
There is evidence that climate change is modifying natural mountain ecosystems on Mt. Kilimanjaro. For example, as a
result of dry climatic conditions, the increased frequency and intensity of fires on the slopes of Mt. Kilimanjaro led to a
downward shift of the upper forest line by several hundreds of metres during the 20th century (Figure 5.3, Table 5.1). The
resulting decrease in cloud-forest cover by 150 km2 since 1976 has had a major impact on the capturing of fog as well as
on the temporary storage of rain, and thus on the water balance of the mountain (Hemp, 2005).
Figure 5.3: Land cover changes induced by complex land use and climate interactions on Kilimanjaro (Hemp, 2005).
Reprinted by permission from Blackwell Publishing Ltd.
Table 5.1: Land cover changes in the upper regions of Kilimanjaro (Hemp, 2005).
Vegetation type
Area 1976 (km2)
Area 2000 (km2)
Change (%)
Montane forest
1066
974
-9
Subalpine Erica forest
187
32
-83
Erica bush
202
257
+27
Helichrysum cushion
vegetation
Grassland
69
218
+216
90
44
-51
number of people who could experience water stress by 2055
in northern and southern Africa (Figure 5.4). In contrast, more
people in eastern and western Africa will be likely to experience
a reduction rather than an increase in water stress (Arnell,
2006a). [WGII 3.2, Figure 3.2, Figure 3.4, 9.4.1, Figure 9.3]
Groundwater is most commonly the primary source of drinking
water in Africa, particularly in rural areas which rely on low-cost
dug wells and boreholes. Its recharge is projected to decrease
with decreased precipitation and runoff, resulting in increased
water stress in those areas where groundwater supplements
dry season water demands for agriculture and household use.
[WGII 3.4.2, Figure 3.5]
82
A study of the impacts of a 1°C temperature increase in one
watershed in the Maghreb region projects a runoff deficit of
some 10% (Agoumi, 2003), assuming precipitation levels
remain constant. [WGII 9.4.1, 3.2, 3.4.2]
5.1.3.2
Energy
Although not many energy studies have been undertaken for
Africa, a study of hydro-electric power generation conducted
in the Zambezi Basin, taken in conjunction with projections
of future runoff, indicate that hydropower generation would
be negatively affected by climate change, particularly in river
basins that are situated in sub-humid regions (Riebsame et al.,
1995; Salewicz, 1995). [WGII TAR 10.2.11, Table 10.1]
Section 5
Analysing regional aspects of climate change and water resources
Figure 5.4: Number of people (millions) living in watersheds exposed to an increase in water stress, compared to 1961–1990
(Arnell, 2006b). Water-stressed watersheds have runoff less than 1,000 m3/capita/yr, and populations are exposed to an
increase in water stress when runoff reduces significantly, due to climate change. Scenarios are derived from HadCM3
and the red, green and blue lines relate to different population projections; note that projected hydrological changes vary
substantially between different climate models in some regions. The steps in the function occur as more watersheds experience
a significant decrease in runoff. [WGII Figure 9.3]
5.1.3.3
Health
A considerable number of studies have linked climate change
with health issues in the continent. For example, results from
the Mapping Malaria Risk in Africa project (MARA/ARMA)
indicate changes in the distribution of climate-suitable areas for
malaria by 2020, 2050 and 2080 (Thomas et al., 2004). By 2050,
and continuing into 2080, a large part of the western Sahel and
much of southern-central Africa is shown to be likely to become
unsuitable for malaria transmission. Other assessments (e.g.,
Hartmann et al., 2002), using sixteen climate change scenarios,
show that, by 2100, changes in temperature and precipitation
could alter the geographical distribution of malaria in Zimbabwe,
with previously unsuitable areas of dense human population
becoming suitable for transmission. [WGII 9.4.3]
Relatively few assessments of the possible future changes in
animal health arising from climate variability and change
have been undertaken. Changes in disease distribution, range,
prevalence, incidence and seasonality can be expected. However,
there is low certainty about the degree of change. Rift Valley
Fever epidemics, evident during the 1997/98 El Niño event
in East Africa and associated with flooding, could increase in
regions subject to increases in flooding (Section 3.2.1.2). The
number of extremely wet seasons in East Africa is projected
to increase. Finally, heat stress and drought are likely to have
a further negative impact on animal health and the production
of dairy products (this has already been observed in the USA;
see Warren et al., 2006). [WGI Table 11.1, 11.2.3; WGII 9.4.3,
5.4.3.1]
5.1.3.4
Agriculture
Impacts of climate change on growing periods and on
agricultural systems and possible livelihood implications have
been examined (e.g., Thornton et al., 2006). A recent study
based on three scenarios indicates that crop net revenues would
be likely to fall by as much as 90% by 2100, with small-scale
farms being the most affected. However, there is the possibility
that adaptation could reduce these negative effects (Benhin,
2006). [WGII 9.4.4]
A case study of climate change, water availability and agriculture
in Egypt is provided in Box 5.2.
Not all changes in climate and climate variability would,
however, be negative for agriculture. The growing seasons in
certain areas, such as around the Ethiopian highlands, may
lengthen under climate change. A combination of increased
temperatures and rainfall changes may lead to the extension of
the growing season, for example in some of the highland areas
(Thornton et al., 2006). As a result of a reduction in frost in the
highland zones of Mt. Kenya and Mt. Kilimanjaro, for example,
it may be possible to grow more temperate crops, e.g., apples,
pears, barley, wheat, etc. (Parry et al., 2004). [WGII 9.4.4]
Fisheries are another important source of revenue, employment,
and protein. In coastal regions that have major lagoons or lake
systems, changes in freshwater flows, and more intrusion of
saltwaters into the lagoons, would affect species that are the
basis of inland fisheries or aquaculture (Cury and Shannon,
2004). [WGII 9.4.4]
The impact of climate change on livestock in Africa has been
examined (Seo and Mendelsohn, 2006). Decreased precipitation
of 14% would be likely to reduce large farm livestock income by
about 9% (−US$5 billion) due to a reduction in both the stock
numbers and the net revenue per animal owned. [WGII 9.4.4]
83
Analysing regional aspects of climate change and water resources
Section 5
Box 5.2: Climate, water availability and agriculture in Egypt. [WGII Box 9.2]
Egypt is one of the African countries that could be vulnerable to water stress under climate change. The water used in
2000 was estimated at about 70 km3 which is already far in excess of the available resources (Gueye et al., 2005). A
major challenge is to close the rapidly increasing gap between the limited water availability and the escalating demand for
water from various economic sectors. The rate of water utilisation has already reached its maximum for Egypt, and climate
change will exacerbate this vulnerability.
Agriculture consumes about 85% of the annual total water resource and plays a significant role in the Egyptian national
economy, contributing about 20% of GDP. More than 70% of the cultivated area depends on low-efficiency surface
irrigation systems, which cause high water losses, a decline in land productivity, waterlogging and salinity problems (ElGindy et al., 2001). Moreover, unsustainable agricultural practices and improper irrigation management affect the quality
of the country’s water resources. Reductions in irrigation water quality have, in their turn, harmful effects on irrigated soils
and crops.
Institutional water bodies in Egypt are working to achieve the following targets by 2017 through the National Improvement
Plan (EPIQ, 2002; ICID, 2005):
•
improving water sanitation coverage for urban and rural areas,
•
wastewater management,
•
optimising the use of water resources by improving irrigation efficiency and agriculture drainage-water reuse.
However, with climate change, an array of serious threats is apparent.
•
Sea-level rise could impact on the Nile Delta and on people living in the delta and other coastal areas (Wahab,
2005).
•
Temperature rises will be likely to reduce the productivity of major crops and increase their water requirements,
thereby directly decreasing crop water-use efficiency (Abou-Hadid, 2006; Eid et al., 2006).
•
There will probably be a general increase in irrigation demand (Attaher et al., 2006).
•
There will also be a high degree of uncertainty about the flow of the Nile.
•
Based on SRES scenarios, Egypt will be likely to experience an increase in water stress, with a projected decline
in precipitation and a projected population of between 115 and 179 million by 2050. This will increase water stress
in all sectors.
•
Ongoing expansion of irrigated areas will reduce the capacity of Egypt to cope with future fluctuations in flow
(Conway, 2005).
5.1.3.5
Biodiversity
Soil moisture reduction due to precipitation changes could
affect natural systems in several ways. There are projections
of significant extinctions in both plant and animals species.
Over 5,000 plant species could be impacted by climate change,
mainly due to the loss of suitable habitats. By 2050, the Fynbos
Biome (Ericaceae-dominated ecosystem of South Africa, which
is an IUCN ‘hotspot’) is projected to lose 51–61% of its extent
due to decreased winter precipitation. The succulent Karoo
Biome, which includes 2,800 plant species at increased risk of
extinction, is projected to expand south-eastwards, and about 2%
of the family Proteaceae are projected to become extinct. These
plants are closely associated with birds that have specialised
on feeding on them. Some mammal species, such as the zebra
and nyala, which have been shown to be vulnerable to droughtinduced changes in food availability, are widely projected to
suffer losses. In some wildlife management areas, such as the
Kruger and Hwange National Parks, wildlife populations are
already dependant on water supplies supplemented by borehole
water (Box 5.3). [WGII 4.4, 9.4.5, Table 9.1]
84
Box 5.3: Projected extinctions in the Kruger
National Park, South Africa. [WGII Table 4.1]
In the Kruger National Park, South Africa, and for a
global mean temperature increase 2.5–3.0°C above
1990 levels:
• 24–59% of mammals,
• 28–40% of birds,
• 13–70% of butterflies,
• 18–80% of other invertebrates, and
• 21–45% of reptiles would be committed to
extinction.
In total, 66% of animal species would potentially be lost.
Many bird species are migrants from Europe and the PalaeoArctic region. Some species use the southern Sahel as a stopover
stage before crossing the Sahara Desert. Drought-induced food
shortage in the region would impair the migration success of
Analysing regional aspects of climate change and water resources
Section 5
such birds. As noted, the precipitation models for the Sahel are
equivocal. [WGII 9.3.1] If the wet scenarios materialise, then the
biodiversity of the sub-Saharan/Sahel region is in no imminent
danger from water-stress-related impacts. On the other hand, the
drier scenario would, on balance, lead to extensive extinctions,
especially as competition between natural systems and human
needs would intensify. [WGII 9.4.5]
Simulation results for raptors in southern Africa, using
precipitation as the key environmental factor, suggest significant
range reductions as their current ranges become drier. [WGII
4.4.3] In all, it is expected that about 25–40% of sub-Saharan
African animal species in conservation areas would be
endangered. [WGII 9.4.5]
5.1.4
Adaptation and vulnerability
Recent studies in Africa highlight the vulnerability of local
groups that depend primarily on natural resources for their
livelihoods, indicating that their resource base – already
severely stressed and degraded by overuse – is expected to
be further impacted by climate change (Leary et al., 2006).
[WGII 17.1]
Climate change and variability have the potential to impose
additonal pressures on water availability, accessibility, supply
and demand in Africa. [WGII 9.4.1] It is estimated that around
25% (200 million) of Africa’s population currently experiences
water stress, with more countries expected to face high future
risk (see Section 5.1.3.1). [WGII 9.ES] Moreover, it has been
envisioned that, even without climate change, several countries,
particularly in northern Africa, would reach the threshold level
of their economically usable land-based water resources before
2025. [WGII 9.4.1] Frequent natural disasters, such as droughts
and floods, have largely constrained agricultural development in
Africa, which is heavily dependent on rainfall, leading to food
insecurity in addition to a range of macro- and microstructural
problems. [WGII 9.5.2]
ENSO has a significant influence on rainfall at interannual
scales in Africa and may influence future climate variability.
[WGI 3.7.4, 3.6.4, 11.2] However, a number of barriers hamper
effective adaptation to variations in ENSO including: spatial
and temporal uncertainties associated with forecasts of regional
climate; the low level of awareness among decision makers
of the local and regional impacts of El Niño; limited national
capacities in climate monitoring and forecasting; and lack of
co-ordination in the formulation of responses (Glantz, 2001).
[WGII 17.2.2]
Regarding the impacts of climate variability and change on
groundwater, little information is available, despite many
countries (especially in northern Africa) being dependent on
such water sources. [WGII 9.2.1]
Previous assessments of water impacts have not adequately
covered the multiple future water uses and future water stress
(e.g., Agoumi, 2003; Conway, 2005), and so more detailed
research on hydrology, drainage and climate change is required.
Future access to water in rural areas, drawn from low-order
surface water streams, also needs to be addressed by countries
sharing river basins (e.g., de Wit and Stankiewicz, 2006).
[WGII 9.4.1]
Adaptive capacity and adaptation related to water resources are
considered very important to the African continent. Historically,
migration in the face of drought and floods has been identified
as one of the adaptation options. Migration has also been found
to present a source of income for those migrants, who are
employed as seasonal labour. Other practices that contribute
to adaptation include traditional and modern water-harvesting
techniques, water conservation and storage, and planting of
drought-resistant and early-maturing crops. The importance of
building on traditional knowledge related to water harvesting
and use has been highlighted as one of the most important
adaptation requirements (Osman-Elasha et al., 2006), indicating
the need for its incorporation into climate change policies to
ensure the development of effective adaptation strategies that
are cost-effective, participatory and sustainable. [WGII 9.5.1,
Table 17.1]
Very little information exists regarding the cost of impacts and
adaptation to climate change for water resources in Africa.
However, an initial assessment in South Africa of adaptation
costs in the Berg River Basin shows that the costs of not adapting
to climate change can be much greater than those that may arise
if flexible and efficient approaches are included in management
options (see Stern, 2007). [WGII 9.5.2]
5.2 Asia
5.2.1
Context
Asia is a region where water distribution is uneven and large
areas are under water stress. Among the forty-three countries of
Asia, twenty have renewable annual per capita water resources
in excess of 3,000 m3, eleven are between 1,000 and 3,000 m3,
and six are below 1,000 m3 (there are no data from the remaining
six countries) (FAO, 2004a, b, c). [WGII Table 10.1] From west
China and Mongolia to west Asia, there are large areas of arid
and semi-arid lands. [WGII 10.2] Even in humid and sub-humid
areas of Asia, water scarcity/stress is one of the constraints for
sustainable development. On the other hand, Asia has a very
high population that is growing at a fast rate, low development
levels and weak coping capacity. Climate change is expected
to exacerbate the water scarcity situation in Asia, together with
multiple socio-economic stresses. [WGII 10.2]
5.2.2
Observed impacts of climate change on water
5.2.2.1
Freshwater resources
Inter-seasonal, interannual, and spatial variability in rainfall
has been observed during the past few decades across all of
Asia. Decreasing trends in annual mean rainfall were observed
in Russia, north-east and north China, the coastal belts and
85
Analysing regional aspects of climate change and water resources
Section 5
arid plains of Pakistan, parts of north-east India, Indonesia,
the Philippines and some areas of Japan. Annual mean rainfall
exhibits increasing trends in western China, the Changjiang
(River Yangtze) Basin and the south-eastern coast of China, the
Arabian Peninsula, Bangladesh and along the western coasts
of the Philippines. In South-East Asia, extreme weather events
associated with El Niño have been reported to be more frequent
and intense in the past 20 years (Trenberth and Hoar, 1997;
Aldhous, 2004). It is important to note that substantial interdecadal variability exists in both the Indian and the east Asian
monsoons. [WGI 3.3.2, 3.7.1; WGII 10.2.2, 10.2.3]
Generally, the frequency of occurrence of more intense rainfall
events in many parts of Asia has increased, causing severe
floods, landslides, and debris and mud flows, while the number
of rainy days and total annual amount of precipitation have
decreased (Zhai et al., 1999; Khan et al., 2000; Shrestha et
al., 2000; Izrael and Anokhin, 2001; Mirza, 2002; Kajiwara
et al., 2003; Lal, 2003; Min et al., 2003; Ruosteenoja et al.,
2003; Zhai and Pan, 2003; Gruza and Rankova, 2004; Zhai,
2004). However, there are reports that the frequency of extreme
rainfall in some countries has exhibited a decreasing tendency
(Manton et al., 2001; Kanai et al., 2004). [WGII 10.2.3]
The increasing frequency and intensity of droughts in many
parts of Asia are attributed largely to rising temperatures,
particularly during the summer and normally drier months,
and during ENSO events (Webster et al. 1998; Duong, 2000;
PAGASA, 2001; Lal, 2002, 2003; Batima, 2003; Gruza and
Rankova, 2004; Natsagdorj et al., 2005). [WGI Box 3.6;
WGII 10.2.3]
Rapid thawing of permafrost and decreasing depth of frozen
soils [WGI 4.7.2], due largely to warming, has threatened
many cities and human settlements, has caused more frequent
landslides and degeneration of some forest ecosystems, and has
resulted in an increase in lake water levels in the permafrost
region of Asia (Osterkamp et al., 2000; Guo et al., 2001; Izrael
and Anokhin, 2001; Jorgenson et al., 2001; Izrael et al., 2002;
Fedorov and Konstantinov, 2003; Gavriliev and Efremov, 2003;
Melnikov and Revson, 2003; Nelson, 2003; Tumerbaatar, 2003;
ACIA, 2005). [WGII 10.2.4.2]
On average, Asian glaciers are melting at a rate that has been
constant since at least the 1960s (Figure 2.6). [WGI 4.5.2]
However, individual glaciers may vary from this pattern, and
some are actually advancing and/or thickening – for example, in
the central Karakorum – probably due to enhanced precipitation
(Hewitt, 2005). [WGI 4.5.3] As a result of the ongoing melting
of glaciers, glacial runoff and the frequency of glacial lake
outbursts, causing mudflows and avalanches, have increased
(Bhadra, 2002; WWF, 2005). [WGII 10.2.4.2]
Figure 5.5 shows the retreat (since 1780) of the Gangotri
Glacier, the source of the Ganges, located in Uttarakhand, India.
Although this retreat has been linked to anthropogenic climate
change, no formal attribution studies have been carried out. It is
worth noting that the tongue of this particular glacier is rather
86
Figure 5.5: Composite satellite image showing how
the Gangotri Glacier (source of the Ganges, located in
Uttarakhand, India) terminus has retracted since 1780
(courtesy of NASA EROS Data Center, 9 September, 2001).
[WGII Figure 10.6]
flat and heavily covered in debris. The shrinkage of tongues
with these characteristics is difficult to relate to a particular
climate signal, since the debris cover delays any signal. Flat
tongues tend to collapse suddenly, with a sudden change in
area, after thinning out for decades with relatively little areal
change. [WGII 10.6.2]
In parts of China, temperature increases and decreases in
precipitation, along with increasing water use, have caused
water shortages that have led to drying up of lakes and rivers.
In India, Pakistan, Nepal and Bangladesh, water shortages
have been attributed to issues such as rapid urbanisation and
industrialisation, population growth and inefficient water use,
which are all aggravated by changing climate and its adverse
impacts on demand, supply and water quality. In the countries
situated in the Brahmaputra–Ganges–Meghna and Indus Basins,
water shortages are also the result of the actions of upstream
riverside-dwellers in storing water. In arid and semi-arid central
and west Asia, changes in climate and its variability continue to
challenge the ability of countries to meet growing demands for
water (Abu-Taleb, 2000; Ragab and Prudhomme, 2002; BouZeid and El-Fadel, 2002; UNEP/GRID-Arendal, 2002). The
decreased precipitation and increased temperature commonly
associated with ENSO have been reported to increase water
shortages, particularly in parts of Asia where water resources
are already under stress from growing water demands and
inefficient water use (Manton et al., 2001). [WGII 10.2.4.2]
Section 5
Analysing regional aspects of climate change and water resources
5.2.2.2
Agriculture
Production of rice, maize and wheat in the past few decades
has declined in many parts of Asia due to increasing
water stress, arising partly from increasing temperatures,
increasing frequency of El Niño events and reductions in
the number of rainy days (Wijeratne, 1996; Agarwal et al.,
2000; Jin et al., 2001; Fischer et al., 2002a; Tao et al., 2003a,
2004). [WGII 10.2.4.1]
5.2.2.3
Biodiversity
With the gradual reduction in rainfall during the growing season
for grass, aridity in central and west Asia has increased in
recent years, reducing the growth of grasslands and increasing
the bareness of the ground surface (Bou-Zeid and El-Fadel,
2002). Increasing bareness has led to increased reflection of
solar radiation, such that more soil moisture evaporates and the
ground becomes increasingly drier in a feedback process, thus
adding to the acceleration of grassland degradation (Zhang et
al., 2003). [WGII 10.2.4.4]
Precipitation decline and droughts in most delta regions of
Pakistan, Bangladesh, India and China have resulted in drying
of wetlands and severe degradation of ecosystems. The recurrent
droughts from 1999 to 2001, as well as construction of upstream
reservoirs and improper use of groundwater, have led to drying
of the Momoge Wetland located in the Songnen Plain in northeastern China (Pan et al., 2003). [WGII 10.2.4.4]
5.2.3
Projected impact of climate change on
iiiiiiiiiiiiiiiiwater and key vulnerabilities
5.2.3.1
Freshwater resources
Changes in seasonality and amount of water flow from river
systems are expected, due to climate change. In some parts of
Russia, climate change could significantly alter the variability
of river runoff such that extremely low runoff events might
occur much more frequently in the crop growing regions of the
south-west (Peterson et al., 2002). Surface water availability
from major rivers such as the Euphrates and Tigris might be
affected by alteration of river flow. In Lebanon, the annual net
usable water resource would decrease by 15% in response to a
GCM-estimated average rise in temperature of 1.2°C under a
doubled-CO2 climate, while the flows in rivers would increase
in winter and decrease in spring (Bou-Zeid and El-Fadel, 2002).
The maximum monthly flow of the Mekong is projected to
increase by 35–41% in the basin and by 16–19% in the delta,
with the lower value estimated for the years 2010–2038 and
the higher value for the years 2070–2099, compared with
1961–1990 levels. In contrast, the minimum monthly flows are
estimated to decline by 17–24% in the basin and 26–29% in the
delta (Hoanh et al., 2004) [WGII Box 5.3], suggesting that there
could be increased flooding risks during the wet season and
an increased possibility of water shortages in the dry season.
[WGII 10.4.2.1]
Flooding could increase the habitat of brackish-water fisheries
but could also seriously affect the aquaculture industry and
infrastructure, particularly in heavily populated megadeltas.
Reductions in dry-season flows may reduce recruitment of
some species. In parts of central Asia, regional increases in
temperature are expected to lead to an increased probability of
events such as mudflows and avalanches that could adversely
affect human settlements (Iafiazova, 1997). [WGII 10.4.2.1]
Saltwater intrusion in estuaries due to decreasing river runoff can
be pushed 10–20 km further inland by rising sea levels (Shen et
al., 2003; Yin et al., 2003; Thanh et al., 2004). Increases in water
temperature and eutrophication in the Zhujiang and Changjiang
Estuaries have led to formation of a bottom oxygen-deficient
horizon and increased frequency and intensity of ‘red tides’ (Hu
et al., 2001). Sea-level rises of 0.4–1.0 m can induce saltwater
intrusion 1–3 km further inland in the Zhujiang Estuary (Huang
and Xie, 2000). Increasing frequency and intensity of droughts
in the catchment area would lead to more serious and frequent
saltwater intrusion in the estuary (Xu, 2003; Thanh et al., 2004;
Huang et al., 2005) and thus deteriorate surface water and
groundwater quality. [WGII 10.4.2.1, 10.4.3.2]
Consequences of enhanced snow and glacier melt, as well
as rising snow lines, would be unfavourable for downstream
agriculture in several countries of south and central Asia. The
volume and rate of snowmelt in spring is projected to accelerate
in north-western China and western Mongolia and the thawing
time could advance, which will increase some water sources
and may lead to flood in spring, but significant shortages in
water availability for livestock are projected by the end of this
century (Batima et al., 2004, 2005). [WGII 10.4.2, 10.6]
It is expected that, in the medium term, climate-change-driven
enhanced snow- or glacier melt will lead to floods. Such
floods quite often are caused by rising river water levels due to
blockage of the channel by drifting ice. [WGII 10.4.2, 10.6]
A projected increase in surface air temperature in north-western
China is, by linear extrapolation of observed changes, expected
to result in a 27% decline in glacier area, a 10–15% decline in
frozen soil area, an increase in flood and debris flow, and more
severe water shortages by 2050 compared with 1961–1990
(Qin, 2002). The duration of seasonal snow cover in alpine
areas – namely the Tibet Plateau, Xinjiang and Inner Mongolia
– is expected to shorten, leading to a decline in volume and
resulting in severe spring droughts. Between 20% and 40%
reductions in runoff per capita in Ningxia, Xinjiang and Qinghai
Provinces are likely by the end of the 21st century (Tao et al.,
2005). However, pressure on water resources due to increasing
population and socio-economic development is likely to grow.
Higashi et al. (2006) project that the future flood risk in Tokyo
(Japan) between 2050 and 2300 under the SRES A1B scenario
is likely to be 1.1 to 1.2 times higher than the present condition.
[WGII 10.4.2.3]
The gross per capita water availability in India is projected
to decline from about 1,820 m3/yr in 2001 to as little as
1,140 m3/yr in 2050, as a result of population growth (Gupta
and Deshpande, 2004). Another study indicates that India will
87
Analysing regional aspects of climate change and water resources
reach a state of water stress before 2025, when the availability
is projected to fall below 1,000 m3 per capita (CWC, 2001).
These changes are due to climatic and demographic factors.
The relative contribution of these factors is not known. The
projected decrease in winter precipitation over the Indian subcontinent would imply less storage and greater water stress
during the lean monsoon period. Intense rain occurring over
fewer days, which implies increased frequency of floods during
the monsoon, may also result in reduced groundwater recharge
potential. Expansion of areas under severe water stress will
be one of the most pressing environmental problems in South
and South-East Asia in the foreseeable future, as the number
of people living under severe water stress is likely to increase
substantially in absolute terms. It is estimated that, under the
full range of SRES scenarios, from 120 million to 1.2 billion,
and from 185 million to 981 million people will experience
increased water stress by the 2020s and the 2050s, respectively
(Arnell, 2004). The decline in annual flow of the Red River by
13–19% and that of the Mekong River by 16–24% by the end of
the 21st century is projected, and would contribute to increasing
water stress (ADB, 1994). [WGII 10.4.2]
5.2.3.2
Energy
Changes in runoff could have a significant effect on the power
output of hydropower-generating countries such as Tajikistan,
which is the third largest hydro-electricity producer in the world
(World Bank, 2002). [WGII 10.4.2]
5.2.3.3
Agriculture
Agricultural irrigation demand in arid and semi-arid regions of
Asia is estimated to increase by at least 10% for an increase in
temperature of 1°C (Fischer et al., 2002a; Liu, 2002). Based on a
study by Tao et al. (2003b), rain-fed crops in the plains of north
and north-east China could face water-related challenges in future
decades due to increases in water demand and soil-moisture
deficit associated with projected declines in precipitation. Note,
however, that more than two-thirds of the models ensembled in
Figures 2.8 and 2.10 show an increase in precipitation and runoff
for this region. In north China, irrigation from surface water
and groundwater sources is projected to meet only 70% of the
water requirement for agricultural production, due to the effects
of climate change and increasing demand (Liu et al., 2001; Qin,
2002). [WGII 10.4.1] Enhanced variability in hydrological
characteristics will be likely to continue to affect grain supplies
and food security in many nations of Asia. [WGII 10.4.1.2]
5.2.4
Adaptation and vulnerability
There are different current water vulnerabilities in Asian
countries. Some countries which are not currently facing high
risk are expected to face a future risk of water stress, with various
capacities for adaptation. Coastal areas, especially heavily
populated megadelta regions in south, east and south-east Asia,
are expected to be at greatest risk of increased river and coastal
flooding. In southern and eastern Asia, the interaction of climate
change impacts with rapid economic and population growth,
and migration from rural to urban areas, is expected to affect
development. [WGII 10.2.4, 10.4, 10.6]
88
Section 5
The vulnerability of a society is influenced by its development
path, physical exposures, the distribution of resources, prior
stresses, and social and government institutions. All societies
have inherent abilities to deal with certain variations in climate,
yet adaptive capacities are unevenly distributed, both across
countries and within societies. The poor and marginalised
have historically been most at risk, and are most vulnerable to
the impacts of climate change. Recent analyses in Asia show
that marginalised, primary-resource-dependent livelihood
groups are particularly vulnerable to climate change impacts
if their natural resource base is severely stressed and degraded
by overuse, or if their governance systems are not capable of
responding effectively (Leary et al., 2006). [WGII 17.1] There
is growing evidence that adaptation is occurring in response
to observed and anticipated climate change. For example,
climate change forms part of the design consideration in
infrastructure projects such as coastal defence in the Maldives
and prevention of glacial lake outburst flooding in Nepal (see
Box 5.4). [WGII 17.2, 17.5, 16.5]
In some parts of Asia, the conversion of cropland to forest
(grassland), restoration and re-establishment of vegetation,
improvement of the tree and herb varieties, and selection and
cultivation of new drought-resistant varieties could be effective
measures to prevent water scarcity due to climate change. Watersaving schemes for irrigation could be used to avert the water
scarcity in regions already under water stress (Wang, 2003). In
north Asia, recycling and reuse of municipal wastewater (Frolov
et al., 2004) and increasing efficiency of water use for irrigation
and other purposes (Alcamo et al., 2004) will be likely to help
avert water scarcity. [WGII 10.5.2]
There are many adaptation measures that could be applied in
various parts of Asia to minimise the impacts of climate change
on water resources, several of which address the existing
inefficiency in the use of water:
•
modernisation of existing irrigation schemes and demand
management aimed at optimising physical and economic
efficiency in the use of water resources and recycled water
in water-stressed countries;
•
public investment policies that improve access to available
water resources, encourage integrated water management
and respect for the environment, and promote better
practices for the sensible use of water in agriculture;
•
the use of water to meet non-potable water demands. After
treatment, recycled water can also be used to create or
enhance wetlands and riparian habitats. [WGII 10.5.2]
Effective adaptation and adaptive capacity, particularly in
developing Asian countries, will continue to be limited by
various ecological, social and economic, technical, institutional
and political constraints. Water recycling is a sustainable
approach towards adaptation to climate change and can be
cost-effective in the long term. However, the treatment of
wastewater for reuse that is now being practised in Singapore,
and the installation of distribution systems, can initially be
expensive compared to water supply alternatives such as the
use of imported water or groundwater. Nevertheless, they are
Section 5
Analysing regional aspects of climate change and water resources
Box 5.4: Tsho Rolpa Risk Reduction Project in Nepal as observed
anticipatory adaptation. [WGII Box 17.1]
The Tsho Rolpa is a glacial lake located at an altitude of about 4,580 m in Nepal. Glacier shrinkage increased the size of
the Tsho Rolpa from 0.23 km2 in 1957/58 to 1.65 km2 in 1997 (Figure 5.6). The 90–100 million m3 of water contained by
the lake at this time were only held back by a moraine dam – a hazard that required urgent action to reduce the risk of a
catastrophic glacial lake outburst flood (GLOF).
Figure 5.6: Changes in the area of the Tsho Rolpa over time.
If the dam were breached, one-third or more of the water could flood downstream. Among other considerations, this
posed a major risk to the Khimti hydropower plant, which was under construction downstream. These concerns spurred
the Government of Nepal, with the support of international donors, to initiate a project in 1998 to lower the level of the lake
through drainage. An expert group recommended that, to reduce the risk of a GLOF, the lake should be lowered three
metres by cutting a channel in the moraine. A gate was constructed to allow for controlled release of water. Meanwhile,
an early-warning system was established in nineteen villages downstream in case a Tsho Rolpa GLOF should occur
despite these efforts. Local villagers were actively involved in the design of the system, and safety drills are carried out
periodically. In 2002, the four-year construction project was completed at a cost of US$3.2 million. Clearly, reducing GLOF
risks involves substantial costs and is time-consuming, as complete prevention of a GLOF would require further drainage
to lower the lake level.
The case of Tsho Rolpa has to be seen in a broader context. The frequency of glacial lake outburst floods (GLOFs) in
the Himalayas of Nepal, Bhutan and Tibet has increased from 0.38 events/yr in the 1950s to 0.54 events/yr in the 1990s.
[WGII 1.3.1.1]
Sources: Mool et al. (2001), OECD (2003), Shrestha and Shrestha (2004).
89
Section 5
Analysing regional aspects of climate change and water resources
potentially important adaptation options in many countries of
Asia. Reduction of water wastage and leakage could be practised
in order to cushion decreases in water supply due to declines in
precipitation and increases in temperature. The use of marketoriented approaches to reduce wasteful water use could also be
effective in reducing adverse climate change impacts on water
resources. In rivers such as the Mekong, where wet-season
discharge is projected to increase and the dry-season flows
projected to decrease, planned water management interventions
such as dams and reservoirs could marginally decrease wetseason flows and substantially increase dry-season flows.
[WGII 10.5.2, 10.5.7]
5.3 Australia and New Zealand
5.3.1
Context
Although Australia and New Zealand are very different
hydrologically and geologically, both are already experiencing
water supply impacts from recent climate change, due to
natural variability and to human activity. The strongest regional
driver of natural climate variability is the El Niño–Southern
Oscillation cycle (Section 2.1.7). Since 2002, virtually all of
the eastern states and the south-west region of Australia have
moved into drought. This drought is at least comparable to
the so-called ‘Federation droughts’ of 1895 and 1902, and has
generated considerable debate about climate change and its
impact on water resources, and sustainable water management.
[WGII 11.2.1, 11.2.4]
Increases in water demand have placed stress on supply
capacity for irrigation, cities, industry and environmental
flows. Increased demand since the 1980s in New Zealand has
been due to agricultural intensification (Woods and HowardWilliams, 2004). The irrigated area of New Zealand has
increased by around 55% each decade since the 1960s (Lincoln
Environmental, 2000). From 1985 to 1996, Australian water
demand increased by 65% (NLWRA, 2001). In Australia,
dryland salinity, alteration of river flows, over-allocation
and inefficient use of water resources, land clearing, the
intensification of agriculture and fragmentation of ecosystems
are major sources of environmental stress (SOE, 2001; Cullen,
2002). In the context of projected climate change, water
supply is one of the most vulnerable sectors in Australia
and is expected to be a major issue in parts of New Zealand.
[WGII 11.ES, 11.2.4, 11.7]
5.3.2
Observed changes
The winter-rainfall-dominated region of south-west Western
Australia has experienced a substantial decline in the May–July
rainfall since the mid-20th century. The effects of the decline on
natural runoff have been severe, as evidenced by a 50% drop in
annual inflows to reservoirs supplying the city of Perth (Figure
5.7). Similar pressures have been imposed on local groundwater
resources and wetlands. This has been accompanied by a 20%
increase in domestic usage in 20 years, and a population growth
of 1.7% per year (IOCI, 2002). Although no formal attribution
studies were available at the time of the AR4, climate simulations
indicated that at least some of the observed drying was related
Figure 5.7: Annual inflow to Perth Water Supply System from 1911 to 2006. Horizontal lines show averages. Source:
http://www.watercorporation.com.au/D/dams_streamflow.cfm (courtesy of the Water Corporation of Western Australia).
[WGII Figure 11.3]
90
Analysing regional aspects of climate change and water resources
Section 5
to the enhanced greenhouse effect (IOCI, 2002). In recent years,
an intense multi-year drought has emerged in eastern and other
parts of southern Australia. For example, the total inflow to the
Murray River over the five years prior to 2006 was the lowest
five-year sequence on record. [WGII 11.6]
5.3.3
Projected changes
5.3.3.1
Water
Ongoing water security problems are very likely to increase
by 2030 in southern and eastern Australia, and parts of eastern
New Zealand that are distant from major rivers. [WGII 11.ES]
The Murray-Darling Basin is Australia’s largest river basin,
accounting for about 70% of irrigated crops and pastures
(MDBC, 2006). For the SRES A1 and B1 emission scenarios
and a wide range of GCMs, annual streamflow in the Basin is
projected to fall 10–25% by 2050 and 16–48% by 2100, with
salinity changes of −8 to +19% and −25 to +72%, respectively
(Beare and Heaney, 2002). [WGII Table 11.5] Runoff in twentynine Victorian catchments is projected to decline by 0–45%
(Jones and Durack, 2005). For the A2 scenario, projections
indicate a 6–8% decline in annual runoff in most of eastern
Australia, and 14% decline in south-west Australia, in the period
2021–2050 relative to 1961–1990 (Chiew et al., 2003). A risk
assessment for the city of Melbourne using ten climate models
(driven by the SRES B1, A1B and A1F scenarios) indicated
average streamflow declines of 3–11% by 2020 and 7–35% by
2050; however, planned demand-side and supply-side actions
may alleviate water shortages through to 2020 (Howe et al.,
2005). Little is known about future impacts on groundwater in
Australia. [WGII 11.4.1]
In New Zealand, proportionately more runoff is very likely from
South Island rivers in winter, and less in summer (Woods and
Howard-Williams, 2004). This is very likely to provide more
water for hydro-electric generation during the winter peak
demand period, and reduce dependence on hydro-storage lakes
to transfer generation capacity into the next winter. However,
industries dependent on irrigation (e.g., dairy, grain production,
horticulture) are likely to experience negative effects due to
lower water availability in spring and summer, their time of
peak demand. Increased drought frequency is very likely in
eastern areas, with potential losses in agricultural production
from unirrigated land (Mullan et al., 2005). The effects of
climate change on flood and drought frequency are virtually
certain to be modulated by phases of the ENSO and IPO
(McKerchar and Henderson, 2003). The groundwater aquifer
for Auckland City has spare capacity to accommodate recharge
under all the scenarios examined (Namjou et al., 2006). Base
flows in principal streams and springs are very unlikely to
be compromised unless many dry years occur in succession.
[WGII 11.4.1.1]
5.3.3.2
Energy
In Australia and New Zealand, climate change could affect
energy production in regions where climate-induced reductions
in water supplies lead to reductions in feed water for hydropower
turbines and cooling water for thermal power plants. In New
Zealand, increased westerly wind speed is very likely to
enhance wind generation and spillover precipitation into major
South Island hydro-catchments, and to increase winter rain in
the Waikato catchment (Ministry for the Environment, 2004).
Warming is virtually certain to increase melting of snow, the
ratio of rainfall to snowfall, and river flows in winter and early
spring. This is very likely to assist hydro-electric generation at
the time of peak energy demand for heating. [WGII 11.4.10]
5.3.3.3
Health
There are likely to be alterations in the geographical range and
seasonality of some mosquito-borne infectious diseases, e.g.,
Ross River disease, dengue and malaria. Fewer, but heavier,
rainfall events are likely to affect mosquito breeding and increase
the variability in annual rates of Ross River disease, particularly
in temperate and semi-arid areas (Woodruff et al., 2002, 2006).
Dengue is a substantial threat in Australia; the climate of the
far north already supports Aedes aegypti (the major mosquito
vector of the dengue virus), and outbreaks of dengue have
occurred with increasing frequency and magnitude in farnorthern Australia over the past decade. Malaria is unlikely to
establish unless there is a dramatic deterioration in the public
health response (McMichael et al., 2003). [WGII 11.4.11]
Eutrophication is a major water-quality problem (Davis, 1997;
SOE, 2001). Toxic algal blooms are likely to appear more
frequently and be present for longer due to climate change.
They can pose a threat to human health for both recreation and
consumptive water use, and can kill fish and livestock (Falconer,
1997). Simple, resource-neutral, adaptive management
strategies, such as flushing flows, can substantially reduce their
occurrence and duration in nutrient-rich, thermally stratified
water bodies (Viney et al., 2003). [WGII 11.4.1]
5.3.3.4
Agriculture
Large shifts in the geographical distribution of agriculture
and its services are very likely. Farming of marginal land in
drier regions is likely to become unsustainable due to water
shortages, new biosecurity hazards, environmental degradation
and social disruption. [WGII 11.7] Cropping and other
agricultural industries reliant on irrigation are likely to be
threatened where irrigation water availability is reduced. For
maize in New Zealand, a reduction in growth duration reduces
crop water requirements, providing closer synchronisation of
development with seasonal climatic conditions (Sorensen et al.,
2000). The distribution of viticulture in both countries is likely
to change depending upon suitability compared to high-yield
pasture and silviculture, and upon irrigation water availability
and cost (Hood et al., 2002; Miller and Veltman, 2004; Jenkins,
2006). [WGII 11.4.3]
5.3.3.5
Biodiversity
Impacts on the structure, function and species composition of
many natural ecosystems are likely to be significant by 2020,
and are virtually certain to exacerbate existing stresses such
as invasive species and habitat loss (e.g., for migratory birds),
increase the probability of species extinctions, degrade many
natural systems and cause a reduction in ecosystem services for
91
Section 5
Analysing regional aspects of climate change and water resources
water supply. The impact of climate change on water resources
will also interact with other stressors such as invasive species
and habitat fragmentation. Saltwater intrusion as a result of
sea-level rise, decreases in river flows, and increased drought
frequency are very likely to alter species composition of
freshwater habitats, with consequent impacts on estuarine and
coastal fisheries (Bunn and Arthington, 2002; Hall and Burns,
2002; Herron et al., 2002; Schallenberg et al., 2003). [WGII
11.ES, 11.4.2]
seawater desalination) (see Table 5.2) [WGII Table 11.2, 11.6],
both countries have taken notable steps in building adaptive
capacity by increasing support for research and knowledge,
expanding assessments of the risks of climate change for
decision makers, infusing climate change into policies and
plans, promoting awareness, and dealing more effectively with
climate issues. However, there remain environmental, economic,
informational, social, attitudinal and political barriers to the
implementation of adaptation. [WGII 11.5]
5.3.4
In urban catchments, storm and recycled water could be used
to augment supply, although existing institutional arrangements
and technical systems for water distribution constrain
implementation. Moreover, there is community resistance to
the use of recycled water for human consumption (e.g., in such
cities as Toowoomba in Queensland, and Goulburn in New South
Wales). Installation of rainwater tanks is another adaptation
response and is now actively pursued through incentive policies
and rebates. For rural activities, more flexible arrangements for
allocation are required, via the expansion of water markets,
where trading can increase water-use efficiency (Beare and
Heaney, 2002). Substantial progress is being made in this
Adaptation and vulnerability
Planned adaptation can greatly reduce vulnerability, and
opportunities lie in the inclusion of risks due to climate change
on the demand as well as the supply side (Allen Consulting
Group, 2005). In major cities such as Perth, Brisbane, Sydney,
Melbourne, Adelaide, Canberra and Auckland, concerns about
population pressures, ongoing drought in southern and eastern
Australia, and the impact of climate change are leading water
planners to consider a range of adaptation options. While some
adaptation has already occurred in response to observed climate
change (e.g., ongoing water restrictions, water recycling,
Table 5.2: Examples of government adaptation strategies to cope with water shortages in Australia. [WGII Table 11.2] Note that the
investment figures were accurate at the time the Fourth Assessment went to press in 2007, and do not reflect later developments.
Government
Strategy
Investment
Source
Australia
Drought aid payments to rural communities
US$0.7 billion from 2001 to 2006
DAFF, 2006b
Australia
National Water Initiative, supported by the
Australian Water Fund
US$1.5 billion from 2004 to 2009
DAFF, 2006a
Australia
Murray-Darling Basin Water Agreement
US$0.4 billion from 2004 to 2009
DPMC, 2004
Victoria
Melbourne’s Eastern Treatment Plant to
supply recycled water
US$225 million by 2012
Melbourne Water,
2006
Victoria
New pipeline from Bendigo to Ballarat, water
recycling, interconnections between dams,
reducing channel seepage, conservation
measures
US$153 million by 2015
Premier of Victoria,
2006
Victoria
Wimmera Mallee pipeline replacing open
irrigation channels
US$376 million by 2010
Vic DSE, 2006
NSW
NSW Water Savings Fund supports projects
which save or recycle water in Sydney
US$98 million for Round 3, plus more than
US$25 million to 68 other projects
DEUS, 2006
Queensland (Qld)
Qld Water Plan 2005 to 2010 to improve
water-use efficiency and quality, recycling,
drought preparedness, new water pricing
Includes US$182 million for water infrastructure
in south-east Qld, and US$302 million to other
infrastructure programmes
Queensland
Government, 2005
South Australia
Water Proofing Adelaide project is a blueprint
for the management, conservation and
development of Adelaide’s water resources
to 2025
N/A
Government of South
Australia, 2005
Western
Australia (WA)
State Water Strategy (2003) and State Water
Plan (proposed)
WA Water Corporation doubled supply from
1996 to 2006
US$500 million spent by WA Water Corporation
from 1996 to 2006, plus US$290 million for the
Perth desalination plant
Government of
Western Australia,
2003, 2006; Water
Corporation, 2006
92
Analysing regional aspects of climate change and water resources
Section 5
regard. Under the National Water Initiative, states, territories
and the Australian Government are now committed to pursuing
best-practice water pricing and institutional arrangements to
achieve consistency in water charging. [WGII 11.5]
When climate change impacts are combined with other
non-climate trends, there are some serious implications for
sustainability in both Australia and New Zealand. In some river
catchments, where increasing urban and rural water demand
has already exceeded sustainable levels of supply, ongoing and
proposed adaptation strategies [WGII 11.2.5] are likely to buy
some time. Continued rates of coastal development are likely
to require tighter planning and regulation if such developments
are to remain sustainable. [WGII 11.7]
5.4 Europe
5.4.1
Context
Europe is well watered, with numerous permanent rivers, many
of which flow outward from the central part of the continent.
It also has large areas with low relief. The main types of
climate in Europe are maritime, transitional, continental, polar
and Mediterranean; the major vegetation types are tundra,
coniferous taiga (boreal forest), deciduous-mixed forest,
steppe and Mediterranean. A relatively large proportion of
Europe is farmed, with about one-third of the area being
classified as arable and cereals being the predominant crop.
[WGII TAR 13.1.2.1]
The sensitivity of Europe to climate change has a distinct north–
south gradient, with many studies indicating that southern
Europe will be the more severely affected (EEA, 2004).
The already hot and semi-arid climate of southern Europe
is expected to become still warmer and drier, threatening its
waterways, hydropower, agricultural production and timber
harvests. In central and eastern Europe, summer precipitation
is projected to decrease, causing higher water stress. Northern
countries are also vulnerable to climate change, although in
the initial stages of warming there may be some benefits in
terms of, for example, increased crop yields and forest growth.
[WGII 12.2.3, SPM]
Key environmental pressures relate to biodiversity, landscape,
soil and land degradation, forest degradation, natural hazards,
water management, and recreational environments. Most
ecosystems in Europe are managed or semi-managed; they are
often fragmented and under stress from pollution and other
human impacts. [WGII TAR 13.1.2.1]
5.4.2
Observed changes
Mean winter precipitation increased over the period 1946–1999
across most of Atlantic- and northern Europe (Klein Tank et al.,
2002) and this has to be interpreted, in part, in the context of
winter NAO changes (Scaife et al., 2005). In the Mediterranean
area, yearly precipitation trends over the period 1950–2000 were
negative in the eastern part (Norrant and Douguédroit, 2006).
An increase in mean precipitation per wet day is observed in
most parts of the continent, even in some areas which are getting
drier (Frich et al., 2002; Klein Tank et al., 2002; Alexander et al.,
2006). As a result of these and other changes in the hydrological
and thermal regimes (cf. Auer et al., 2007), observed impacts
have been documented in other sectors, and some of these are
set out in Table 5.3. [WGI Chapter 3; WGII 12.2.1]
5.4.3
Projected changes
5.4.3.1
Water
Generally, for all scenarios, projected mean annual precipitation
increases in northern Europe and decreases further south.
However, the change in precipitation varies substantially from
season to season and across regions in response to changes in
large-scale circulation and water vapour loading. Räisänen et
al. (2004) project that summer precipitation would decrease
Table 5.3: Attribution of recent changes in natural and managed ecosystems to recent temperature and precipitation trends.
[Selected from WGII Table 12.1]
Region
Observed change
Reference
Disappearance of some types of wetlands (palsa mires)
in Lapland; increased species richness and frequency at
altitudinal margin of plant life
Klanderud and Birks, 2003; Luoto et al.,
2004
Parts of northern
Europe
Cryosphere
Increased crop stress during hotter drier summers; increased
risk to crops from hail
Viner et al., 2006
Russia
Decrease in thickness and areal extent of permafrost and
damages to infrastructure
Decrease in seasonal snow cover (at lower elevations)
Frauenfeld et al., 2004; Mazhitova et al.,
2004
Laternser and Schneebeli, 2003; Martin and
Etchevers, 2005
Hoelzle et al., 2003
Terrestrial ecosystems
Fennoscandian mountains
and sub-Arctic
Agriculture
Alps
Europe
Decrease in glacier volume and area (except some glaciers in
Norway)
93
Section 5
Analysing regional aspects of climate change and water resources
substantially (in some areas up to 70% in the SRES A2 scenario) in
southern and central Europe, and to a smaller degree up to central
Scandinavia. Giorgi et al. (2004) identified enhanced anticyclonic
circulation in summer over the north-eastern Atlantic, which
induces a ridge over western Europe and a trough over eastern
Europe. This blocking structure deflects storms northward,
causing a substantial and widespread decrease of precipitation
(up to 30–45%) over the Mediterranean Basin as well as western
and central Europe. [WGI Table 11.1; WGII 12.3.1.1]
It is projected that climate change will have a range of impacts on
water resources (Table 5.3). Annual runoff increases are projected
in Atlantic- and northern Europe (Werritty, 2001; Andréasson et
al., 2004), and decreases in central, Mediterranean and eastern
Europe (Chang et al., 2002; Etchevers et al., 2002; Menzel and
Bürger, 2002; Iglesias et al., 2005). Annual average runoff is
projected to increase in northern Europe (north of 47°N) by
approximately 5–15% up to the 2020s and by 9–22% up to the
2070s, for the A2 and B2 scenarios and climate scenarios from
two different climate models (Alcamo et al., 2007). Meanwhile,
in southern Europe (south of 47°N), runoff is projected to
decrease by 0–23% up to the 2020s and by 6–36% up to the
2070s (for the same set of assumptions). Groundwater recharge
is likely to be reduced in central and eastern Europe (Eitzinger
et al., 2003), with a larger reduction in valleys (Krüger et al.,
2002) and lowlands, e.g., in the Hungarian steppes: (Somlyódy,
2002). [WGII 12.4.1, Figure 12.1]
Flow seasonality increases, with higher flows in the peak flow
season and either lower flows during the low-flow season or
extended dry periods (Arnell, 2003, 2004). [WGII 3.4.1] Studies
show an increase in winter flows and decrease in summer flows
in the Rhine (Middelkoop and Kwadijk, 2001), Slovakian rivers
(Szolgay et al., 2004), the Volga, and central and eastern Europe
(Oltchev et al., 2002). Initially, glacier retreat is projected to
enhance the summer flow in the rivers of the Alps. However,
when glaciers shrink, summer flow is projected to be reduced
(Hock et al., 2005) by up to 50% (Zierl and Bugmann, 2005).
Summer low flow is projected to decrease by up to 50% in
central Europe (Eckhardt and Ulbrich, 2003), and by up to
80% in some rivers in southern Europe (Santos et al., 2002).
[WGII 12.4.1]
The regions most prone to an increase in drought risk are the
Mediterranean and some parts of central and eastern Europe,
where the highest increase in irrigation water demand is
projected (Döll, 2002; Donevska and Dodeva, 2004). This
calls for developing sustainable land-use planning. Irrigation
requirements are likely to become substantial in countries (e.g.,
in Ireland) where it now hardly exists (Holden et al., 2003).
It is likely that, due to both climate change and increasing
water withdrawals, the area affected by severe water stress
(withdrawal/availability higher than 40%) will increase and
lead to increasing competition for available water resources
(Alcamo et al., 2003b; Schröter et al., 2005). [WGII 12.4.1]
Future risk of floods and droughts (see Table 5.4). Flood risk
is projected to increase throughout the continent. The regions
most prone to a rise in flood frequencies are eastern Europe,
then northern Europe, the Atlantic coast and central Europe,
while projections for southern and south-eastern Europe show
significant increases in drought frequencies. In some regions,
both the risks of floods and droughts are projected to increase
simultaneously. [WGII Table 12.4]
Christensen and Christensen (2003), Giorgi et al. (2004),
Kjellström (2004) and Kundzewicz et al. (2006) all found a
substantial increase in the intensity of daily precipitation events.
This holds even for areas with a decrease in mean precipitation,
such as central Europe and the Mediterranean. The impact of
this change over the Mediterranean region during summer is
not clear due to the strong convective rainfall component and its
great spatial variability (Llasat, 2001). [WGII 12.3.1.2]
The combined effects of higher temperatures and reduced
mean summer precipitation would enhance the occurrence of
Table 5.4: Impact of climate change on drought and flood occurrence in Europe for various time slices and under various
scenarios based on the ECHAM4 and HadCM3 models. [WGII Table 12.2]
Time slice
Water availability and droughts
Floods
2020s
Increase in annual runoff in northern Europe by up to 15% and
decrease in the South by up to 23%a
Increasing risk of winter flood in northern Europe and of flash
flood in all of Europe
Decrease in summer flowd
Risk of snowmelt flood shifts from spring to winterc
2050s
Decrease in annual runoff by up to 20–30% in south-eastern
Europeb
2070s
Increase in annual runoff in the North by up to 30% and decrease
by up to 36% in the Southa
Decrease in summer low flow by up to 80%b, d
Decreasing drought risk in N. Europe, increasing drought risk in
W. and S. Europe. By the 2070s, today’s 100-year droughts are
projected to return, on average, every 10 (or fewer) years in parts
of Spain and Portugal, western France, the Vistula Basin in Poland,
and western Turkeyc
a Alcamo et al., 2007; b Arnell, 2004, c Lehner et al., 2006, d Santos et al., 2002.
94
Today’s 100-year floods are projected to occur more frequently
in northern and north-eastern Europe (Sweden, Finland, N.
Russia), in Ireland, in central and E. Europe (Poland, Alpine
rivers), in Atlantic parts of S. Europe (Spain, Portugal); less
frequently in large parts of S. Europec
Section 5
Analysing regional aspects of climate change and water resources
heatwaves and droughts. Schär et al. (2004) conclude that the
future European summer climate would experience a pronounced
increase in year-to-year variability and thus a higher incidence
of heatwaves and droughts. The Mediterranean and even much
of eastern Europe may experience an increase in dry periods by
the late 21st century (Polemio and Casarano, 2004). According
to Good et al. (2006), the longest yearly dry spell would increase
by as much as 50%, especially over France and central Europe.
However, there is some recent evidence (Lenderink et al., 2007)
that some of these projections for droughts and heatwaves
may be slightly overestimated due to the parameterisation of
soil moisture in regional climate models. Decreased summer
precipitation in southern Europe, accompanied by rising
temperatures, which enhances evaporative demand, would
inevitably lead to reduced summer soil moisture (cf. Douville
et al., 2002) and more frequent and more intense droughts.
[WGII 3.4.3, 12.3.1]
Studies indicate a decrease in peak snowmelt floods by the
2080s in parts of the UK (Kay et al., 2006b), but the impact
of climate change on flood regime can be both positive or
negative, highlighting the uncertainty still remaining in climate
change impacts (Reynard et al., 2004). Palmer and Räisänen
(2002) analysed the modelled differences in winter precipitation
between the control run and an ensemble with transient increase
in CO2 and calculated around the time of CO2 doubling. Over
Europe, a considerable increase in the risk of a very wet winter
was found. The probability of total boreal winter precipitation
exceeding two standard deviations above normal was found to
increase considerably (even five- to seven-fold) over large areas
of Europe, with likely consequences on winter flood hazard.
[WGII 3.4.3]
5.4.3.2
Energy
Hydropower is a key renewable energy source in Europe
(19.8% of the electricity generated). By the 2070s, hydropower
potential for the whole of Europe is expected to decline by 6%,
translated into a 20–50% decrease around the Mediterranean, a
15–30% increase in northern and eastern Europe, and a stable
hydropower pattern for western and central Europe (Lehner
et al., 2005). Biofuel production is largely determined by the
supply of moisture and the length of the growing season (Olesen
and Bindi, 2002). [WGII 12.4.8.1]
5.4.3.3
Health
Climate change is also likely to affect water quality and quantity
in Europe, and hence the risk of contamination of public and
private water supplies (Miettinen et al., 2001; Hunter, 2003;
Elpiner, 2004; Kovats and Tirado, 2006). Both extreme rainfall
and droughts can increase the total microbial loads in freshwater
and have implications for disease outbreaks and water-quality
monitoring (Howe et al., 2002; Kistemann et al., 2002; Opopol
et al. 2003; Knight et al., 2004; Schijven and de Roda Husman,
2005). [WGII 12.4.11]
5.4.3.4
Agriculture
The predicted increase in extreme weather events (e.g., spells of
high temperature and droughts) (Meehl and Tebaldi, 2004; Schär
et al., 2004; Beniston et al., 2007) is projected to increase yield
variability (Jones et al., 2003b) and to reduce average yield (Trnka
et al., 2004). In particular, in the European Mediterranean region,
increases in the frequency of extreme climate events during
specific crop development stages (e.g., heat stress during the
flowering period, rainy days during sowing dates), together with
higher rainfall intensity and longer dry spells, is likely to reduce
the yield of summer crops (e.g., sunflower). [WGII 12.4.7.1]
5.4.3.5
Biodiversity
Many systems, such as the permafrost areas in the Arctic
and ephemeral (short-lived) aquatic ecosystems in the
Mediterranean, are projected to disappear. [WGII 12.4.3]
Loss of permafrost in the Arctic (ACIA, 2004) will be likely
to cause a reduction in some types of wetlands in the current
permafrost zone (Ivanov and Maximov, 2003). A consequence
of warming could be a higher risk of algal blooms and increased
growth of toxic cyanobacteria in lakes (Moss et al., 2003; Straile
et al., 2003; Briers et al., 2004; Eisenreich, 2005). Higher
precipitation and reduced frost may enhance nutrient loss from
cultivated fields and result in higher nutrient loadings (Bouraoui
et al., 2004; Kaste et al., 2004; Eisenreich, 2005), leading to
intensive eutrophication of lakes and wetlands (Jeppesen et al.,
2003). Higher temperatures will also reduce dissolved oxygen
saturation levels and increase the risk of oxygen depletion
(Sand-Jensen and Pedersen, 2005). [WGII 12.4.5]
Higher temperatures are likely to lead to increased species
richness in freshwater ecosystems in northern Europe and
decreases in parts of south-western Europe (Gutiérrez Teira,
2003). [WGII 12.4.6]
5.4.4
Adaptation and vulnerability
Climate change will pose two major water management
challenges in Europe: increasing water stress mainly in southeastern Europe, and increasing risk of floods throughout most of
the continent. Adaptation options to cope with these challenges
are well documented (IPCC, 2001b). Reservoirs and dykes are
likely to remain the main structural measures to protect against
floods in highland and lowland areas, respectively (Hooijer
et al., 2004). However, other planned adaptation options are
becoming more popular, such as expanded floodplain areas
(Helms et al., 2002), emergency flood reservoirs (Somlyódy,
2002), preserved areas for flood water (Silander et al., 2006),
and flood forecasting and warning systems, especially for flash
floods. Multi-purpose reservoirs serve as an adaptation measure
for both floods and droughts. [WGII 12.5.1]
To adapt to increasing water stress, the most common and
planned strategies remain supply-side measures such as
impounding rivers to form instream reservoirs (Santos et al.,
2002; Iglesias et al., 2005). However, new reservoir construction
is being increasingly constrained in Europe by environmental
regulations (Barreira, 2004) and high investment costs (Schröter
et al., 2005). Other supply-side approaches, such as wastewater
reuse and desalination, are being more widely considered, but
95
Analysing regional aspects of climate change and water resources
their popularity is dampened, respectively, by health concerns
in using wastewater (Geres, 2004), and the high energy costs of
desalination (Iglesias et al., 2005). Some planned demand-side
strategies are also feasible (AEMA, 2002), such as household,
industrial and agricultural water conservation, reducing leaky
municipal and irrigation water systems (Donevska and Dodeva,
2004; Geres, 2004), and water pricing (Iglesias et al., 2005).
Irrigation water demand may be reduced by introducing crops
that are more suited to a changing climate. An example of a
unique European approach to adapting to water stress is that
regional- and watershed-level strategies to adapt to climate
change are being incorporated into plans for integrated water
management (Kabat et al., 2002; Cosgrove et al., 2004;
Kashyap, 2004), while national strategies are being designed to
fit into existing governance structures (Donevska and Dodeva,
2004). [WGII 12.5.1]
•
•
Adaptation procedures and risk management practices for
the water sector are being developed in some countries and
regions (e.g., the Netherlands, the UK and Germany) that
recognise the uncertainty of projected hydrological changes.
[WGII 3.ES, 3.2, 3.6]
5.5 Latin America
5.5.1
Context
Population growth continues, with consequences for food
demand. Because the economies of most Latin American
countries depend on agricultural productivity, regional variation
in crop yields is a very relevant issue. Latin America has a large
variety of climate as result of its geographical configuration.
The region also has large arid and semi-arid areas. The climatic
spectrum ranges from cold, icy high elevations to temperate
and tropical climate. Glaciers have generally receded in
the past decades, and some very small glaciers have already
disappeared.
The Amazon, the Parana-Plata and Orinoco together carry into
the Atlantic Ocean more than 30% of the renewable freshwater of
the world. However, these water resources are poorly distributed,
and extensive zones have very limited water availability (Mata
et al., 2001). There are stresses on water availability and quality
where low precipitation or higher temperatures occur. Droughts
that are statistically linked to ENSO events generate rigorous
restrictions on the water resources of many areas in Latin
America.
5.5.2
Observed changes
5.5.2.1
Water
Over the past three decades, Latin America has been subject
to climate-related impacts, some of them linked with ENSO
events.
•
Increases in climate extremes such as floods, droughts and
landslides (e.g., heavy precipitation in Venezuela (1999
and 2005); the flooding in the Argentinean Pampas (2000
96
•
•
Section 5
and 2002), the Amazon drought (2005), destructive hail
storms in Bolivia (2002) and in Buenos Aires (2006),
Cyclone Catarina in the South Atlantic (2004), and the
record hurricane season of 2005 in the Caribbean region).
The occurrence of climate-related disasters increased by
2.4 times between the periods 1970–1999 and 2000–2005,
continuing the trend observed during the 1990s. Only
19% of the events between 2000 and 2005 have been
economically quantified, representing losses of nearly
US$20 billion (Nagy et al., 2006). [WGII 13.2.2]
Stress on water availability: droughts related to La Niña
created severe restrictions for the water supply and
irrigation demands in central western Argentina and in
central Chile. Droughts related to El Niño reduced the flow
of the Cauca River in Colombia. [WGII 13.2.2]
Increases in precipitation were observed in southern Brazil,
Paraguay, Uruguay, north-east Argentina (Pampas), and
parts of Bolivia, north-west Peru, Ecuador and north-west
Mexico. The higher precipitation provoked a 10% increase
in flood frequency in the Amazon River at Obidos; a 50%
increase in streamflow in the rivers of Uruguay, Parana
and Paraguay; and more floods in the Mamore Basin in
Bolivian Amazonia. An increase in intense rainfall events
and consecutive dry days was also observed over the
region. Conversely, a declining trend in precipitation was
observed in Chile, south-western Argentina, north-eastern
Brazil, southern Peru and western Central America (e.g.,
Nicaragua). [WGII 13.2.4.1]
A sea-level rise rate of 2–3 mm/yr during the last 10–
20 years in south-eastern South America. [WGII 13.2.4.1]
Glaciers in the tropical Andes of Bolivia, Peru, Ecuador
and Colombia have decreased in area by amounts similar
to global changes since the end of the Little Ice Age (see
Figure 5.9). The smallest glaciers have been affected the
most (see Box 5.5). The reasons for these changes are
not the same as those in mid- and high latitudes, being
related to complex and spatially varying combinations of
higher temperatures and changes in atmospheric moisture
content. [WGI 4.5.3]
Further indications of observed trends in hydrological variables
are given in Table 5.5 and Figure 5.8.
5.5.2.2
Energy
Hydropower is the main electrical energy source for most
countries in Latin America, and is vulnerable to large-scale
and persistent rainfall anomalies due to El Niño and La
Niña, as observed in Argentina, Colombia, Brazil, Chile,
Peru, Uruguay and Venezuela. A combination of increased
energy demand and droughts caused a virtual breakdown of
hydro-electricity in most of Brazil in 2001 and contributed
to a reduction in GDP (Kane, 2002). Glacier retreat is also
affecting hydropower generation, as observed in the cities of
La Paz and Lima. [WGII 13.2.2, 13.2.4]
5.5.2.3
Health
There are linkages between climate-related extreme events
and health in Latin America. Droughts favour epidemics in
Analysing regional aspects of climate change and water resources
Section 5
Table 5.5: Some recent trends in hydrological variables. [WGII Table 13.1, Table 13.2, Table 13.3]
Current trends in precipitation (WGII Table 13.2)
Precipitation (change shown in % unless otherwise indicated)
Period
Change
Amazonia – northern/southern (Marengo, 2004)
1949–1999
Bolivian Amazonia (Ronchail et al., 2005)
since 1970
-11 to -17 / -23 to
+18
+15
Argentina – central and north-east (Penalba and Vargas, 2004)
1900–2000
+1 SD to +2 SD
Uruguay (Bidegain et al., 2005)
1961–2002
+ 20
Chile – central (Camilloni, 2005)
last 50 years
-50
1961–1990
-4 to +6
Colombia (Pabón, 2003)
Selected hydrological extremes and their impacts, 2004–2006 (WGII Table 13.1)
Heavy rains
Sep. 2005
Colombia: 70 deaths, 86 injured, 6 disappeared and 140,000 flood victims
(NOAA, 2005).
Heavy rains
Feb. 2005
Venezuela: heavy precipitation (mainly on central coast and in Andean mountains), severe floods and heavy landslides.
Losses of US$52 million; 63 deaths and 175,000 injuries (UCV, 2005; DNPC, 2005/2006).
Droughts
2004–2006
Argentina – Chaco: losses estimated at US$360 million; 120,000 cattle lost, 10,000 evacuees in 2004 (SRA, 2005). Also
in Bolivia and Paraguay: 2004/05.
Brazil – Amazonia: severe drought affected central and south-western Amazonia, probably associated with warm sea
surface temperatures in the tropical North Atlantic (http://www.cptec.inpe.br/).
Brazil – Rio Grande do Sul: reductions of 65% and 56% in soybean and maize production (http://www.ibge.gov.br/home/
In English: http://www.ibge.gov.br/english/).
Glacier retreat trends (WGII Table 13.3)
Glaciers/Period
Changes/Impacts
Peru
last 35 years
22% reduction in glacier total area (cf. Figure 5.9); reduction of 12% in freshwater in the coastal zone (where 60% of the
country’s population live). Estimated water loss almost 7,000 × 106 m3
Peruc
last 30 years
Reduction up to 80% of glacier surface from very small glaciers; loss of 188 × 106 m 3 in water reserves during the last
50 years.
Colombiad
1990–2000
82% reduction in glaciers; under the current climate trends, Colombia’s glaciers are expected to disappear completely
within the next 100 years.
Ecuadore
1956–1998
There has been a gradual decline in glacier length; reduction of water supply for irrigation, clean water supply for the city
of Quito.
Boliviaf
since mid-1990s
Projected glacier shrinkage in Bolivia indicates adverse consequences for water supply and hydropower generation for
the city of La Paz. Also see Box 5.5.
a,b
Vásquez, 2004; b Mark and Seltzer, 2003; c NC-Perú, 2001; d NC-Colombia, 2001; e NC-Ecuador, 2000; f Francou et al., 2003.
a Colombia and Guyana, while floods engender epidemics in the
dry northern coastal region of Peru (Gagnon et al., 2002). Annual
variations in dengue/dengue haemorrhagic fever in Honduras
and Nicaragua appear to be related to climate-driven fluctuations
in vector densities (temperature, humidity, solar radiation
and rainfall) (Patz et al., 2005). Flooding produced outbreaks
of leptospirosis in Brazil, particularly in densely populated
areas without adequate drainage (Ko et al., 1999; Kupek et al.,
2000). The distribution of schistosomiasis is probably linked to
climatic factors. Concerning diseases transmitted by rodents,
there is good evidence that some increases in occurrence are
observed during/after heavy rainfall and flooding because of
altered patterns of human–pathogen–rodent contact. In some
coastal areas of the Gulf of Mexico, an increase in sea surface
temperature and precipitation has been associated with an
increase in dengue transmission cycles (Hurtado-Díaz et al.,
2006). [WGII 13.2.2, 8.2.8.3]
5.5.2.4
Agriculture
As a result of high rainfall and humidity caused by El Niño,
several fungal diseases in maize, potato, wheat and bean are
observed in Peru. Some positive impacts are reported for the
Argentinean Pampas region, where increases in precipitation
led to increases in crop yields close to 38% in soybean, 18%
in maize, 13% in wheat, and 12% in sunflower. In the same
way, pasture productivity increased by 7% in Argentina and
Uruguay. [WGII 13.2.2, 13.2.4]
5.5.2.5
Biodiversity
There are few studies assessing the effects of climate change on
biodiversity, and in all of them it is difficult to differentiate the
effects caused by climate change from those arising from other
factors. Tropical forests of Latin America, particularly those of
Amazonia, are increasingly susceptible to fire occurrences due
to increased El Niño-related droughts and to land-use change
97
Analysing regional aspects of climate change and water resources
Section 5
Figure 5.8: Trends in annual rainfall in (a) South America (1960–2000). An increase is shown by a plus sign, a decrease
by a circle; bold values indicate significance at P ≤ 0.05 (reproduced from Haylock et al. (2006) with permission from
the American Meteorological Society). (b) Central America and northern South America (1961–2003). Large red triangles
indicate positive significant trends, small red triangles indicate positive non-significant trends, large blue triangles indicate
negative significant trends, and small blue triangles indicate negative non-significant trends (reproduced from Aguilar et al.
(2005) with permission from the American Geophysical Union. [WGII Figure 13.1]
(deforestation, selective logging and forest fragmentation).
[WGII 13.2.2]
In relation to biodiversity, populations of toads and frogs
in cloud forests were found to be affected after years of low
precipitation. In Central and South America, links between
higher temperatures and frog extinctions caused by a skin
disease (Batrachochytrium dendrobatidis) were found. One
study considering data from 1977–2001 showed that coral
cover on Caribbean reefs decreased by 17% on average in the
year following a hurricane, with no evidence of recovery for at
least eight post-impact years. [WGII 13.2.2]
5.5.3
Projected changes
5.5.3.1
Water and climate
With medium confidence, the projected mean warming for Latin
America for 2100, according to different climate models, ranges
from 1ºC to 4ºC for the B2 emissions scenario and from 2ºC to
6ºC for the A2 scenario. Most GCM projections indicate larger
(positive or negative) rainfall anomalies for the tropical region
and smaller ones for the extra-tropical part of South America.
In addition, extreme dry seasons are projected to become more
frequent in Central America, for all seasons. Beyond these
results there is relatively little agreement between models on
changes in the frequency of extreme seasons for precipitation.
For daily precipitation extremes, one study based on two
AOGCMs suggests an increase in the number of wet days over
parts of south-eastern South America and central Amazonia,
and weaker daily precipitation extremes over the coast of northeast Brazil. [WGI Table 11.1, 11.6; WGII 13.ES, 13.3.1]
98
The number of people living in already water-stressed
watersheds (i.e., having supplies less than 1,000 m3/capita/yr)
in the absence of climate change is estimated at 22.2 million
(in 1995). Under the SRES scenarios, this number is estimated
to increase to between 12 and 81 million in the 2020s and to
between 79 and 178 million in the 2050s (Arnell, 2004). These
estimates do not take into account the number of people moving
out of water stress, which is shown in Table 5.6. The current
vulnerabilities observed in many regions of Latin American
countries will be increased by the joint negative effect of
growing demands due to an increasing population rate for
water supply and irrigation, and the expected drier conditions
in many basins. Therefore, taking into account the number of
people experiencing decreased water stress, there is still a net
increase in the number of people becoming water-stressed.
[WGII 13.4.3]
5.5.3.2 Energy
Expected further glacier retreat is projected to impact the
generation of hydro-electricity in countries such as Colombia
and Peru (UNMSM, 2004). Some small tropical glaciers have
already disappeared, and others are likely to do so within
the next few decades, with potential effects on hydropower
generation (Ramírez et al., 2001). [WGI 4.5.3; WGII 13.2.4]
5.5.3.3 Health
Around 262 million people, representing 31% of the Latin
American population, live in malaria risk areas (i.e., tropical and
sub-tropical regions) (PAHO, 2003). Based on SRES emissions
scenarios and socio-economic scenarios, some projections
indicate decreases in the length of the transmission season of
Section 5
Analysing regional aspects of climate change and water resources
Box 5.5: Changes in South American glaciers. [WGII Box 1.1]
A general glacier shrinkage in the tropical Andes has been observed and, as in other mountain ranges, the smallest
glaciers are more strongly affected [WGI 4.5.3], with many of them having already disappeared during the last century. As
for the largely glacier-covered mountain ranges such as the Cordillera Blanca in Peru and the Cordillera Real in Bolivia,
total glacier area has shrunk by about one-third of the Little Ice Age extent (Figure 5.9).
Figure 5.9: Extent (%) of the total surface area of
glaciers of the tropical Cordillera Blanca, Peru,
relative to their extent around 1925 (=100) (Georges,
2004). The area of glacier in the Cordillera Blanca in
1990 was 620 km2. [Extracted from WGI Figure 4.16]
The Chacaltaya Glacier in Bolivia (16°S) is a typical example of a disintegrating, and most probably disappearing, small
glacier. Its area in 1940 was 0.22 km2, and this has currently (in 2005) reduced to less than 0.01 km2 (Figure 5.10) (Ramírez
et al., 2001; Francou et al., 2003; Berger et al., 2005). Over the period 1992 to 2005, the glacier suffered a loss of 90% of
its surface area, and 97% of its volume of ice (Berger et al., 2005). A linear extrapolation from these observed numbers
indicates that it may disappear completely before 2010 (Coudrain et al., 2005). Although, in the tropics, glacier mass balance
responds sensitively to changes in precipitation and humidity [WGI 4.5.3], the shrinkage of Chacaltaya is consistent with an
ascent of the 0°C isotherm of about 50 m/decade in the tropical Andes since the 1980s (Vuille et al., 2003).
With a mean altitude of 5,260 m above sea level, the glacier was the highest skiing station in the world until a few years
ago. The ongoing shrinkage of the glacier during the 1990s has led to its near disappearance, and as a consequence
Bolivia has lost its only ski resort (Figure 5.10).
Figure 5.10: Areal extent of Chacaltaya Glacier, Bolivia, from 1940 to 2005. By 2005, the glacier had separated into
three distinct small bodies. The position of the ski hut, which did not exist in 1940, is indicated with a red cross. The ski
lift had a length of about 800 m in 1940 and about 600 m in 1996 (shown by a continuous line in 1940 and a broken line
in all other panels) and was normally installed during the precipitation season. After 2004, skiing was no longer possible.
Photo credits: Francou and Vincent (2006) and Jordan (1991). [WGII Figure 1.1]
99
Section 5
Analysing regional aspects of climate change and water resources
Table 5.6: Increase in the numbers of people living in waterstressed watersheds in Latin America (million) based on the
HadCM3 GCM (Arnell, 2004). [WGII Table 13.6]
Scenario
and GCM
1995
2025
2055
Without
climate
change
With
climate
change
Without
climate
change
With
climate
change
A1
22.2
35.7
21.0
54.0
60.0
A2
22.2
55.9
37.0–66.0
149.3
60.0–150.0
B1
22.2
35.7
22.0
54.0
74.0
B2
22.2
47.3
7.0–77.0
59.4
62.0
malaria in many areas where reductions in precipitation are
projected, such as the Amazon and Central America. The results
report additional numbers of people at risk in areas around the
southern limit of the disease distribution in South America (van
Lieshout et al., 2004). Nicaragua and Bolivia have predicted a
possible increase in the incidence of malaria in 2010, reporting
seasonal variations (Aparicio, 2000; NC-Nicaragua, 2001).
The increase in malaria and population at risk could affect the
costs of health services, including treatment and social security
payments. [WGII 13.4.5]
Other models project a substantial increase in the number of
people at risk of dengue due to changes in the geographical
limits of transmission in Mexico, Brazil, Peru and Ecuador
(Hales et al., 2002). Some models project changes in the spatial
distribution (dispersion) of the cutaneous leishmaniasis vector
in Peru, Brazil, Paraguay, Uruguay, Argentina and Bolivia
(Aparicio, 2000; Peterson and Shaw, 2003), as well as the
monthly distribution of the dengue vector (Peterson et al.,
2005). [WGII 13.4.5]
5.5.3.4
Agriculture
Several studies using crop simulation models, under climate
change, for commercial crops, were run for the Latin America
region. The number of people at risk of hunger under SRES
emissions scenario A2 is projected to increase by 1 million
in 2020, while it is projected that there will be no change for
2050 and that the number will decrease by 4 million in 2080.
[WGII Table 13.5, 13.4.2]
5.5.3.5
Biodiversity
Through a complex set of alterations comprising a modification
in rainfall and runoff, a replacement of tropical forest by
savannas is expected in eastern Amazonia and the tropical
forests of central and southern Mexico, along with replacement
of semi-arid by arid vegetation in parts of north-east Brazil
and most of central and northern Mexico due to the synergistic
effects of both land-use and climate changes. By the 2050s,
50% of agricultural lands are very likely to be subjected to
desertification and salinisation in some areas. [WGII 13.ES,
13.4.1, 13.4.2]
100
5.5.4
Adaptation and vulnerability
5.5.4.1
Past and current adaptation
The lack of adequate adaptation strategies to cope with the hazards
and risks of floods and droughts in Latin American countries
is due to low gross national product (GNP), the increasing
population settling in vulnerable areas (prone to flooding,
landslides or drought), and the absence of the appropriate
political, institutional and technological frameworks (Solanes
and Jouravlev, 2006). Nevertheless, some communities and
cities have organised themselves, becoming active in disaster
prevention (Fay et al., 2003b). Many poor inhabitants have been
encouraged to relocate from flood-prone areas to safer places.
With the assistance of IRDB and IDFB loans, they built new
homes, e.g., resettlements in the Paraná River Basin of Argentina,
after the 1992 flood (IRDB, 2000). In some cases, a change in
environmental conditions affecting the typical economy of the
Pampas has led to the introduction of new production activities
through aquaculture, using natural regional fish species such as
pejerrey (Odontesthes bonariensis) (La Nación, 2002). Another
example, in this case related to the adaptive capacity of people
to water stresses, is provided by ‘self-organisation’ programmes
for improving water supply systems in very poor communities.
The organisation Business Partners for Development Water
and Sanitation Clusters has been working on four ‘focus’ plans
in Latin America: Cartagena (Colombia), La Paz and El Alto
(Bolivia), and some underprivileged districts of Gran Buenos
Aires (Argentina) (The Water Page, 2001; Water 21, 2002).
Rainwater cropping and storage systems are important features
of sustainable development in the semi-arid tropics. In particular,
there is a joint project developed in Brazil by the NGO Network
Articulação no Semi-Árido (ASA) Project, called the P1MC
Project, for one million cisterns to be installed by civilian
society in a decentralised manner. The plan is to supply drinking
water to one million rural households in the perennial drought
areas of the Brazilian semi-arid tropics (BSATs). During the
first stage, 12,400 cisterns were built by ASA and the Ministry
of Environment of Brazil and a further 21,000 were planned
by the end of 2004 (Gnadlinger, 2003). In Argentina, national
safe water programmes for local communities in arid regions of
Santiago del Estero Province installed ten rainwater catchments
and storage systems between 2000 and 2002 (Basán Nickisch,
2002). [WGII 13.2.5]
5.5.4.2
Adaptation: practices, options and constraints
Water management policies in Latin America need to be
relevant and should be included as a central point for adaptation
criteria. This will enhance the region’s capability to improve
its management of water availability. Adaptation to drier
conditions in approximately 60% of the Latin America region
will need large investments in water supply systems. Managing
trans-basin diversions has been the solution in many areas (e.g.,
Yacambu Basin in Venezuela, Alto Piura and Mantaro Basin
in Peru). Water conservation practices, water recycling and
optimisation of water consumption have been recommended
during water-stressed periods (COHIFE, 2003) (see Box 5.6).
[WGII 13.5]
Section 5
Analysing regional aspects of climate change and water resources
Box 5.6: Adaptation capacity of the South American highlands pre-Colombian communities.
[WGII Box 13.2]
The subsistence of indigenous civilisations in the Americas relied on the resources cropped under the prevailing climate
conditions around their settlements. In the highlands of today’s Latin America, one of the most critical limitations affecting
development was, and currently is, the irregular distribution of water. This situation is the result of the particularities of
atmospheric processes and extremes, the rapid runoff in the deep valleys, and the changing soil conditions. Glacier melt
was, and still is, a reliable source of water during dry seasons. However, the streams run into the valleys within bounded
water courses, bringing water only to certain locations. Since the rainfall seasonality is strong, runoff from glaciers is the
major dependable source of water during the dry season. Consequently, the pre-Colombian communities developed
different adaptive actions to satisfy their requirements. Today, the problem of achieving the necessary balance between
water availability and demand is practically the same, although the scale might be different.
Under such limitations, from today’s Mexico to northern Chile and Argentina, the pre-Colombian civilisations developed
the necessary capacity to adapt to the local environmental conditions. Such capacity involved their ability to solve some
hydraulic problems and foresee climate variations and seasonal rain periods. On the engineering side, their developments
included the use of captured rainwater for cropping, filtration and storage; and the construction of surface and underground
irrigation channels, including devices to measure the quantity of water stored (Figure 5.11) (Treacy, 1994; Wright and
Valencia Zegarra, 2000; Caran and Nelly, 2006). They were also able to interconnect river basins from the Pacific and
Atlantic watersheds, in the Cumbe valley and in Cajamarca (Burger, 1992).
Figure 5.11: Nasca (southern coast of Peru) system of water cropping for underground aqueducts and feeding the phreatic layers.
Other capacities were developed to foresee climatic variations and seasonal rain periods, to organise their sowing
schedules, and to programme their yields (Orlove et al., 2000). These efforts enabled the subsistence of communities
which, at the peak of the Inca civilisation, included some 10 million people in what is today Peru and Ecuador.
Their engineering capacities also enabled the rectification of river courses, as in the case of the Urubamba River, and the
building of bridges, either hanging ones or with pillars cast in the river bed. They also used running water for leisure and
worship purposes, as seen today in the ‘Baño del Inca’ (the spa of the Incas), fed from geothermal sources, and the ruins
of a musical garden at Tampumacchay in the vicinity of Cusco (Cortazar, 1968). The priests of the Chavin culture used
running water flowing within tubes bored into the structure of the temples in order to produce a sound like the roar of a
jaguar; the jaguar being one of their deities (Burger, 1992). Water was also used to cut stone blocks for construction. As
seen in Ollantaytambo, on the way to Machu Picchu, these stones were cut in regular geometric shapes by leaking water
into cleverly made interstices and freezing it during the Altiplano night, at below-zero temperatures. They also acquired
the capacity to forecast climate variations, such as those from El Niño (Canziani and Mata, 2004), enabling the most
convenient and opportune organisation of their foodstuff production. In short, they developed pioneering efforts to adapt
to adverse local conditions and define sustainable development paths.
Today, under the vagaries of weather and climate, exacerbated by the increasing greenhouse effect and the shrinkage
of the glaciers (Carey, 2005; Bradley et al., 2006), it would be extremely useful to revisit and update such adaptation
measures. Education and training of present community members on the knowledge and technical abilities of their
ancestors would be a way forward. ECLAC’s procedures for the management of sustainable development (Dourojeanni,
2000), when considering the need to manage the extreme climate conditions in the highlands, refer back to the preColombian irrigation strategies.
101
Section 5
Analysing regional aspects of climate change and water resources
Problems in education and public health services are
fundamental barriers to adaptation; for example, in the case of
extreme events (e.g., floods or droughts) mainly in poor rural
areas (Villagrán de León et al., 2003). [WGII 13.5]
5.6 North America
5.6.1
Context and observed change
Climate change will constrain North America’s already overallocated water resources, thereby increasing competition among
agricultural, municipal industrial, and ecological uses (very high
confidence). Some of the most important societal and ecological
impacts of climate change that are anticipated in this region stem
from changes in surface and groundwater hydrology. Table 5.7
outlines the changes observed in North America during the past
century, which illustrate the wide range of effects of a warming
climate on water resources. [WGII 14.ES]
As the rate of warming accelerates during the coming decades,
changes can be anticipated in the timing, volume, quality
and spatial distribution of freshwater available for human
settlements, agriculture and industrial users in most regions of
North America. While some of the water resource changes listed
above hold true for much of North America, 20th-century trends
suggest a high degree of regional variability in the impacts of
climate change on runoff, streamflow and groundwater recharge.
Variations in wealth and geography also contribute to an uneven
distribution of likely impacts, vulnerabilities, and capacities to
adapt in both Canada and the USA. [WGII 14.ES, 14.1]
5.6.2
Water resource change
Warming and changes in the form, timing and amount of
precipitation will be very likely to lead to earlier melting and
significant reductions in snowpack in the western mountains
by the middle of the 21st century. In projections for mountain
snowmelt-dominated watersheds, snowmelt runoff advances,
winter and early spring flows increase (raising flooding
potential), and summer flows decrease substantially. [WGII
14.4] Hence, over-allocated water systems of the western USA
and Canada that rely on capturing snowmelt runoff could be
Examples from AR4
1–4 week earlier peak
streamflow due to earlier
warming-driven snowmelt
US West and US New England
regions, Canada
[WGII 1.3, 14.2]
Proportion of precipitation
iiiiifalling as snow
Western Canada and prairies,
US West
[WGII 14.2, WGI 4.2]
Duration and extent of snow
iiiiicover
Most of North America
[WGI 4.2]
Annual precipitation
Mountain snow water
iiiiiequivalent
Annual precipitation
Frequency of heavy
iiiiiprecipitation events
Most of North America
[WGI 3.3]
Western North America
[WGI 4.2]
Central Rockies, south-western
USA, Canadian prairies and
eastern Arctic [WGII 14.2]
Most of USA
[WGII 14.2]
Runoff and streamflow
Colorado and Columbia River
Basins [WGII 14.2]
Widespread thawing of
iiiiipermafrost
Most of northern Canada and
Alaska [WGII 14.4, 15.7]
Water temperature of lakes
iiiii(0.1–1.5°C)
Most of North America
[WGII 1.3]
Streamflow
Most of the eastern USA
[WGII 14.2]
Glacial shrinkage
US western mountains, Alaska
and Canada [WGI 4.ES, 4.5]
Ice cover
Great Lakes, Gulf of St.
Lawrence [WGII 4.4, 14.2]
Projected change and consequences
5.6.2.1
Freshwater resources
Simulated future annual runoff in North American catchments
varies by region, general circulation model (GCM) and
emissions scenario. Annual mean precipitation is projected
to decrease in the south-western USA but increase over
most of the remainder of North America up to 2100. [WGI
11.5.3.2; WGII 14.3.1] Increases in precipitation in Canada are
projected to be in the range of +20% for the annual mean and
+30% for winter, under the A1B scenario. Some studies project
widespread increases in extreme precipitation [WGI 11.5.3.3;
WGII 14.3.1], but also droughts associated with greater
temporal variability in precipitation. In general, projected
changes in precipitation extremes are larger than changes in
mean precipitation. [WGI 10.3.6.1; WGII 14.3.1]
102
Table 5.7: Observed changes in North American
water resources during the past century ( = increase,
= decrease).
Salinisation of coastal
iiiiisurfacewaters
Periods of drought
Florida, Louisiana
[WGII 6.4]
Western USA, southern Canada
[WGII 14.2]
especially vulnerable, as are those systems that rely upon runoff
from glaciers. [WGII 14.2, 15.2]
In British Columbia, projected impacts include increased
winter precipitation, more severe spring floods on the coast
and the interior, and more summer droughts along the south
coast and southern interior, which would decrease streamflow
in these areas and affect both fish survival and water supplies
in the summer, when demand is the highest. In the Great Lakes,
projected impacts associated with lower water levels are likely
to exacerbate challenges relating to water quality, navigation,
recreation, hydropower generation, water transfers and binational relationships. [WGII 14.2, 14.4] Many, but not all,
assessments project lower net basin supplies and water levels
for the Great Lakes–St. Lawrence Basin. [WGII 14.ES, 14.2]
Section 5
Analysing regional aspects of climate change and water resources
With climate change, availability of groundwater is likely to
be influenced by three key factors: withdrawals (reflecting
development, demand, and availability of other sources),
evapotranspiration (increases with temperature) and recharge
(determined by temperature, timing and amount of precipitation,
and surface water interactions). Simulated annual groundwater
base flows and aquifer levels respond to temperature,
precipitation and pumping – decreasing in scenarios that are
drier or have higher pumping and increasing in scenarios that
are wetter. In some cases there are base flow shifts; increasing
in winter and decreasing in spring and early summer. [WGII
14.4.1] Increased evapotranspiration or groundwater pumping
in semi-arid and arid regions of North America may lead to
salinisation of shallow aquifers. [WGII 3.4] In addition, climate
change is likely to increase the occurrence of saltwater intrusion
into coastal aquifers as sea level rises. [WGII 3.4.2]
5.6.2.2
Energy
Hydropower production is known to be sensitive to total runoff,
to its timing, and to reservoir levels. During the 1990s, for
example, Great Lakes levels fell as a result of a lengthy drought,
and in 1999 hydropower production was down significantly
both at Niagara and Sault St. Marie (CCME, 2003). [WGII
4.2] For a 2–3°C warming in the Columbia River Basin and
British Columbia Hydro service areas, the hydro-electric
supply under worst-case water conditions for winter peak
demand will be likely to increase (high confidence). Similarly,
Colorado River hydropower yields will be likely to decrease
significantly (Christensen et al., 2004), as will Great Lakes
hydropower (Moulton and Cuthbert, 2000; Lofgren et al.,
2002; Mirza, 2004). Lower Great Lake water levels could lead
to large economic losses (Canadian $437–660 million/yr), with
increased water levels leading to small gains (Canadian $28–
42 million/yr) (Buttle et al., 2004; Ouranos, 2004). Northern
Québec hydropower production would be likely to benefit
from greater precipitation and more open water conditions, but
hydro plants in southern Québec would be likely to be affected
by lower water levels. Consequences of changes in seasonal
distribution of flows and in the timing of ice formation are
uncertain (Ouranos, 2004). [WGII 3.5, 14.4.8]
Solar resources could be affected by future changes in
cloudiness, which could slightly increase the potential for
solar energy in North America south of 60°N (based on many
models and the A1B emissions scenario for 2080–2099 versus
1980–1999). [WGI Figure 10.10] Pan et al. (2004), however,
projected the opposite; that increased cloudiness will decrease
the potential output of photovoltaics by 0–20% (based on the
HadCM2 and RegCM224 models with an idealised scenario of
CO2 increase). [WGII 14.4.8] Bioenergy potential is climatesensitive through direct impacts on crop growth and availability
of irrigation water. Bioenergy crops are projected to compete
successfully for agricultural acreage at a price of US$33/106
g, or about US$1.83/109 joules (Walsh et al., 2003). Warming
and precipitation increases are expected to allow the bioenergy
24
crop, switchgrass, to compete effectively with traditional crops
in the central USA (based on the RegCM2 model and doubled
CO2 concentration) (Brown et al., 2000). [WGII 14.4.8]
5.6.2.3
Health
Water-borne disease outbreaks from all causes are distinctly
seasonal in North America, clustered in key watersheds, and
associated with heavy precipitation (in the USA: Curriero et al.,
2001) or with extreme precipitation and warmer temperatures
(in Canada: Thomas et al., 2006). Heavy runoff after severe
rainfall can also contaminate recreational waters and increase
the risk of human illness (Schuster et al., 2005) through
higher bacterial counts. This association is often strongest
at beaches close to rivers (Dwight et al., 2002). Water-borne
diseases and degraded water quality are very likely to increase
with more heavy precipitation. Food-borne diseases also
show some relationship with temperature trends. In Alberta,
ambient temperature is strongly, but non-linearly, associated
with the occurrence of enteric pathogens (Fleury et al., 2006).
[WGII 14.ES, 14.2.5]
An increase in intense tropical cyclone activity is likely. [WGI
SPM] Storm surge flooding is already a problem along the Gulf
of Mexico and South Atlantic coasts of North America. The
death toll from Hurricane Katrina in 2005 is estimated at 1,800
[WGII 6.4.2], with some deaths and many cases of diarrhoeal
illness associated with contamination of water supplies (CDC,
2005; Manuel, 2006). [WGII 8.2.2; see also Section 4.5
regarding riverine flooding]
5.6.2.4
Agriculture
Research since the TAR supports the conclusion that moderate
climate change will be likely to increase yields of North American
rain-fed agriculture, but with smaller increases and more spatial
variability than in earlier estimates (high confidence) (Reilly,
2002). Many crops that are currently near climate thresholds,
however, are projected to suffer decreases in yields, quality, or
both, with even modest warming (medium confidence) (Hayhoe
et al., 2004; White et al., 2006). [WGII 14.4.4]
The vulnerability of North American agriculture to climatic
change is multidimensional and is determined by interactions
between pre-existing conditions, indirect stresses stemming
from climate change (e.g., changes in pest competition, water
availability), and the sector’s capacity to cope with multiple,
interacting factors, including economic competition from
other regions as well as improvements in crop cultivars and
farm management (Parson et al., 2003). Water availability is
the major factor limiting agriculture in south-east Arizona, but
farmers in the region perceive that technologies and adaptations
such as crop insurance have recently decreased vulnerability
(Vasquez-Leon et al., 2003). Areas with marginal financial
and resource endowments (e.g., the US northern plains) are
especially vulnerable to climate change (Antle et al., 2004).
Unsustainable land-use practices will tend to increase the
See Appendix I for model descriptions.
103
Section 5
Analysing regional aspects of climate change and water resources
vulnerability of agriculture in the US Great Plains to climate
change (Polsky and Easterling, 2001). [WGII 14.4.4; see also
Section 4.2.2] Heavily utilised groundwater-based systems in
the south-west USA are likely to experience additional stress
from climate change that leads to decreased recharge (high
confidence), thereby impacting agricultural productivity.
[WGII 14.4.1]
Decreases in snow cover and more winter rain on bare soil
are likely to lengthen the erosion season and enhance erosion,
increasing the potential for water quality impacts in agricultural
areas. Soil management practices (e.g., crop residue, no-till) in
the North American grainbelt may not provide sufficient erosion
protection against future intense precipitation and associated
runoff (Hatfield and Pruger, 2004; Nearing et al., 2004).
[WGII 14.4.1]
5.6.2.5
Biodiversity
A wide range of species and biomes could be affected by the
projected changes in rainfall, soil moisture, surface water levels
and streamflow in North America during the coming decades.
The lowering of lake and pond water levels, for example, can lead
to reproductive failure in amphibians and fish, and differential
responses among species can alter aquatic community
composition and nutrient flows. Changes in rainfall patterns
and drought regimes can facilitate other types of ecosystem
disturbances, including fire (Smith et al., 2000) and biological
invasion (Zavaleta and Hulvey, 2004). [WGII 14.4.2] Landward
replacement of grassy freshwater marshes by more salt-tolerant
mangroves, e.g., in the south-eastern Florida Everglades since
the 1940s, has been attributed to the combined effects of sealevel rise and water management, resulting in lowered water
tables (Ross et al., 2000). [WGII 1.3.3.2] Changes in freshwater
runoff to the coast can alter salinity, turbidity and other aspects
of water quality that determine the productivity and distribution
of plant and animal communities. [WGII 6.4]
At high latitudes, several models simulate increased net
primary productivity of North American ecosystems as a
result of expansion of forests into the tundra, plus longer
growing seasons (Berthelot et al., 2002), depending largely
on whether there is sufficient enhancement of precipitation to
offset increased evapotranspiration in a warmer climate. Forest
growth appears to be slowly accelerating in regions where tree
growth has historically been limited by low temperatures and
short growing seasons. Growth is slowing, however, in areas
subject to drought. Radial growth of white spruce on dry southfacing slopes in Alaska has decreased over the last 90 years,
due to increased drought stress (Barber et al., 2000). Modelling
experiments by Bachelet et al. (2001) project the areal extent of
drought-limited ecosystems to increase 11% per 1ºC warming
in the continental USA. [WGII 14.4] In North America’s Prairie
Pothole region, models have projected an increase in drought
with a 3°C regional temperature increase and varying changes in
precipitation, leading to large losses of wetlands and to declines
in the populations of waterfowl breeding there (Johnson et al.,
2005). [WGII 4.4.10]
104
Ecological sustainability of fish and fisheries productivity are
closely tied to water supply and water temperature. It is likely
that cold-water fisheries will be negatively affected by climate
change; warm-water fisheries will generally gain; and the results
for cool-water fisheries will be mixed, with gains in the northern
and losses in the southern portions of their ranges. Salmonids,
which prefer cold, clear water, are likely to experience the
most negative impacts (Gallagher and Wood, 2003). Arctic
freshwater fisheries are likely to be most affected, as they will
experience the greatest warming (Wrona et al., 2005). In Lake
Erie, larval recruitment of river-spawning walleye will depend
on temperature and flow changes, but lake-spawning stocks will
be likely to decline due to the effects of warming and lower lake
levels (Jones et al., 2006). The ranges of warm-water species
will tend to shift northwards or to higher altitudes (Clark et al.,
2001; Mohseni et al., 2003) in response to changes in water
temperature. [WGII 14.4]
5.6.2.6
Case studies of climate change impacts in large
iiiiiiiiiiiiiiiiwatersheds in North America
Boxes 5.7 and 5.8 describe two cases that illustrate the potential
impacts and management challenges posed by climate change
in ‘water-scarce’ and ‘water-rich’ environments in western
North America: the Colorado and the Columbia River Basins,
respectively.
5.6.3
Adaptation
Although North America has considerable capacity to adapt
to the water-related aspects of climate change, actual practice
has not always protected people and property from the adverse
impacts of floods, droughts, storms and other extreme weather
events. Especially vulnerable groups include indigenous peoples
and those who are socially or economically disadvantaged.
Traditions and institutions in North America have encouraged a
decentralised response framework where adaptation tends to be
reactive, unevenly distributed, and focused on coping with rather
than preventing problems. Examples of adaptive behaviour
influenced exclusively or predominantly by projections of
climate change and its effects on water resources are largely
absent from the literature. [WGII 14.5.2] A key prerequisite
for sustainability in North America is ‘mainstreaming’ climate
issues into decision making. [WGII 14.7]
The vulnerability of North America depends on the
effectiveness of adaptation and the distribution of coping
capacity; both of which are currently uneven and have not
always protected vulnerable groups from the adverse impacts
of climate variability and extreme weather events. [WGII 14.7]
The USA and Canada are developed economies with extensive
infrastructure and mature institutions, with important regional
and socio-economic variation (NAST, 2000; Lemmen and
Warren, 2004). These capabilities have led to adaptation and
coping strategies across a wide range of historical conditions,
with both successes and failures. Most studies on adaptive
strategies consider implementation based on past experiences
(Paavola and Adger, 2002). [WGII 14.5]
Section 5
Analysing regional aspects of climate change and water resources
Box 5.7: Drought and climatic changes in the Colorado River Basin.
The Colorado River supplies much of the water needs of seven US states, two Mexican states, and thirty-four Native
American tribes (Pulwarty et al., 2005). These represent a population of 25 million inhabitants with a projection of 38 million
by the year 2020. Over the past 100 years the total area affected by severe or extreme climatological drought in the USA
has averaged around 14% each year with this percentage having been as high as 65% in 1934.
The westward expansion of population and economic activities, and concurrent responses to drought events, have resulted
in significant structural adaptations, including hundreds of reservoirs, irrigation projects and groundwater withdrawals,
being developed in semi-arid environments. As widely documented, the allocation of Colorado River water to basin states
occurred during the wettest period in over 400 years (i.e., 1905–1925). Recently, the western USA has experienced
sustained drought, with 30–40% of the region under severe drought since 1999, and with the lowest 5-year period of
Colorado River flow on record occurring from 2000 to 2004. At the same time, the states of the south-west USA are
experiencing some of the most rapid growth in the country, with attendant social, economic and environmental demands
on water resources, accompanied by associated legal conflicts (Pulwarty et al., 2005).
Only a small portion of the full Colorado Basin area (about 15%) supplies most (85%) of its flow. Estimates show that,
with increased climatic warming and evaporation, concurrent runoff decreases would reach 30% during the 21st century
(Milly et al., 2005). Under such conditions, together with projected withdrawals, the requirements of the Colorado River
Compact may only be met 60–75% of the time by 2025 (Christensen et al., 2004). Some studies estimate that, by 2050,
the average moisture conditions in the south-western USA could equal the conditions observed in the 1950s. These
changes could occur as a consequence of increased temperatures (through increased sublimation, evaporation and soil
moisture reduction), even if precipitation levels remain fairly constant. Some researchers argue that these assessments,
because of model choice, may actually underestimate future declines.
Most scenarios of Colorado River flow at Lees Ferry (which separates the upper from the lower basin) indicate that, within
20 years, discharge may be insufficient to meet current consumptive water resource demands. The recent experience
illustrates that ‘critical’ conditions already exist in the basin (Pulwarty et al., 2005). Climate variability and change, together
with increasing development pressures, will result in drought impacts that are beyond the institutional experience in the
region and will exacerbate conflicts among water users.
North American agriculture has been exposed to many severe
weather events during the past decade. More variable weather,
coupled with out-migration from rural areas and economic
stresses, has increased the vulnerability of the agricultural
sector overall, raising concerns about its future capacity to cope
with a more variable climate (Senate of Canada, 2003; Wheaton
et al., 2005). North American agriculture is, however, dynamic.
Adaptation to multiple stresses and opportunities, including
changes in markets and weather, is a normal process for the
sector. Crop and enterprise diversification, as well as soil and
water conservation, are often used to reduce weather-related
risks (Wall and Smit, 2005). [WGII 14.2.4]
Many cities in North America have initiated ‘no regrets’ actions
based on historical experience (MWD, 2005). [WGII Box
14.3] Businesses in Canada and the USA are also investing in
adaptations relevant to changes in water resources, though few
of these appear to be based on future climate change projections.
[WGII 14.5.1] Examples of these types of adaptations include
the following.
• Insurance companies are investing in research to prevent
future hazard damage to insured property, and to adjust
pricing models (Munich Re, 2004; Mills and Lecompte,
2006). [WGII 14.2.4]
• Ski resort operators are investing in lifts to reach higher
•
•
•
•
•
•
altitudes and in equipment to compensate for declining
snow cover (Elsasser et al., 2003; Census Bureau, 2004;
Scott, 2005; Jones and Scott, 2006; Scott and Jones, 2006).
[WGII 14.2.4]
New York has reduced total water consumption by 27%
and per capita consumption by 34% since the early 1980s
(City of New York, 2005). [WGII 14.2.4]
In the Los Angeles area, incentive and information
programmes of local water districts encourage water
conservation (MWD, 2005). [WGII Box 14.3]
With highly detailed information on weather conditions,
farmers are adjusting crop and variety selection, irrigation
strategies and pesticide applications (Smit and Wall, 2003).
[WGII 14.2.4]
The City of Peterborough, Canada, experienced two 100year flood events within 3 years; it responded by flushing
the drainage systems and replacing the trunk sewer systems
to meet more extreme 5-year flood criteria (Hunt, 2005).
[WGII 14.5.1]
Recent droughts in six major US cities, including New
York and Los Angeles, led to adaptive measures involving
investments in water conservation systems and new water
supply/distribution facilities (Changnon and Changnon,
2000). [WGII 14.5.1]
To cope with a 15% increase in heavy precipitation,
105
Section 5
Analysing regional aspects of climate change and water resources
Box 5.8: Climate change adds challenges to managing the Columbia River Basin.
[WGII Box 14.2]
Current management of water in the Columbia River basin involves balancing complex, often competing, demands for
hydropower, navigation, flood control, irrigation, municipal uses, and maintenance of several populations of threatened
and endangered species (e.g., salmon). Current and projected needs for these uses over-commit existing supplies.
Water management in the basin operates in a complex institutional setting, involving two sovereign nations (Columbia
River Treaty, ratified in 1964), aboriginal populations with defined treaty rights (‘Boldt decision’ in U.S. vs. Washington in
1974), and numerous federal, state, provincial and local government agencies (Miles et al., 2000; Hamlet, 2003). Pollution
(mainly non-point source) is an important issue in many tributaries. The first-in-time first-in-right provisions of western
water law in the U.S. portion of the basin complicate management and reduce water available to junior water users (Gray,
1999; Scott et al., 2004). Complexities extend to different jurisdictional responsibilities when flows are high and when they
are low, or when protected species are in tributaries, the main stem or ocean (Miles et al., 2000; Mote et al., 2003).
With climate change, projected annual Columbia River flow changes relatively little, but seasonal flows shift markedly
toward larger winter and spring flows and smaller summer and autumn flows (Hamlet and Lettenmaier, 1999; Mote et al.,
1999). These changes in flows will be likely to coincide with increased water demand, principally from regional growth
but also induced by climate change. Loss of water availability in summer would exacerbate conflicts, already apparent
in low-flow years, over water (Miles et al. 2000). Climate change is also projected to impact urban water supplies within
the basin. For example, a 2°C warming projected for the 2040s would increase demand for water in Portland, Oregon, by
5.7 million m3/yr with an additional demand of 20.8 million m3/yr due to population growth, while decreasing supply by 4.9
million m3/yr (Mote et al., 2003). Long-lead climate forecasts are increasingly considered in the management of the river
but in a limited way (Hamlet et al., 2002; Lettenmaier and Hamlet, 2003; Gamble et al., 2004; Payne et al., 2004). Each of
43 sub-basins of the system has its own sub-basin management plan for fish and wildlife, none of which comprehensively
addresses reduced summertime flows under climate change (ISRP/ISAB, 2004).
The challenges of managing water in the Columbia River basin are likely to expand with climate change due to changes
in snowpack and seasonal flows (Miles et al., 2000; Parson et al., 2001; Cohen et al., 2003). The ability of managers to
meet operating goals (reliability) is likely to drop substantially under climate change (as projected by the HadCM2 and
ECHAM4/OPYC3 AOGCMs under the IPCC IS92a emissions scenario for the 2020s and 2090s) (Hamlet and Lettenmaier,
1999). Reliability losses are projected to reach 25% by the end of the 21st century (Mote et al., 1999) and interact with
operational rule requirements. For example, ‘fishfirst’ rules would reduce firm power reliability by 10% under the present
climate and by 17% in years during the warm phase of the Pacific Decadal Oscillation (PDO). Adaptive measures have the
potential to moderate the impact of the decrease in April snowpack but could lead to 10 to 20% losses of firm hydropower
and lower than current summer flows for fish (Payne et al., 2004). Integration of climate change adaptation into regional
planning processes is in the early stages of development (Cohen et al., 2006).
•
•
106
Burlington and Ottawa, Ontario, employed both structural
and non-structural measures, including directing
downspouts to lawns in order to encourage infiltration, and
increasing depression and street detention storage (Waters
et al., 2003). [WGII 14.5.1]
A population increase of over 35% (nearly one million
people) since 1970 has increased water use in Los Angeles
by only 7% (California Regional Assessment Group, 2002),
due largely to conservation practices. [WGII Box 14.3]
The Regional District of Central Okanagan in British
Columbia produced a water management plan in 2004 for
a planning area known as the Trepanier Landscape Unit,
which explicitly addresses climate scenarios, projected
changes in water supply and demand, and adaptation
options (Cohen et al., 2004; Summit Environmental
Consultants, 2004). [WGII Box 3.1, 20.8.2]
5.7 Polar regions
5.7.1
Context
The polar regions are the areas of the globe expected to
experience some of the earliest and most profound climateinduced changes, largely because of their large cryospheric
components that also dominate their hydrological processes
and water resources. Most concern about the effect of changing
climate on water resources of the polar regions has been
expressed for the Arctic. For the Antarctic, the focus has been
on the mass balance of the major ice sheets and their influence
on sea level, and to a lesser degree, induced changes in some
aquatic systems. The Arctic contains a huge diversity of
water resources, including many of the world’s largest rivers
Analysing regional aspects of climate change and water resources
Section 5
(Lena, Ob, Mackenzie and Yenisey), megadeltas (Lena and
Mackenzie), large lakes (e.g., Great Bear), extensive glaciers
and ice caps, and expanses of wetlands. Owing to a relatively
small population (4 million: Bogoyavlenskiy and Siggner, 2004)
and severe climate, water-resource-dependent industries such
as agriculture and forestry are quite small-scale, whereas there
are numerous commercial and subsistence fisheries. Although
some nomadic peoples are still significant in some Arctic
countries, populations are becoming increasingly concentrated
in larger communities (two-thirds of the population now live in
settlements with more than 5,000 inhabitants) although most
of these are located near, and dependent on, transportation
on major water routes. Relocation to larger communities has
led to increased access to, for example, treated water supplies
and modern sewage disposal (Hild and Stordhal, 2004). [WGI
10.6.4; WGII 15.2.1]
A significant proportion of the Arctic’s water resources originate
in the headwater basins of the large rivers that carry flow
through the northern regions to the Arctic Ocean. The flows of
these rivers have been the focus of significant hydro-electric
development and remain some of the world’s largest untapped
hydropower potential (e.g., Shiklomanov et al., 2000; Prowse
et al., 2004). Given the role of these rivers in transporting heat,
sediment, nutrients, contaminants and biota into the north,
climate-induced changes at lower latitudes exert a strong effect
on the Arctic. Moreover, it is changes in the combined flow
of all Arctic catchments that have been identified as being so
important to the freshwater budget of the Arctic Ocean, sea-ice
production and, ultimately, potential effects on thermohaline
circulation and global climate. [WGI 10.3.4; WGII 15.4.1]
5.7.2
Observed changes
The most significant observed change to Arctic water resources
has been the increase since the 1930s in the combined flow
from the six largest Eurasian Rivers (approximately 7%:
Peterson et al., 2002). Increased runoff to the Arctic Ocean
from circumpolar glaciers, ice caps and the Greenland ice
sheet has also been noted to have occurred in the late 20th
century and to be comparable to the increase in combined
river inflow from the largest pan-Arctic rivers (Dyurgerov
and Carter, 2004). Changes in mass balance of ice masses is
related to a complex response to changes in precipitation and
temperature, resulting in opposing regional trends such as are
found between the margins and some interior portions of the
Greenland ice sheet (Abdalati and Steffen, 2001; Johannessen
et al., 2005; Walsh et al., 2005). In the case of flow increases
on the Eurasian rivers, potential controlling factors, such
as ice melt from permafrost, forest-fire effects and dam
storage variations, have been eliminated as being responsible
(McClelland et al., 2004), and one modelling study suggests
that anthropogenic climate forcing factors have played a role.
Evaluating the effects of climate and other factors on the
largest Arctic-flowing river in North America, the Mackenzie
River, has proven particularly difficult because of the large
dampening effects on flow created by natural storage-release
effects of major lakes and reservoirs (e.g., Gibson et al., 2006;
Peters et al., 2006). [WGI 9.5.4; WGII 15.4.1.1]
The effects of precipitation on runoff are difficult to ascertain,
largely because of the deficiencies and sparseness of the Arctic
precipitation network, but it is believed to have risen slowly
by approximately 1% per decade (McBean et al., 2005; Walsh
et al., 2005). Changes in the magnitude of winter discharge
on major Arctic rivers have also been observed and linked to
increased warming and winter precipitation in the case of the
Lena River (Yang et al., 2002; Berezovskaya et al., 2005) but,
although also previously thought to be climate-induced, simply
to hydro-electric regulation on the Ob and Yenisei Rivers (Yang
et al., 2004a, b). Changes have also occurred in the timing of
the spring freshet, the dominant flow event on Arctic rivers, but
these have not been spatially consistent over the last 60 years,
with adjacent Siberian rivers showing both advancing (Lena:
Yang et al., 2002) and delaying (Yenisei: Yang et al., 2004b)
trends. Floating freshwater ice also controls the seasonal
dynamics of Arctic rivers and lakes, particularly flooding
regimes, and although there has been no reported change in
ice-induced flood frequency or magnitude, ice-cover duration
has decreased in much of the sub-Arctic (Walsh et al., 2005).
[WGII 15.2.1, 15.4.1.1]
Significant changes to permafrost have occurred in the Arctic in
the last half-century (Walsh et al., 2005) and, given the role of
frozen ground in controlling flow pathways, thawing permafrost
could be influencing seasonal precipitation-runoff responses
(Serreze et al., 2003; Berezovskaya et al., 2005; Zhang et al.,
2005). Permafrost thaw, and the related increase in substrate
permeability, has also been suspected of producing changes
in lake abundance in some regions of Siberia during a threedecade period at the end of the 20th century (Smith et al., 2005;
see Figure 5.12). At higher latitudes, initial thaw is thought to
have increased surface ponding and lake abundance whereas, at
lower latitudes, lake abundance has declined as more extensive
and deeper thaw has permitted ponded water to drain away to
the sub-surface flow systems. In broader areas of the Arctic, the
biological composition of lake and pond aquatic communities
has been shown to respond to shifts in increasing mean annual
and summer air temperatures and related changes in thermal
stratification/stability and ice-cover duration (Korhola et al.
2002; Ruhland et al., 2003; Pienitz et al., 2004; Smol et al.,
2005; Prowse et al., 2006). [WGI Chapter 4; WGII 15.4.1.1]
Freshwater aquatic ecosystems of the Antarctic have also
been shown to be highly responsive to variations in climate,
particularly to air temperature, although trends in such have
varied across the continent. Productivity of lakes in the Dry
Valleys, for example, has been observed to decline with
decreasing air temperature (e.g., Doran et al., 2002). By contrast,
rising air temperatures on the maritime sub-Antarctic Signy
Island have produced some of the fastest and most amplified
responses in lake temperature yet documented in the Southern
Hemisphere (Quayle et al., 2002). Moreover, warming effects on
snow and ice cover have produced a diverse array of ecosystem
disruptions (Quayle et al., 2003). [WGII 15.2.2.2]
107
Analysing regional aspects of climate change and water resources
Section 5
Runoff in both polar regions will be augmented by the
wastage of glaciers, ice caps and the ice sheets of Greenland
and Antarctica, although some ice caps and the ice sheets
contribute most of their melt water directly to their surrounding
oceans. More important to the terrestrial water resources are
the various glaciers scattered throughout the Arctic, which are
projected to largely retreat with time. While initially increasing
streamflow, a gradual disappearance or a new glacier balance at
smaller extents will eventually result in lower flow conditions,
particularly during the drier late-summer periods, critical periods
for aquatic Arctic biota. [WGI Chapter 10; WGII 15.4.1.3]
Figure 5.12: Locations of Siberian lakes that have
disappeared after a three-decade period of rising soil and
air temperatures (changes registered from satellite imagery
from the early 1970s to 1997–2004), overlaid on various
permafrost types. The spatial pattern of lake disappearance
suggests that permafrost thawing has driven the observed
losses. From Smith et al. (2005). Reprinted with permissions
from AAAS. [WGII Figure 15.4]
5.7.3
Projected changes
Projecting changes in the hydrology, and thus water resources,
of the Arctic are problematic because of strong variability in
the seasonality and spatial patterns of the precipitation among
GCM models. Although most predict an increase, prediction of
runoff from precipitation inputs is confounded by problems in
apportioning rain and snow as the region warms, or as additional
moisture sources become available with the retreat of sea ice. In
general, however, the latest projections for runoff from the major
Arctic catchments indicate an overall increase in the range of
10–30%. One factor not included in such projections, however,
is the rise in evapotranspiration that will occur as the dominating
terrestrial vegetation shifts from non-transpiring tundra lichens
to various woody species (e.g., Callaghan et al., 2005), although
this might be offset by CO2-induced reductions in transpiration
(e.g., Gedney et al., 2006). Similarly not factored into current
runoff projections are the effects of future permafrost thaw and
deepening of active layers (Anisimov and Belolutskaia, 2004;
Instanes et al., 2005), which will increasingly link surface
and groundwater flow regimes, resulting in major changes in
seasonal hydrographs. Associated wetting or drying of tundra,
coupled with warming and increased active-layer depth, will
determine its source/sink status for carbon and methane fluxes.
Permafrost thaw and rising discharge is also expected to
cause an increase in river sediment loads (Syvitski, 2002) and
potential major transformations to channel networks (Bogaart
and van Balen, 2000; Vandenberghe, 2002). [WGI Chapter 10;
WGII 15.4.2.3, 15.4.1.2]
108
Projected warming also implies a continuation of recent trends
toward later freeze-up and earlier break-up of river and lake ice
(Walsh et al., 2005) and reductions in ice thickness, which will
lead to changes in lake thermal structures, quality/quantity of
under-ice habitat, and effects on river-ice jamming and related
flooding (Beltaos et al., 2006; Prowse et al., 2006). The latter is
important as a hazard to many river-based northern settlements
but is also critical to sustaining the ecological health of riparian
ecosystems that rely on the spring inundation of water, sediment
and nutrients (Prowse et al., 2006). [WGII 15.4.1.2, 15.6.2]
The above major alterations to the cold-region hydrology of
the Arctic will alter aquatic biodiversity, productivity, seasonal
habitat availability and geographical distribution of species,
including major fisheries populations (Prowse et al., 2006;
Reist et al. 2006a, b, c; Wrona et al., 2006). Arctic peoples,
functioning in subsistence and commercial economies, obtain
many services from freshwater ecosystems (e.g., harvestable
biota), and changes in the abundance, replenishment, availability
and accessibility of such resources will alter local resource
use and traditional lifestyles (Nuttall et al., 2005; Reist et al.,
2006a). [WGII 15.4.1.3]
Given that the Arctic is projected to be generally ‘wetter’, a
number of hydrological processes will affect the pathways
and increase the loading of pollutants (e.g., persistent organic
pollutants and mercury) to Arctic aquatic systems (MacDonald
et al., 2003). Changes in aquatic trophic structure and food
webs (Wrona et al., 2006) have the further potential to alter
the accumulation of bio-magnifying chemicals. This has special
health concerns for northern residents who rely on traditional
sources of local food. Changes to the seasonal timing and
magnitude of flows and available surface water will also be of
concern for many northern communities that rely on surface
and/or groundwater, often untreated, for drinking water (United
States Environmental Protection Agency, 1997; Martin et al.,
2005). Risks of contamination may also increase with the
northward movement of species and related diseases, and via
sea-water contamination of groundwater reserves resulting
from sea-level rise in coastal communities (Warren et al., 2005).
[WGII 15.4.1]
The large amount of development and infrastructure that tends
to be concentrated near Arctic freshwater systems will be
strongly affected by changes in northern hydrological regimes.
Important examples include the decline of ice-road access to
Analysing regional aspects of climate change and water resources
Section 5
transport equipment and to northern communities; alterations
in surface and groundwater availability to communities and
industry; loss of containment security of mine wastes in
northern lakes underlain by permafrost; and increased flow and
ice hazards to instream drilling platforms and hydro-electric
reservoirs (World Commission on Dams, 2000; Prowse et al,
2004; Instanes et al., 2005). Although the future electricity
production of the entire Arctic has not been assessed, it has
been estimated for an IS92a emissions scenario that the
hydropower potential for plants existing at the end of the 20th
century will increase by 15–30% in Scandinavia and northern
Russia. [WGI 3.5.1; WGII 15.4.1.4]
5.7.4
Adaptation and vulnerability
A large amount of the overall vulnerability of Arctic freshwater
resources to climate change relates to the abrupt changes
associated with solid-to-liquid water-phase changes that will
occur in many of the cryospheric hydrological systems. Arctic
freshwater ecosystems have historically been able to adapt to
large variations in climate, but over protracted periods (e.g.,
Ruhland et al., 2003). The rapid rates of change over the
coming century, however, are projected to exceed the ability
of some biota to adapt (Wrona et al., 2006), and to result in
more negative than positive impacts on freshwater ecosystems
(Wrona et al., 2005). [WGII 15.2.2.2]
From a human-use perspective, potential adaptation measures
are extremely diverse, ranging from measures to facilitate
use of water resources (e.g., changes in ice-road construction
practices, increased open-water transportation, flow regulation
for hydro-electric production, harvesting strategies, and
methods of drinking-water access) to adaptation strategies
to deal with increased/decreased freshwater hazards (e.g.,
protective structures to reduce flood risks or increase flows for
aquatic systems; Prowse and Beltaos, 2002). Strong cultural
and/or social ties to traditional uses of water resources by some
northern peoples, however, could complicate the adoption of
some adaptation strategies (McBean et al., 2005; Nuttall et al.,
2005). [WGII 15.2.2.2]
5.8 Small islands
5.8.1
Context
The TAR (Chapter 17; IPCC, 2001b) noted that Small Island
States share many similarities (e.g., physical size, proneness
to natural disasters and climate extremes, extreme openness
of economies, low risk-spreading and adaptive capacity) that
enhance their vulnerability and reduce their resilience to climate
variability and change. In spite of differences in emphasis and
sectoral priorities on different islands, three common themes
emerge.
1. All Small Island States National Communications25
emphasise the urgency for adaptation action and the
financial resources to support such action.
2. Freshwater is seen as a critical issue in all Small Island
States, both in terms of water quality and quantity.
3. Many Small Island States, including all of the
Small Island Developing States (SIDS), see the
need for greater integrated watershed planning and
management.
[WGII TAR Chapter 17]
Water is a multi-sectoral resource that links to all facets of life
and livelihood, including security. Reliability of water supply
is viewed as a critical problem on many islands at present
and one whose urgency will increase in the future. There is
strong evidence that, under most climate change scenarios,
water resources in small islands are likely to be seriously
compromised (very high confidence). Most small islands have
a limited water supply, and water resources in these islands
are especially vulnerable to future changes and distribution of
rainfall. The range of adaptive measures considered, and the
priorities assigned, are closely linked to each country’s key
socio-economic sectors, its key environmental concerns, and
areas most at risk of climate change impacts such as sea-level
rise. [WGII 16.ES, 16.5.2]
5.8.2
Observed climatic trends and projections
iiiiiiiiiiiiiiiiin island regions
Hydrological conditions, water supply and water usage on
small islands pose quite different research and adaptation
problems compared with those in continental situations. These
need to be investigated and modelled over a range of island
types, covering different geology, topography and land cover,
and in light of the most recent climate change scenarios and
projections. [WGII 16.7.1] New observations and re-analyses
of temperatures averaged over land and ocean surfaces since
the TAR show consistent warming trends in all small-island
regions over the 1901 to 2004 period. However, the trends
are not linear and a lack of historical record keeping severely
hinders trend analysis. [WGII 16.2.2.2]
Recent studies show that the annual and seasonal ocean surface
and island air temperatures have increased by 0.6–1.0°C since
1910 throughout a large part of the South Pacific, south-west of
the South Pacific Convergence Zone (SPCZ),26 whereas decadal
increases of 0.3–0.5°C in annual temperatures are only widely
seen since the 1970s, preceded by some cooling after the 1940s,
which is the beginning of the record, to the north-east of the
SPCZ (Salinger, 2001; Folland et al., 2003). For the Caribbean,
Indian Ocean and Mediterranean regions, analyses shows that
warming ranged from 0.24°C to 0.5°C per decade for the 1971 to
2004 period. Some high-latitude regions, including the western
Canadian Arctic Archipelago, have experienced warming at a
Under the UN Framework Convention for Climate Change (UNFCCC), countries are required to provide periodic national communications on
their progress in reducing net GHG emissions, policies and measures enacted, and needs assessments.
26
The SPCZ is part of the ITCZ and is a band of low-level convergence, cloudiness and precipitation extending from the west Pacific warm pool
south-eastwards towards French Polynesia.
109
25
Section 5
Analysing regional aspects of climate change and water resources
more rapid pace than the global mean (McBean et al., 2005).
[WGII 16.2.2.2]
Trends in extreme daily rainfall and temperature across the
South Pacific for the period 1961–2003 show increases in the
annual number of hot days and warm nights, with decreases in
the annual number of cool days and cold nights, particularly
in years after the onset of El Niño, with extreme rainfall
trends generally less spatially coherent than those of extreme
temperature (Manton et al., 2001; Griffiths et al., 2003). In the
Caribbean, the percentage of days with very warm temperature
minima or maxima increased strongly since the 1950s, while the
percentage of days with cold temperatures decreased (Petersen
et al., 2002). [WGII 16.2.2.2]
For the Caribbean, a 1.5–2°C increase in global air temperature is
projected to affect the region through [WGII TAR Chapter 17]:
•
increases in evaporation losses,
•
decreased precipitation (continuation of a trend of rainfall
decline observed in some parts of the region),
•
reduced length of the rainy season – down 7–8% by 2050,
•
increased length of the dry season – up 6–8% by 2050,
•
increased frequency of heavy rains – up 20% by 2050,
•
increased erosion and contamination of coastal areas.
Variations in tropical and extra-tropical cyclones, hurricanes
and typhoons in many small-island regions are dominated by
ENSO and decadal variability. These result in a redistribution
of tropical storms and their tracks such that increases in one
basin are often compensated by decreases in other basins. For
example, during an El Niño event, the incidence of hurricanes
typically decreases in the Atlantic and far-western Pacific and
Australasian regions, while it increases in the central, north
and south Pacific, and especially in the western North Pacific
typhoon region. There is observational evidence for an increase
in intense tropical cyclone activity in the North Atlantic since
about 1970, correlated with increases in tropical SSTs. There
are also suggestions of increases in intense tropical cyclone
activity in other regions where concerns over data quality are
greater. Multi-decadal variability and the quality of records
prior to about 1970 complicate the detection of long-term
trends. Estimates of the potential destructiveness of tropical
cyclones suggest a substantial upward trend since the mid1970s. [WGI TS, 3.8.3; WGII 16.2.2.2]
Analyses of sea-level records having at least 25 years of hourly
data from stations installed around the Pacific Basin show
an overall average mean relative sea-level rise of 0.7 mm/yr
(Mitchell et al., 2001). Focusing only on the island stations with
more than 50 years of data (only four locations), the average
rate of sea-level rise (relative to the Earth’s crust) is 1.6 mm/yr.
[WGI 5.5.2]
5.8.2.1
Water
Table 5.8, based on seven GCMs and for a range of SRES
emissions scenarios, compares projected precipitation changes
over small islands by region. In the Caribbean, many islands
are expected to experience increased water stress as a result of
110
climate change, with all SRES scenarios projecting reduced
rainfall in summer across the region. It is unlikely that demand
would be met during low rainfall periods. Increased rainfall
in the Northern Hemisphere winter is unlikely to compensate,
due to a combination of lack of storage and high runoff during
storms. [WGII 16.3.1]
Table 5.8: Projected change in precipitation over small
islands, by region (%). Ranges are derived from seven
AOGCMs run under the SRES B1, B2, A2 and A1FI scenarios.
[WGII Table 16.2]
Regions
2010–2039
2040–2069
2070–2099
Mediterranean
-35.6 to +55.1
-52.6 to +38.3
-61.0 to +6.2
Caribbean
-14.2 to +13.7
-36.3 to +34.2
-49.3 to +28.9
Indian Ocean
-5.4 to +6.0
-6.9 to +12.4
-9.8 to +14.7
Northern Pacific
-6.3 to +9.1
-19.2 to +21.3
-2.7 to +25.8
Southern Pacific
-3. 9 to + 3.4
-8.23 to +6.7
-14.0 to +14.6
In the Pacific, a 10% reduction in average rainfall (by 2050)
would lead to a 20% reduction in the size of the freshwater lens
on Tarawa Atoll, Kiribati. Reduced rainfall coupled with sealevel rise would compound the risks to water supply reliability.
[WGII 16.4.1]
Many small islands have begun to invest in the implementation
of adaptation strategies, including desalination, to offset
current and projected water shortages. However, the impacts
of desalination plants themselves on environmental amenities
and the need to fully address environmental water requirements
have not been fully considered. [WGII 16.4.1]
Given the high visibility and impacts of hurricanes, droughts
have received less attention by researchers and planners,
although these may lead to increased withdrawals and potential
for saltwater intrusion into near-shore aquifers. In the Bahamas,
for instance, freshwater lenses are the only exploitable
groundwater resources. These lenses are affected periodically
by saline intrusions caused by over-pumping and excess
evapotranspiration. Groundwater in most cases is slow-moving
and, as a result, serious reductions in groundwater reserves
are slow to recover and may not be reversible; variability in
annual volumes of available water is generally not as extreme
as for surface water resources; and water quality degradation
and pollution have long-term effects and cannot quickly be
remedied. [WGII 16.4.1]
Some Island States such as Malta (MRAE, 2004) emphasise
potential economic sectors that will require adaptation,
including power generation, transport and waste management;
whereas agriculture and human health figure prominently in
communications from the Comoros (GDE, 2002), Vanuatu
(Republic of Vanuatu, 1999) and St. Vincent and the Grenadines
(NEAB, 2000). In these cases, sea-level rise is not seen as the
most critical issue, although it is in the low-lying atoll states
such as Kiribati, Tuvalu, Marshall Islands and the Maldives.
[WGII 16.4.2]
Section 5
Analysing regional aspects of climate change and water resources
5.8.2.2
Energy
Access to reliable and affordable energy is a vital element in
most small islands, where the high cost of energy is regarded
as a barrier to the goal of attaining sustainable development.
Some islands, such as Dominica in the Caribbean, rely on
hydropower for a significant part of their energy supply.
Research and development into energy efficiency and options
appropriate to small islands, such as solar and wind, could
help in both adaptation and mitigation strategies, while
enhancing the prospect of achieving sustainable growth.
[WGII 16.4.6, 16.4.7]
5.8.2.3
Health
Many small islands lie in tropical or sub-tropical zones with
weather conducive to the transmission of diseases such as
malaria, dengue, filariasis, schistosomiasis and food- and
water-borne diseases. The rates of occurrence of many of
these diseases are increasing in small islands for a number of
reasons, including poor public health practices, inadequate
infrastructure, poor waste-management practices, increasing
global travel, and changing climatic conditions (WHO, 2003).
In the Caribbean, the incidence of dengue fever increases during
warm years of ENSO cycles (Rawlins et al., 2005). Because
the greatest risk of dengue transmission is during annual wet
seasons, vector control programmes should target these periods
in order to reduce disease burdens. The incidence of diarrhoeal
diseases is associated with annual average temperature (Singh
et al., 2001) [WGII 8.2, 8.4], and negatively associated with
water availability in the Pacific (Singh et al., 2001). Therefore,
increasing temperatures and decreasing water availability due
to climate change may increase burdens of diarrhoeal and other
infectious diseases in some Small Island States. [WGII 16.4.5]
5.8.2.4
Agriculture
Projected impacts of climate change include extended periods
of drought and, on the other hand, loss of soil fertility and
degradation as a result of increased precipitation, both of which
will negatively impact on agriculture and food security. In its
study on the economic and social implications of climate change
and variability for selected Pacific islands, the World Bank
(2000) found that, in the absence of adaptation, a high island
such as Viti Levu, Fiji, could experience damages of US$23–
52 million per year by 2050, (equivalent to 2–3% of Fiji’s GDP
in 2002), while a group of low islands such as Tarawa, Kiribati,
could face damages of more than US$8–16 million a year
(equivalent to 17–18% of Kiribati’s GDP in 2002) under SRES
A2 and B2. On many Caribbean islands, reliance on agricultural
imports, which themselves include water used for production in
the countries of origin, constitute up to 50% of food supply.
[WGII 16.4.3]
5.8.2.5
Biodiversity
Burke et al. (2002) and Burke and Maidens (2004) indicate
that about 50% of the reefs in south-east Asia and 45% in the
Caribbean are classed in the high to very high risk category (see
also Graham et al, 2006). There are, however, significant local and
regional differences in the scale and type of threats to coral reefs
in both continental and small island situations. [WGII 16.4.4]
Both the terrestrial ecosystems of larger islands and coastal
ecosystems of most islands have been subjected to increasing
degradation and destruction in recent decades. For instance,
analysis of coral reef surveys over three decades has revealed that
coral cover across reefs in the Caribbean has declined by 80%
in just 30 years, largely as a result of pollution, sedimentation,
marine diseases and over-fishing (Gardner et al., 2003). Runoff
from land areas, together with direct input of freshwater through
heavy rain events, can have significant impacts on reef quality
and susceptibility to disease. [WGII 16.4.4]
5.8.3
Adaptation, vulnerability and sustainability
Sustainable development is often stated as an objective of
management strategies for small islands. Relatively little
work has explicitly considered what sustainable development
means for islands in the context of climate change (Kerr,
2005). It has long been known that the problems of small scale
and isolation, of specialised economies, and of the opposing
forces of globalisation and localisation, may mean that current
development in small islands becomes unsustainable in the long
term. [WGII 16.6]
Danger is associated with the narrowing of adaptation options
to expected impacts of climate change, under the uncertainty
of potential climate-driven physical impacts. Table 5.9
summarises the results of several scenario-based impact studies
for island environments from the present through to 2100, i.e.,
some impacts are already occurring. It provides the context for
other potential climate impacts that might exacerbate waterrelated stresses. Thresholds may originate from social as well
as environmental processes. Furthermore, the challenge is to
understand the adaptation strategies that have been adopted in
the past and the benefits and limits of these for future planning
and implementation. [WGII 16.5]
While there has been considerable progress in regional
projections of sea level since the TAR, such projections have
not been fully utilised in small islands because of the greater
uncertainty attached to their local manifestations, as opposed
to global projections. Reliable and credible projections based
on outputs at finer resolution, together with local data, are
needed to inform the development of reliable climate change
scenarios for small islands. These approaches could lead to
improved vulnerability assessments and the identification of
more appropriate adaptation options at the scale of islands and
across time-scales of climatic impacts. [WGII 16.7.1]
Vulnerability studies conducted for selected small islands
(Nurse et al., 2001) show that the costs of infrastructure and
settlement protection represent a significant proportion of
GDP, often well beyond the financial means of most Small
Island States; a problem not always shared by the islands of
continental countries. More recent studies have identified major
areas of adaptation, including water resources and watershed
management, reef conservation, agricultural and forest
management, conservation of biodiversity, energy security,
increased development of renewable energy and optimised
111
Section 5
Analysing regional aspects of climate change and water resources
* Numbers in bold relate to
the regions defined on the
map.
Table 5.9: Range of future impacts and vulnerabilities in small islands. [WGII Box 16.1]
Region* and System at
risk
Scenario and
Reference
Changed parameters
Impacts and vulnerability
•
The imbalance of species loss and replacement leads to an initial
loss in diversity. Northward expansion of dwarf-shrub and treedominated vegetation into areas rich in rare endemic species
results in their loss.
Large reduction in, or even a complete collapse of, the Icelandic
capelin stock leads to considerable negative impacts on most
commercial fish stocks, whales and seabirds.
1. Iceland and isolated
SRES A1 and B2
Arctic islands of Svalbard ACIA (2005)
and the Faroe Islands:
Marine ecosystem and
plant species
Projected rise in
temperature
2. High-latitude islands
(Faroe Islands): Plant
species
Scenario I/II:
temperature
increase/ decrease
by 2°C
Fosaa et al. (2004)
Changes in soil
temperature, snow
cover and growing
degree days
Own scenarios
Smith (2002)
Projected changes
in temperature and
precipitation
•
Changes will directly affect the indigenous biota. An even greater
threat is that a warmer climate will increase the ease with which
the islands can be invaded by alien species.
Alien plant invasion
under climatic and
disturbance scenarios
•
Climate change impacts are negligible in many simulated marine
ecosystems.
Invasion into island ecosystems becomes an increasing problem.
In the longer term, ecosystems will be dominated by exotic plants
irrespective of disturbance rates.
3. Sub-Antarctic Marion
Islands: Ecosystem
4. Mediterranean Basin five SRES A1FI and B1
islands: Ecosystems
Gritti et al. (2006)
5. Mediterranean: Migratory None
birds (pied flycatchers
(GLM/STATISTICA
– Ficedula hypoleuca)
model)
Sanz et al. (2003)
•
•
•
•
Temperature increase, •
changes in water levels
and vegetation index
Scenario I: Species most affected by warming are restricted to the
uppermost parts of mountains. For other species, the effect will
mainly be upward migration.
Scenario II: Species affected by cooling are those at lower
altitudes.
Some fitness components of pied flycatchers suffer from
climate change in two of the southernmost European breeding
populations, with adverse effects on the reproductive output of
pied flycatchers.
6. Pacific and
Mediterranean: Siam
weed (Chromolaena
odorata)
None
Increase in moisture,
(CLIMEX model)
cold, heat and dry
Kriticos et al. (2005) stress
•
•
Pacific islands at risk of invasion by Siam weed.
Mediterranean semi-arid and temperate climates predicted to be
unsuitable for invasion.
7. Pacific small islands:
Coastal erosion, water
resources and human
settlement
SRES A2 and B2
World Bank (2000)
•
Accelerated coastal erosion, saline intrusion into freshwater
lenses and increased flooding from the sea cause large effects
on human settlements.
Less rainfall coupled with accelerated sea-level rise compound
the threat to water resources; a 10% reduction in average rainfall
by 2050 is likely to correspond to a 20% reduction in the size of
the freshwater lens on Tarawa Atoll, Kiribati.
8. American Samoa; 15
other Pacific islands:
Mangroves
Sea-level rise
Projected rise
0.88 m to 2100
in sea level
Gilman et al. (2006)
•
50% loss of mangrove area in American Samoa; 12% reduction in
mangrove area in 15 other Pacific islands.
9. Caribbean (Bonaire,
Netherlands Antilles):
Beach erosion and sea
turtle nesting habitats
SRES A1, A1FI, B1, Projected rise in sea
A2, B2
level
Fish et al. (2005)
•
On average, up to 38% (±24% SD) of the total current beach could
be lost with a 0.5 m rise in sea level, with lower narrower beaches
being the most vulnerable, reducing turtle nesting habitat by onethird.
10. Caribbean (Bonaire,
iiBarbados): Tourism
None
Uyarra et al. (2005)
•
The beach-based tourism industry in Barbados and the marinediving-based ecotourism industry in Bonaire are both negatively
affected by climate change through beach erosion in Barbados
and coral bleaching in Bonaire.
112
Changes in
temperature and
rainfall, and sea-level
rise
Changes to marine
wildlife, health,
terrestrial features and
sea conditions
•
Section 5
Analysing regional aspects of climate change and water resources
energy consumption. A framework which considers current and
future community vulnerability and involves methodologies
integrating climate science, social science and communication,
provides the basis for building adaptive capacity. [WGII Box
16.7] This approach requires community members to identify
climate conditions relevant to them, and to assess present and
potential adaptive strategies. One such methodology was tested in
Samoa, and results from one village (Saoluafata: see Sutherland
et al., 2005). In this case, local residents identified several
adaptive measures including building a seawall, a water-drainage
system, water tanks, a ban on tree clearing, some relocation, and
renovation to existing infrastructure. [WGII 16.5]
The IPCC AR4 has identified several key areas and gaps that are
under-represented in contemporary research on the impacts of
climate change on small islands. [WGII 16.7] These include:
• the role of coastal ecosystems such as mangroves, coral
reefs and beaches in providing natural defences against
sea-level rise and storms;
• establishing the response of terrestrial upland and inland
ecosystems to changes in mean temperature and rainfall
and in temperature and rainfall extremes;
•
•
•
considering how commercial agriculture, forestry and
fisheries, as well as subsistence agriculture, artisanal fishing
and food security, will be impacted by the combination of
climate change and non-climate-related forces;
expanding knowledge of climate-sensitive diseases in
small islands through national and regional research – not
only for vector-borne diseases but for skin, respiratory and
water-borne diseases;
given the diversity of ‘island types’ and locations,
identifying the most vulnerable systems and sectors,
according to island types.
In contrast to the other regions in this assessment, there is
also an absence of reliable demographic and socio-economic
scenarios and projections for small islands. The result is that
future changes in socio-economic conditions on small islands
have not been well presented in the existing assessments. For
example, without either adaptation or mitigation, the impacts
of sea-level rise, more intense storms and other climate
change [WGII 6.3.2] will be substantial, suggesting that some
islands and low-lying areas may become unliveable by 2100.
[WGII 16.5]
113
6
Climate change mitigation measures
and water
Climate change mitigation measures and water
Section 6
6.1 Introduction
The relationship between climate change mitigation measures
and water is a reciprocal one. Mitigation measures can influence
water resources and their management, and it is important to
realise this when developing and evaluating mitigation options.
On the other hand, water management policies and measures
can have an influence on greenhouse gas (GHG) emissions
and, thus, on the respective sectoral mitigation measures;
interventions in the water system might be counter-productive
when evaluated in terms of climate change mitigation.
The issue of mitigation is addressed in the IPCC WGIII AR4
(Mitigation), where the following seven sectors were discussed:
energy supply, transportation and its infrastructure, residential
and commercial buildings, industry, agriculture, forestry, and
waste management. Since water issues were not the focus of
that volume, only general interrelations with climate change
mitigation were mentioned, most of them being qualitative.
However, other IPCC reports, such as the TAR, also contain
information on this issue.
Sector-specific mitigation measures can have various effects on
water, which are explained in the sections below (see also Table
6.1). Numbers in parentheses in the titles of the sub-sections
correspond to the practices or sector-specific mitigation options
described in Table 6.1.
6.2 Sector-specific mitigation
6.2.1
Carbon dioxide capture and storage (CCS)
iiiiiiiiiiiiiiii(refer to (1) in Table 6.1)
Carbon dioxide (CO2) capture and storage (CCS) is a process
consisting of the separation of CO2 from industrial and energyrelated sources, transport to a storage location and long-term
isolation from the atmosphere. The injection of CO2 into the
pore space and fractures of a permeable formation can displace
in situ fluid, or the CO2 may dissolve in or mix with the
fluid or react with the mineral grains, or there may be some
combination of these processes. As CO2 migrates through the
formation, some of it will dissolve into the formation water.
Once CO2 is dissolved in the formation fluid, it is transported
by the regional groundwater flow. Leakage of CO2 from leaking
injection wells, abandoned wells, and leakage across faults
and ineffective confining layers could potentially degrade the
quality of groundwater; and the release of CO2 back into the
atmosphere could also create local health and safety concerns.
[CCS SPM, 5.ES]
It is important to note that, at this point, there is no complete
insight into the practicality, consequences or unintended
consequences of this carbon sequestration concept. Avoiding
or mitigating the impacts will require careful site selection,
effective regulatory oversight, an appropriate monitoring
programme, and implementation of remediation methods to
stop or control CO2 releases. [CCS 5.ES, 5.2].
6.2.2
Bio-energy crops (2)
Bio-energy produces mitigation benefits by displacing fossilfuel use. [LULUCF 4.5.1] However, large-scale bio-fuel
production raises questions on several issues including fertiliser
and pesticide requirements, nutrient cycling, energy balances,
biodiversity impacts, hydrology and erosion, conflicts with
food production, and the level of financial subsidies required.
[LULUCF 4.5.1] The energy production and GHG mitigation
potentials of dedicated energy crops depends on the availability
of land, which must also meet demands for food as well as for
nature protection, sustainable management of soils and water
reserves, and other sustainability criteria. Various studies
have arrived at differing figures for the potential contribution
of biomass to future global energy supplies, ranging from
below 100 EJ/yr to above 400 EJ/yr in 2050 (Hoogwijk, 2004;
Hoogwijk et al., 2005; Sims et al., 2006). Smeets et al. (2007)
indicate that the ultimate technical potential for energy cropping
on current agricultural land, with projected technological
progress in agriculture and livestock, could deliver over 800 EJ/
yr without jeopardising the world’s food supply. Differences
between studies are largely attributable to uncertainty in land
availability, energy crop yields, and assumptions about changes
in agricultural efficiency. Those with the largest projected
potential assume that not only degraded/surplus lands are used,
but also land currently used for food production, including
pasture land (as did Smeets et al., 2007). [WGIII 8.4.4.2]
Agricultural practices for mitigation of GHGs could, in some
cases, intensify water use, thereby reducing streamflow or
groundwater reserves (Unkovich, 2003; Dias de Oliveira et al.,
2005). For instance, high-productivity, evergreen, deep-rooted
bio-energy plantations generally have a higher water use than the
land cover they replace (Berndes and Börjesson, 2002; Jackson
et al., 2005). Some practices may affect water quality through
enhanced leaching of pesticides and nutrients (Machado and
Silva, 2001; Freibauer et al., 2004). [WGIII 8.8]
Agricultural mitigation practices that divert products to
alternative uses (e.g., bio-energy crops) may induce the
conversion of forests to cropland elsewhere. Conversely,
increasing productivity on existing croplands may ‘spare’ some
forest or grasslands (West and Marland, 2003; Balmford et al.,
2005; Mooney et al., 2005). The net effect of such trade-offs on
biodiversity and other ecosystem services has not yet been fully
quantified (Huston and Marland, 2003; Green et al., 2005).
[WGIII 8.8]
If bio-energy plantations are appropriately located, designed
and managed, they may reduce nutrient leaching and soil
erosion and generate additional environmental services such
as soil carbon accumulation, improved soil fertility, and the
removal of cadmium and other heavy metals from soils or
wastes. They may also increase nutrient recirculation, aid in the
117
Section 6
Climate change mitigation measures and water
Table 6.1: Influence of sector-specific mitigation options (or their consequences) on water quality, quantity and level. Positive
effects on water are indicated with [+]; negative effects with [−]; and uncertain effects with [?]. Numbers in round brackets
refer to the Notes, and also to the sub-section numbers in Section 6.2.
Water aspect
Energy
Buildings
Industry
Agriculture
Forests
Waste
CCS(1) [?]
Wastewater
treatment(12) [-]
Biomass
electricity(3) [-/?]
Land-use
change and
management
(7)
[+/-]
Cropland
management
(water)(8) [+/-]
Afforestation
(sinks)(10) [+]
Solid waste
management;
Wastewater
treatment(12) [+/-]
Afforestation
(10)
[+/-]
Avoided/ reduced
deforestation
(11)
[+]
Wastewater
treatment(12) [+]
Quality
Chemical/
biological
CCS(1) [?]
Bio-fuels(2) [+/-]
Geothermal
energy(5) [-]
Unconventional
oil(13) [-]
Temperature
Biomass
electricity(3) [+]
Cropland
management
(reduced tillage)
(9)
[+/-]
Quantity
Availability/
demand
Hydropower(4)
[+/-]
Unconventional
oil(13) [-]
Geothermal
energy(5) [-]
Energy use in
buildings(6) [+/-]
Land-use
change and
management
(7)
[+/-]
Cropland
management
(water)(8) [-]
Flow/runoff/
recharge
Bio-fuels(2) [+/-]
Hydropower
(4)
[+/-]
Cropland
management
(reduced tillage)
(9)
[+]
Surface water
Hydropower
(4)
[+/-]
Land-use
change and
management
(7)
[+/-]
Groundwater
Geothermal
energy(5) [-]
Land-use
change and
management
(7)
[+/-]
Water level
Afforestation(10) [-]
Notes:
(1) Carbon capture and storage (CCS) underground poses potential risks to groundwater quality; deep-sea storage (below 3,000 m water depth and a few hundred metres
of sediment) seems to be the safest option.
(2) Expanding bio-energy crops and forests may cause negative impacts such as increased water demand, contamination of underground water and promotion of landuse changes, leading to indirect effects on water resources; and/or positive impacts through reduced nutrient leaching, soil erosion, runoff and downstream siltation.
(3) Biomass electricity: in general, a higher contribution of renewable energy (as compared to fossil-fuel power plants) means a reduction of the discharge of cooling
iiiiiiiiiwater to the surface water.
(4) Environmental impact and multiple benefits of hydropower need to be taken into account for any given development; they could be either positive or negative.
(5) Geothermal energy use might result in pollution, subsidence and, in some cases, a claim on available water resources.
(6) Energy use in the building sector can be reduced by different approaches and measures, with positive and negative impacts.
(7) Land-use change and management can influence surface water and groundwater quality (e.g., through enhanced or reduced leaching of nutrients and pesticides) and
the (local) hydrological cycle (e.g., a higher water use).
(8) Agricultural practices for mitigation can have both positive and negative effects on conservation of water and on its quality.
(9) Reduced tillage promotes increased water-use efficiency.
(10) Afforestation generally improves groundwater quality and reduces soil erosion. It influences both catchment and regional hydrological cycles (a smoothed hydrograph,
thus reducing runoff and flooding). It generally gives better watershed protection, but at the expense of surface water yield and aquifer recharge, which may be critical
in semi-arid and arid regions.
(11) Stopping/slowing deforestation and forest degradation conserve water resources and prevent flooding, reduce run-off, control erosion and reduce siltation of rivers.
(12) The various waste management and wastewater control and treatment technologies can both reduce GHG emissions and have positive effects on the environment,
but they may cause water pollution in case of improperly designed or managed facilities.
(13) As conventional oil supplies become scarce and extraction costs increase, unconventional liquid fuels will become more economically attractive, but this is offset by
greater environmental costs (a high water demand; sanitation costs).
118
Climate change mitigation measures and water
Section 6
treatment of nutrient-rich wastewater and sludge, and provide
habitats for biodiversity in the agricultural landscape (Berndes
and Börjesson, 2002; Berndes et al., 2004; Börjesson and
Berndes, 2006). [WGIII 8.8] In the case of forest plantations
for obtaining bio-fuels, negative environmental impacts are
avoidable through good project design. Environmental benefits
include, among others, reduced soil degradation, water runoff,
and downstream siltation and capture of polluting agricultural
runoff. [LULUCF Fact Sheet 4.21]
6.2.3
Biomass electricity (3)
Non-hydro renewable energy supply technologies, particularly
solar, wind, geothermal and biomass, are currently small
overall contributors to global heat and electricity supply, but
are increasing most rapidly, albeit from a low base. Growth of
biomass electricity is restricted due to cost, as well as social and
environmental barriers. [WGIII 4.ES] For the particular case
of biomass electricity, any volumes of biomass needed above
those available from agricultural and forest residues [WGIII
Chapters 8 and 9] will need to be purpose-grown, so could be
constrained by land and water availability. There is considerable
uncertainty, but there should be sufficient production possible
in all regions to meet the additional generation from bio-energy
of 432 TWh/yr by 2030, as projected in this analysis. [WGIII
4.4.4] In general, the substitution of fossil fuels by biomass in
electricity generation will reduce the amount of cooling water
discharged to surface water streams.
6.2.4
Hydropower (4)
Renewable energy systems such as hydro-electricity can
contribute to the security of energy supply and protection of the
environment . However, construction of hydro-electric power
plants may also cause ecological impacts on existing river
ecosystems and fisheries, induced by changes in flow regime
(the hydrograph) and evaporative water losses (in the case of
dam-based power-houses). Also social disruption may be an
impact. Finally, water availability for shipping (water depth)
may cause problems. Positive effects are flow regulation, flood
control, and availability of water for irrigation during dry
seasons. Furthermore, hydropower does not require water for
cooling (as in the case of thermal power plants) or, as in the
case of bio-fuels, for growth. About 75% of water reservoirs
in the world were built for irrigation, flood control and urban
water supply schemes, and many could have small hydropower
generation retrofits added without additional environmental
impacts. [WGIII 4.3.3]
Large (>10 MW) hydro-electricity systems accounted for over
2,800 TWh of consumer energy in 2004 and provided 16% of
global electricity (90% of renewable electricity). Hydro projects
under construction could increase the share of hydro-electricity
by about 4.5% on completion and new projects could be
deployed to provide a further 6,000 TWh/yr or more of electricity
economically, mainly in developing countries. Repowering
existing plants with more powerful and efficient turbine designs
can be cost-effective whatever the plant scale. [WGIII 4.3.3.1]
Small (<10 MW) and micro (<1 MW) hydropower systems,
usually run-of-river schemes, have provided electricity to many
rural communities in developing countries such as Nepal. Their
present generation output is uncertain, with predictions ranging
from 4 TWh/yr to 9% of total hydropower output at 250 TWh/
yr. The global technical potential of small and micro-hydro is
around 150–200 GW, with many unexploited resource sites
available. [WGIII 4.3.3.1]
The many benefits of hydro-electricity, including irrigation and
water supply resource creation, rapid response to grid demand
fluctuations due to peaks or intermittent renewables, recreational
lakes, and flood control, as well as the negative aspects, need to
be evaluated for any given development. [WGIII 4.3.3.1]
6.2.5
Geothermal energy (5)
Geothermal resources have long been used for direct heat
extraction for district urban heating, industrial processing,
domestic water and space heating, leisure and balneotherapy
applications. [WGIII 4.3.3.4]
Geothermal fields of natural steam are rare, most being a
mixture of steam and hot water requiring single or double flash
systems to separate out the hot water, which can then be used
in binary plants or for direct heating. Re-injection of the fluids
maintains a constant pressure in the reservoir, hence increasing
the field’s life and reducing concerns about environmental
impacts. [WGIII 4.3.3.4]
Sustainability concerns relating to land subsidence, heat
extraction rates exceeding natural replenishment (Bromley
and Currie, 2003), chemical pollution of waterways (e.g., with
arsenic), and associated CO2 emissions have resulted in some
geothermal power plant permits being declined. This could be
partly overcome by re-injection techniques. Deeper drilling
technology could help to develop widely abundant hot dry rocks
where water is injected into artificially fractured rocks and heat
extracted as steam. However, at the same time, this means a
claim on available water resources. [WGIII 4.3.3.4]
6.2.6
Energy use in buildings (6)
Evaporative cooling, as a mitigation measure, means substantial
savings in annual cooling energy use for residences. However,
this type of cooling places an extra pressure on available water
resources. Cooling energy use in buildings can be reduced by
different measures, for example reducing the cooling load by
building shape and orientation. Reducing this energy means,
in the case of using water for cooling, a lower water demand.
[WGIII 6.4.4]
6.2.7
Land-use change and management (7)
According to IPCC Good Practice Guidance for LULUCF,
there are six possible broad land-use categories: forest land,
cropland, grassland, wetlands, settlements, and other. Changes
in land use (e.g., conversion of cropland to grassland) may
119
Section 6
Climate change mitigation measures and water
result in net changes in carbon stocks and in different impacts
on water resources. For land-use changes other than land
converted to forest (as discussed in Section 6.2.10), previous
IPCC documents contain very few references to their impacts
on water resources. Wetland restoration, one of the main
mitigation practices in agriculture [WGIII 8.4.1.3], results
in the improvement of water quality and decreased flooding.
[LULUCF Table 4.10] Set-aside, another mitigation practice
identified by WGIII, may have positive impacts on both water
conservation and water quality. [WGIII Table 8.12]
Land management practices implemented for climate change
mitigation may also have different impacts on water resources.
Many of the practices advocated for soil carbon conservation –
reduced tillage, more vegetative cover, greater use of perennial
crops – also prevent erosion, yielding possible benefits for
improved water and air quality (Cole et al., 1993). These
practices may also have other potential adverse effects, at least
in some regions or conditions. Possible effects include enhanced
contamination of groundwater with nutrients or pesticides via
leaching under reduced tillage (Cole et al., 1993; Isensee and
Sadeghi, 1996). These possible negative effects, however,
have not been widely confirmed or quantified, and the extent
to which they may offset the environmental benefits of carbon
sequestration is uncertain. [WGIII TAR 4.4.2]
The group of practices known as agriculture intensification (Lal
et al., 1999; Bationo et al., 2000; Resck et al., 2000; Swarup
et al., 2000), including those that enhance production and the
input of plant-derived residues to soil (crop rotations, reduced
bare fallow, cover crops, high-yielding varieties, integrated
pest management, adequate fertilisation, organic amendments,
irrigation, water-table management, site-specific management,
and others), has numerous ancillary benefits, the most important
of which is the increase and maintenance of food production.
Environmental benefits can include erosion control, water
conservation, improved water quality, and reduced siltation of
reservoirs and waterways. Soil and water quality is adversely
affected by the indiscriminate use of agriculture inputs and
irrigation water. [LULUCF Fact Sheet 4.1]
Nutrient management to achieve efficient use of fertilisers
has positive impacts on water quality. [WGIII Table 8.12] In
addition, practices that reduce N2O emission often improve the
efficiency of nitrogen use from these and other sources (e.g.,
manures), thereby also reducing GHG emissions from fertiliser
manufacture and avoiding deleterious effects on water and air
quality from nitrogen pollutants (Dalal et al., 2003; Paustian
et al., 2004; Oenema et al., 2005; Olesen et al., 2006). [WGIII
8.8]
Agro-forestry systems (plantation of trees in cropland) can
provide multiple benefits including energy to rural communities
with synergies between sustainable development and GHG
mitigation. [LULUCF 4.5.1] However, agro-forestry may have
negative impacts on water conservation. [WGIII Table 8.12]
120
6.2.8
Cropland management (water) (8)
Agricultural practices which promote the mitigation of
greenhouse gases can have both negative and positive effects
on the conservation of water, and on its quality. Where the
measures promote water-use efficiency (e.g., reduced tillage),
they provide potential benefits. But in some cases, the practices
could intensify water use, thereby reducing streamflow or
groundwater reserves (Unkovich, 2003; Dias de Oliveira et
al., 2005). Rice management has generally positive impacts on
water quality through a reduction in the amount of chemical
pollutants in drainage water. [WGIII Table 8.12]
6.2.9
Cropland management (reduced tillage) (9)
Conservation tillage is a generic term that includes a wide
range of tillage practices, including chisel plough, ridge till,
strip till, mulch till and no till (CTIC, 1998). Adoption of
conservation tillage has numerous ancillary benefits. Important
among these benefits are the control of water and wind erosion,
water conservation, increased water-holding capacity, reduced
compaction, increased soil resilience to chemical inputs,
increased soil and air quality, enhanced soil biodiversity,
reduced energy use, improved water quality, reduced siltation
of reservoirs and waterways, and possible double-cropping.
In some areas (e.g., Australia), increased leaching from
greater water retention with conservation tillage can cause
downslope salinisation. [LULUCF Fact Sheet 4.3] Important
secondary benefits of conservation tillage adoption include soil
erosion reduction, improvements in water quality, increased
fuel efficiency, and increases in crop productivity. [LULUCF
4.4.2.4] Tillage/residue management has positive impacts on
water conservation. [WGIII Table 8.12]
6.2.10
Afforestation or reforestation (10)
Forests, generally, are expected to use more water (the sum
of transpiration and evaporation of water intercepted by tree
canopies) than crops, grass, or natural short vegetation. This
effect, occurring in lands that are subjected to afforestation or
reforestation, may be related to increased interception loss,
especially where the canopy is wet for a large proportion of the
year (Calder, 1990) or, in drier regions, to the development of
more massive root systems, which allow water extraction and
use during prolonged dry seasons. [LULUCF 2.5.1.1.4]
Interception losses are greatest from forests that have large leaf
areas throughout the year. Thus, such losses tend to be greater
for evergreen forests than for deciduous forests (Hibbert, 1967;
Schulze, 1982) and may be expected to be larger for fast-growing
forests with high rates of carbon storage than for slow-growing
forests. Consequently, afforestation with fast-growing conifers
on non-forest land commonly decreases the flow of water from
catchments and can cause water shortages during droughts
(Hibbert, 1967; Swank and Douglass, 1974). Vincent (1995),
for example, found that establishing high-water-demanding
Climate change mitigation measures and water
Section 6
species of pines to restore degraded Thai watersheds markedly
reduced dry season streamflows relative to the original
deciduous forests. Although forests lower average flows, they
may reduce peak flows and increase flows during dry seasons
because forested lands tend to have better infiltration capacity
and a high capacity to retain water (Jones and Grant, 1996).
Forests also play an important role in improving water quality.
[LULUCF 2.5.1.1.4]
In many regions of the world where forests grow above shallow
saline water tables, decreased water use following deforestation
can cause water tables to rise, bringing salt to the surface (Morris
and Thomson, 1983). In such situations, high water use by trees
(e.g., through afforestation or reforestation) can be of benefit
(Schofield, 1992). [LULUCF 2.5.1.1.4]
In the dry tropics, forest plantations often use more water than
short vegetation because trees can access water at greater depth
and evaporate more intercepted water. Newly planted forests
can use more water (by transpiration and interception) than
the annual rainfall, by mining stored water (Greenwood et al.,
1985). Extensive afforestation or reforestation in the dry tropics
can therefore have a serious impact on supplies of groundwater
and river flows. It is less clear, however, whether replacing
natural forests with plantations, even with exotic species,
increases water use in the tropics when there is no change
in rooting depth or stomatal behaviour of the tree species. In
the dry zone of India, water use by Eucalyptus plantations is
similar to that of indigenous dry deciduous forest: both forest
types essentially utilise all the annual rainfall (Calder, 1992).
[LULUCF 2.5.1.1.4]
Afforestation and reforestation, like forest protection, may also
have beneficial hydrological effects. After afforestation in wet
areas, the amount of direct runoff initially decreases rapidly,
then gradually becomes constant, and baseflow increases
slowly as stand age increases towards maturity (Fukushima,
1987; Kobayashi, 1987), suggesting that reforestation and
afforestation help to reduce flooding and enhance water
conservation. In water-limited areas, afforestation, especially
plantations of species with high water demand, can cause a
significant reduction in streamflow, affecting the inhabitants of
the basin (Le Maitre and Versfeld, 1997), and reducing water
flow to other ecosystems and rivers, thus affecting aquifers
and recharge (Jackson et al., 2005). In addition, some possible
changes in soil properties are largely driven by changes in
hydrology. The hydrological benefits of afforestation may need
to be evaluated individually for each site. [WGIII TAR 4.4.1]
Positive socio-economic benefits, such as wealth or job
creation, must be balanced by the loss of welfare resulting from
reductions in available water, grazing, natural resources, and
agricultural land. Afforestation of previously eroded or otherwise
degraded land may have a net positive environmental impact; in
catchments where the water yield is large or is not heavily used,
streamflow reduction may not be critical. [LULUCF 4.7.2.4]
6.2.11
Avoided/reduced deforestation (11)
Stopping or slowing deforestation and forest degradation (loss
of carbon density) and sustainable management of forests may
significantly contribute to avoided emissions, may conserve
water resources and prevent flooding, reduce runoff, control
erosion, reduce siltation of rivers, and protect fisheries and
investments in hydro-electric power facilities; and at the same
time preserve biodiversity (Parrotta, 2002). [WGIII 9.7.2]
Preserving forests conserves water resources and prevents
flooding. For example, the flood damage in Central America
following Hurricane Mitch was apparently enhanced by the
loss of forest cover. By reducing runoff, forests control erosion
and salinity. Consequently, maintaining forest cover can
reduce siltation of rivers, protecting fisheries and investment
in hydro-electric power facilities (Chomitz and Kumari, 1996).
[WGIII TAR 4.4.1]
Deforestation and degradation of upland catchments can
disrupt hydrological systems, replacing year-round water flows
in downstream areas with flood and drought regimes (Myers,
1997). Although there are often synergies between increased
carbon storage through afforestation, reforestation and
deforestation (ARD) activities and other desirable associated
impacts, no general rules can be applied; impacts must be
assessed individually for each specific case. Associated impacts
can often be significant, and the overall desirability of specific
ARD activities can be greatly affected by their associated
impacts. [LULUCF 3.6.2]
6.2.12
Solid waste management; wastewater
iiiiiiiiiiiiiiiiitreatment (12)
Controlled landfill (with or without gas recovery and utilisation)
controls and reduces GHG emissions but may have negative
impacts on water quality in the case of improperly managed sites.
This also holds for aerobic biological treatment (composting)
and anaerobic biological treatment (anaerobic digestion).
Recycling, reuse and waste minimisation can be negative for
waste scavenging from open dump sites, with water pollution
as a potential consequence. [WGIII Table 10.7]
When efficiently applied, wastewater transport and treatment
technologies reduce or eliminate GHG generation and
emissions. In addition, wastewater management promotes water
conservation by preventing pollution from untreated discharges
to surface water, groundwater, soils, and coastal zones, thus
reducing the volume of pollutants, and requiring a smaller
volume of water to be treated. [WGIII 10.4.6]
Treated wastewater can either be reused or discharged, but reuse
is the most desirable option for agricultural and horticultural
irrigation, fish aquaculture, artificial recharge of aquifers, or
industrial applications. [WGIII 10.4.6]
121
Section 6
Climate change mitigation measures and water
6.2.13
Unconventional oil (13)
As conventional oil supplies become scarce and extraction
costs increase, unconventional liquid fuels will become more
economically attractive, although this is offset by greater
environmental costs (Williams et al., 2006). Mining and
upgrading of oil shale and oil sands requires the availability of
abundant water. Technologies for recovering tar sands include
open cast (surface) mining, where the deposits are shallow
enough, or injection of steam into wells in situ to reduce the
viscosity of the oil prior to extraction. The mining process uses
about four litres of water to produce one litre of oil but produces
a refinable product. The in situ process uses about two litres
of water to one litre of oil, but the very heavy product needs
cleaning and diluting (usually with naphtha) at the refinery or
needs to be sent to an upgrader to yield syncrude at an energy
efficiency of around 75% (NEB, 2006). The energy efficiency
of oil sand upgrading is around 75%. Mining of oil sands leaves
behind large quantities of pollutants and areas of disturbed land.
[WGIII 4.3.1.4]
6.3 Effects of water management policies
iiiiiiiand measures on GHG emissions and
iiiiiiimitigation
As shown in the previous section, climate change mitigation
practices in various sectors may have an impact on water
resources. Conversely, water management policies and
measures can have an influence on GHG emissions associated
with different sectors, and thus on their respective mitigation
measures (Table 6.2).
6.3.1
Hydro dams (1)
About 75% of water reservoirs in the world were built for
irrigation, flood control and urban water supply schemes.
Greenhouse gas emissions vary with reservoir location, power
density (power capacity per area flooded), flow rate, and
whether the plant is dam-based or run-of-river type. Recently,
the greenhouse gas footprint of hydropower reservoirs has
been questioned. Some reservoirs have been shown to absorb
carbon dioxide at their surface, but most emit small amounts
of GHGs as water conveys carbon in the natural carbon cycle.
High emissions of methane have been recorded at shallow,
plateau-type tropical reservoirs where the natural carbon cycle
is most productive, while deep-water reservoirs exhibit lower
emissions. Methane from natural floodplains and wetlands
may be suppressed if they are inundated by a new reservoir,
since methane is oxidised as it rises through the water column.
Methane formation in freshwater involves by-product carbon
compounds (phenolic and humic acids) that effectively
sequester the carbon involved. For shallow tropical reservoirs,
further research is needed to establish the extent to which these
may increase methane emissions. [WGIII 4.3.3.1]
122
The emission of greenhouse gases from reservoirs due to rotting
vegetation and carbon inflows from the catchment is a recently
identified ecosystem impact of dams. This challenges the
conventional wisdom that hydropower produces only positive
atmospheric effects (e.g., reductions in emissions of CO2 and
nitrous oxides), when compared with conventional power
generation sources (World Commission on Dams, 2000).
Lifecycle assessments of hydropower projects available at
the time of the AR4 showed low overall net greenhouse gas
emissions. Given that measuring the incremental anthropogenicrelated emissions from freshwater reservoirs remains uncertain,
the UNFCCC Executive Board has excluded large hydro projects
with significant water storage from its Clean Development
Mechanism (CDM). [WGIII 4.3.3.1]
6.3.2
Irrigation (2)
About 18% of the world’s croplands now receive supplementary
water through irrigation (Millennium Ecosystem Assessment,
2005a, b). Expanding this area (where water reserves allow), or
using more effective irrigation measures, can enhance carbon
storage in soils through enhanced yields and residue returns
(Follett, 2001; Lal, 2004). However, some of these gains may be
offset by carbon dioxide from energy used to deliver the water
(Schlesinger, 1999; Mosier et al., 2005) or from N2O emissions
from higher moisture and fertiliser nitrogen inputs (Liebig et
al., 2005), though the latter effect has not been widely measured
[WGIII 8.4.1.1.d]. The expansion of wetland rice area may also
cause increased methane emissions from soils (Yan et al., 2003).
[WGIII 8.4.1.1.e]
6.3.3
Residue return (3)
Weed competition for water is an important cause of crop
failure or decreases in crop yields worldwide. Advances in weed
control methods and farm machinery now allow many crops
to be grown with minimal tillage (reduced tillage) or without
tillage (no-till). These practices, which result in the maintenance
of crop residues on the soil surface, thus avoiding water losses
by evaporation, are now being used increasingly throughout the
world (e.g., Cerri et al., 2004). Since soil disturbance tends to
stimulate soil carbon losses through enhanced decomposition
and erosion (Madari et al., 2005), reduced- or no-till agriculture
often results in soil carbon gain, though not always (West
and Post, 2002; Alvarez, 2005; Gregorich et al., 2005; Ogle
et al., 2005). Adopting reduced- or no-till may also affect
emissions of N2O, but the net effects are inconsistent and not
well quantified globally (Cassman et al., 2003; Smith and
Conen, 2004; Helgason et al., 2005; Li et al., 2005). The effect
of reduced tillage on N2O emissions may depend on soil and
climatic conditions: in some areas reduced tillage promotes
N2O emissions; elsewhere it may reduce emissions or have
no measurable influence (Marland et al., 2001). Furthermore,
no-tillage systems can reduce carbon dioxide emissions from
Climate change mitigation measures and water
Section 6
Table 6.2: Influence of water management on sectoral GHG emissions. Increased GHG emissions are indicated with [−],
(because this implies a negative impact) and reduced GHG emissions with [+]. Numbers in round brackets refer to the Notes,
and also to the sub-section numbers in Section 6.3.
Sector
Quality
Chemical/
biological
Energy
Quantity
Temperature
Average demand
Geothermal
energy(7) [+]
Hydro dams(1) [+/-]
Irrigation(2) [-]
Geothermal energy(7) [+]
Desalinisation(6) [-]
Agriculture
Waste
Water level
Hydro dams(1) [-]
Soil moisture
Surface water
Ground water
Hydro dams
(1)
[+/-]
Irrigation(2) [+/-]
Residue return(3) [+]
Drainage of
cropland(4) [+/-]
Wastewater
treatment(5) [+/-]
Notes:
(1) Hydropower does not require fossil fuel and is an important source of renewable energy. However, recently the GHG footprint of hydropower reservoirs has been
questioned. In particular, methane is a problem.
(2) Applying more effective irrigation measures can enhance carbon storage in soils through enhanced yields and residue returns, but some of these gains may be offset
by CO2 emissions from the energy used to deliver the water. Irrigation may also induce additional CH4 and N2O emissions, depending on case-specific
circumstances.
(3) Residue returned to the field, to improve water-holding capacity, will sequester carbon through both increased crop productivity and reduced soil respiration.
(4) Drainage of agricultural lands in humid regions can promote productivity (and hence soil carbon) and perhaps also suppress N2O emissions by improving aeration.
Any nitrogen lost through drainage, however, may be susceptible to loss as N2O.
(5) Depending on the design and management of facilities (wastewater treatment and treatment purification technologies), more or less CH4 and N2O emissions – the major
GHG emissions from wastewater – can be emitted during all stages from source to disposal; however, in practice, most emissions occur upstream of treatment.
(6) Desalinisation requires the use of energy, and thus generates GHG emissions.
(7) Using geothermal energy for heating purposes does not generate GHG emissions, as is the case with other methods of energy production.
energy use (Marland et al., 2003; Koga et al., 2006). Systems
that retain crop residues also tend to increase soil carbon because
these residues are the precursors for soil organic matter, the
main store of carbon in soil. Avoiding the burning of residues
(e.g., mechanising the harvest of sugarcane, eliminating the
need for pre-harvest burning; Cerri et al., 2004), also avoids
emissions of aerosols and GHGs generated from fire, although
carbon dioxide emissions from fuel use may increase. [WGIII
8.4.1.1.c]
6.3.4
Drainage of cropland (4)
Drainage of croplands in humid regions can promote productivity
(and hence soil carbon) and perhaps also suppress N2O emissions
by improving aeration (Monteny et al., 2006). Any nitrogen lost
through drainage, however, may be susceptible to loss as N2O
(Reay et al., 2003). [WGIII 8.4.1.1.d]
6.3.5
Wastewater treatment (5)
For landfill CH4, the largest GHG emission source from the
waste sector, emissions continue several decades after waste
disposal, and thus estimation of emission trends requires models
which include temporal trends. CH4 is also emitted during
wastewater transport, sewage treatment processes, and leakage
from anaerobic digestion of waste or wastewater sludges.
The major sources of N2O are human sewage and wastewater
treatment. [WGIII 10.3.1]
The methane emissions from wastewater alone are expected
to increase by almost 50% between 1990 and 2020, especially
in the rapidly developing countries of eastern and southern
Asia. Estimates of global N2O emissions from wastewater are
incomplete and based only on human sewage treatment, but
these indicate an increase of 25% between 1990 and 2020. It
is important to emphasise, however, that these are businessas-usual scenarios, and actual emissions could be much lower
if additional measures were put in place. Future reductions in
emissions from the waste sector will partially depend on the
post-2012 availability of Kyoto mechanisms such as the CDM.
[WGIII 10.3.1]
In developing countries, due to rapid population growth and
urbanisation without concurrent development of wastewater
infrastructure, CH4 and N2O emissions from wastewater are
generally higher than in developed countries. This can be seen
by examining the 1990 estimated methane and N2O emissions
and projected trends to 2020 from wastewater and human
sewage. [WGIII 10.3.3]
Although current GHG emissions from wastewater are lower
than emissions from waste, it is recognised that there are
substantial emissions that are not quantified by current estimates,
especially from septic tanks, latrines, and uncontrolled discharges
in developing countries. Decentralised ‘natural’ treatment
processes and septic tanks in developing countries may result
in relatively large emissions of methane and N2O, particularly
123
Climate change mitigation measures and water
in China, India and Indonesia. Open sewers or informally
ponded wastewaters in developing countries often result in
uncontrolled discharges to rivers and lakes, causing rapidly
increasing wastewater volumes going along with economic
development. On the other hand, low-water-use toilets (3–
5 litres) and ecological sanitation approaches (including
ecological toilets) where nutrients are safely recycled into
productive agriculture and the environment, are being used
in Mexico, Zimbabwe, China and Sweden. These could also
be applied in many developing and developed countries,
especially where there are water shortages, irregular water
supplies, or where additional measures for the conservation
of water resources are needed. All of these measures also
encourage smaller wastewater treatment plants with reduced
nutrient loads and proportionally lower GHG emissions.
[WGIII 10.6.2] All in all, the quantity of wastewater
collected and treated is increasing in many countries in order
to maintain and improve potable water quality, as well for
other public health and environmental protection benefits.
Concurrently, GHG emissions from wastewater will decrease
relative to future increases in wastewater collection and
treatment. [WGIII 10.6.2]
6.3.6
Desalinisation (6)
In water-scarce regions, water supply may take place (partly)
by desalinisation of saline water. Such a process requires
energy and this implies the generation of GHG emissions in
the case of fossil-fuel utilisation. [WGII 3.3.2]
6.3.7
Geothermal energy (7)
Using geothermal energy for heating purposes does not
generate GHG emissions, as is the case with other methods
of energy generation (see also Section 6.2.5).
124
Section 6
6.4 Potential water resource conflicts
iiiiiiibetween adaptation and mitigation
Possible conflicts between adaptation and mitigation might arise
over water resources. The few studies that exist (e.g., Dang et al.,
2003) indicate that the repercussions from mitigation for adaptation
and vice versa are mostly marginal at the global level, although they
may be significant at the regional scale. In regions where climate
change will trigger significant shifts in the hydrological regime, but
where hydropower potentials are still available, this would increase
the competition for water, especially if climate change adaptation
efforts in various sectors are implemented (such as competition for
surface water resources between irrigation, to cope with climate
change impacts in agriculture, increased demand for drinking water,
and increased demand for cooling water for the power sector). This
confirms the importance of integrated land and water management
strategies for river basins, to ensure the optimal allocation of scarce
natural resources (land, water). Also, both mitigation and adaptation
have to be evaluated at the same time, with explicit trade-offs, in
order to optimise economic investments while fostering sustainable
development.[WGII 18.8, 18.4.3]
Several studies confirm potential clashes between water supply,
flood control, hydropower and minimum streamflow (required for
ecological and water quality purposes) under changing climatic and
hydrological conditions (Christensen et al., 2004; Van Rheenen et
al., 2004). [WGII 18.4.3]
Adaptation to changing hydrological regimes and water
availability will also require continuous additional energy input.
In water-scarce regions, the increasing reuse of wastewater and
the associated treatment, deep-well pumping, and especially largescale desalination, would increase energy use in the water sector
(Boutkan and Stikker, 2004), thus generating GHG emissions,
unless ‘clean energy’ options are used to generate the necessary
energy input. [WGII 18.4.3]
7
Implications for policy and
sustainable development
Implications for policy and sustainable development
Section 7
Climate change poses a major conceptual challenge to water
managers, water resource users (e.g., in agriculture) as well
as to policymakers in general, as it is no longer appropriate
to assume that past climatic and hydrological conditions will
continue into the future. Water resources management clearly
impacts on many other policy areas (e.g., energy, health, food
security, nature conservation). Thus, the appraisal of adaptation
and mitigation options needs to be conducted across multiple
water-dependent sectors.
Substantial changes have been observed over recent decades
in many water-related variables, but clear formal attribution
of the observed changes to natural or anthropogenic causes
is not generally possible at present. Projections of future
precipitation, soil moisture and runoff at regional scales are
subject to substantial uncertainty. In many regions, models
do not agree on the sign of projected change. However, some
robust patterns are found across climate model projections.
Increases in precipitation (and river flow) are very likely at high
latitudes and in some wet tropics (including populous areas in
east and south-east Asia), and decreases are very likely over
much of the mid-latitudes and dry tropics [WGII Figure 3.4].
Interpretation and quantification of uncertainties has recently
improved, and new methods (e.g., ensemble-based approaches)
are being developed for their characterisation [WGII 3.4,
3.5]. Nevertheless, quantitative projections of changes in
precipitation, river flows and water levels at the river-basin
scale remain uncertain, so that planning decisions involving
climate change must be made in the context of this uncertainty.
[WGII TS, 3.3.1, 3.4]
Effective adaptation to climate change occurs across temporal
and spatial scales, including incorporation of lessons from
responses to climate variability into longer-term vulnerability
reduction efforts and within governance mechanisms from
communities and watersheds to international agreements.
Continued investment in adaptation in response to historical
experience alone, rather than projected future conditions
that will include both variability and change, is likely to
increase the vulnerability of many sectors to climate change.
[WGII TS, 14.5]
•
•
•
•
•
•
•
7.1 Implications for policy by sector
Water resource management
•
Catchments that are dominated by seasonal snow cover
already experience earlier peak flows in spring, and this
shift is expected to continue under a warmer climate. At
lower altitudes, winter precipitation will increasingly
be in the form of rainfall instead of snowfall. In many
mountain areas, e.g., in the tropical Andes and many
Asian mountains, where glaciers provide the main runoff
during pronounced dry seasons, water volumes stored in
glaciers and snow cover are projected to decline. Runoff
during warm and dry seasons is enhanced while glaciers
are shrinking, but will dramatically drop after they have
disappeared. [WGII 3.4.1]
•
Drought-affected areas are likely to increase; and extreme
precipitation events, which are very likely to increase in
frequency and intensity, will augment flood risk. Up to
20% of the world’s population live in river basins that are
likely to be affected by increased flood hazard by the 2080s
in the course of climate change. [WGII 3.4.3]
Semi-arid and arid areas are particularly exposed to the
impacts of climate change on freshwater. Many of these
areas (e.g., the Mediterranean Basin, western USA,
southern Africa, north-eastern Brazil, southern and eastern
Australia) will suffer a decrease in water resources due to
climate change. [WGII Box TS.5, 3.4, 3.7] Efforts to offset
declining surface water availability due to increasing
precipitation variability will be hampered by the fact that
groundwater recharge is projected to decrease considerably
in some water-stressed regions [WGII 3.4.2], exacerbated
by the increased water demand. [WGII 3.5.1]
Higher water temperatures, increased precipitation
intensity and longer periods of low flows exacerbate many
forms of water pollution, with impacts on ecosystems,
human health, and water system reliability and operating
costs. [WGII 3.2, 3.4.4, 3.4.5]
Areas in which runoff is projected to decline will face
a reduction in the value of services provided by water
resources. The beneficial impacts of increased annual
runoff in some other areas will be tempered by the negative
effects of increased precipitation variability and seasonal
runoff shifts on water supply, water quality and flood risks.
[WGII 3.4, 3.5]
At the global level, the negative impacts of climate change
on freshwater systems outweigh the benefits. [WGII 3.4,
3.5]
Adverse effects of climate on freshwater systems
aggravate the impacts of other stresses, such as population
growth, land-use change and urbanisation. [WGII 3.3.2,
3.5] Globally, water demand will grow in the coming
decades, primarily due to population growth and increased
affluence. [WGII 3.5.1]
Climate change affects the function and operation of existing
water infrastructure as well as water management practices.
Current water management practices are very likely to be
inadequate to reduce the negative impacts of climate change
on water-supply reliability, flood risk, health, energy and
aquatic ecosystems. [WGII TS, 3.4, 3.5, 3.6]
Adaptation procedures and risk management practices for
the water sector are being developed in some countries
and regions (e.g., the Caribbean, Canada, Australia, the
Netherlands, the UK, the USA and Germany) that recognise
the uncertainty of projected hydrological changes, but
evaluation criteria on effectiveness need to be developed.
[WGII 3.6]
Ecosystems
•
The resilience of many ecosystems and their ability
to adapt naturally is likely to be exceeded by 2100 by
an unprecedented combination of change in climate,
associated disturbances (e.g., flooding, drought, wildfire)
and other global change drivers (e.g., land-use change,
127
Implications for policy and sustainable development
Section 7
pollution, over-exploitation of resources). [WGII TS]
Greater rainfall variability is likely to compromise wetlands
through shifts in the timing, duration and depth of water
levels. [WGII 4.4.8]
Of all ecosystems, freshwater ecosystems will have the
highest proportion of species threatened with extinction
due to climate change. [WGII 4.4.8]
Current conservation practices are generally poorly
prepared to adapt to the projected changes in water
resources during the coming decades. [WGII 4.ES]
Effective adaptation responses that will conserve
biodiversity and other ecosystem services are likely to
be costly to implement, but unless conservation water
needs are factored into adaptation strategies, many natural
ecosystems and the species they support will decline.
[WGII 4.ES, 4.4.11, Table 4.1, 4.6.1, 4.6.2]
Industry, settlement and society
•
Infrastructure, such as urban water supply systems, are
vulnerable, especially in coastal areas, to sea-level rise and
reduced regional precipitation. [WGII 7.4.3, 7.5]
•
Projected increases in extreme precipitation events have
important implications for infrastructure: design of storm
drainage, road culverts and bridges, levees and flood
control works, including sizing of flood control detention
reservoirs. [WGII 7.4.3.2]
•
Planning regulations can be used to prevent development
in high-flood-risk zones (e.g., on floodplains), including
housing, industrial development and siting of landfill sites
etc. [WGII 7.6]
•
Infrastructure development, with its long lead times and
large investments, would benefit from incorporating
climate-change information. [WGII 14.5.3, Figure 14.3]
Agriculture, forests
•
An increased frequency of droughts and floods negatively
affects crop yields and livestock, with impacts that are
both larger and earlier than predicted by using changes
in mean variables alone. [WGII 5.4.1, 5.4.2] Increases in
the frequency of droughts and floods will have a negative
effect on local production, especially in subsistence sectors
at low latitudes. [WGII SPM]
•
Impacts of climate change on irrigation water requirements
may be large. [WGII 5.4] New water storages, both surface
and underground, can alleviate water shortages but are not
always feasible. [WGII 5.5.2]
•
Farmers may be able to partially adjust by changing
cultivars and/or planting dates for annual crops and by
adopting other strategies. The potential for higher water
needs should be considered in the design of new irrigation
supply systems and in the rehabilitation of old systems.
[WGII 5.5.1]
•
Measures to combat water scarcity, such as the reuse of
wastewater for agriculture, need to be carefully managed
to avoid negative impacts on occupational health and food
safety. [WGII 8.6.4]
•
Unilateral measures to address water shortages due to
climate change can lead to competition for water resources.
International and regional approaches are required in order
to develop joint solutions. [WGII 5.7]
Sanitation and human health
•
Climate-change-induced effects on water pose a threat
to human health through changes in water quality and
availability. Although access to water supplies and
sanitation is determined primarily by non-climate factors, in
some populations climate change is expected to exacerbate
problems of access at the household level. [WGII 8.2.5]
•
Appropriate disaster planning and preparedness need to be
developed in order to address the increased risk of flooding
due to climate change and to reduce impacts on health and
health systems. [WGII 8.2.2]
•
•
•
•
Coastal systems and low-lying areas
•
Sea-level rise will extend areas of salinisation of
groundwater and estuaries, resulting in a decrease in
freshwater availability. [WGII 3.2, 3.4.2]
•
Settlements in low-lying coastal areas that have low
adaptive capacity and/or high exposure are at increased
risk from floods and sea-level rise. Such areas include
river deltas, especially Asian megadeltas (e.g., the GangesBrahmaputra in Bangladesh and west Bengal), and lowlying coastal urban areas, especially areas prone to natural
or human-induced subsidence and tropical storm landfall
(e.g., New Orleans, Shanghai). [WGII 6.3, 6.4]
128
Climate information needs
Progress in understanding the climate impact on the water
cycle depends on improved data availability. Relatively short
hydrometric records can underestimate the full extent of
natural variability. Comprehensive monitoring of water-related
variables, in terms of both quantity and quality, supports decision
making and is a prerequisite for the adaptive management
required under conditions of climate change. [WGII 3.8]
7.2 The main water-related projected
iiiiiiiimpacts by regions
Africa
•
The impacts of climate change in Africa are likely to
be greatest where they co-occur with a range of other
stresses (population growth; unequal access to resources;
inadequate access to water and sanitation [WGII 9.4.1];
food insecurity [WGII 9.6]; poor health systems [WGII
9.2.2, 9.4.3]). These stresses and climate change will
increase the vulnerabilities of many people in Africa.
[WGII 9.4]
•
An increase of 5–8% (60–90 million ha) of arid and semiarid land in Africa is projected by the 2080s under a range
of climate change scenarios. [WGII 9.4.4]
•
Declining agricultural yields are likely due to drought and
land degradation, especially in marginal areas. Mixed rainfed systems in the Sahel will be greatly affected by climate
Implications for policy and sustainable development
Section 7
•
•
change. Mixed rain-fed and highland perennial systems in
the Great Lakes region and in other parts of East Africa
will also be severely affected. [WGII 9.4.4, Box TS.6]
Current water stress in Africa is likely to be increased by
climate change, but water governance and water-basin
management must also be considered in future assessments
of water stress in Africa. Increases in runoff in East Africa
(and increased risk of flood events) and decreases in
runoff (and increased risk of drought) in other areas (e.g.,
southern Africa) are projected by the 2050s. [WGII 9.4.1,
9.4.2, 9.4.8]
Any changes in the primary production of large lakes
will have important impacts on local food supplies. Lake
Tanganyika currently provides 25–40% of animal protein
intake for the surrounding populations, and climate
change is likely to reduce primary production and possible
fish yields by roughly 30% [WGII 9.4.5, 3.4.7, 5.4.5].
The interaction of poor human management decisions,
including over-fishing, is likely to further reduce fish yields
from lakes. [WGII 9.2.2, Box TS.6]
Asia
•
The per capita availability of freshwater in India is expected
to drop from around 1,820 m3 currently to below 1,000 m3
by 2025 in response to the combined effects of population
growth and climate change. [WGII 10.4.2.3]
•
More intense rain and more frequent flash floods during
the monsoon would result in a higher proportion of runoff
and a reduction in the proportion reaching the groundwater.
[WGII 10.4.2]
•
Agricultural irrigation demand in arid and semi-arid
regions of east Asia is expected to increase by 10% for an
increase in temperature of 1°C. [WGII 10.4.1]
•
Coastal areas, especially heavily populated Asian
megadelta regions, will be at greatest risk due to increased
flooding from the sea and, in some megadeltas, flooding
from rivers. [WGII 6.4, 10.4.3]
•
Changes in snow and glacier melt, as well as rising
snowlines in the Himalayas, will affect seasonal
variation in runoff, causing water shortages during dry
summer months. One-quarter of China’s population and
hundreds of millions in India will be affected (Stern,
2007). [WGII 3.4.1, 10.4.2.1]
Australia and New Zealand
•
Ongoing water security problems are very likely to increase
in southern and eastern Australia (e.g., a 0–45% decline in
runoff in Victoria by 2030 and a 10–25% reduction in river
flow in Australia’s Murray-Darling Basin by 2050) and,
in New Zealand, in Northland and some eastern regions.
[WGII 11.4.1]
•
Risks to major infrastructure are likely to increase due
to climate change. Design criteria for extreme events
are very likely to be exceeded more frequently by 2030.
Risks include failure of floodplain levees and urban
drainage systems, and flooding of coastal towns near
rivers. [WGII 11.ES, 11.4.5, 11.4.7]
•
Production from agriculture and forestry by 2030 is
projected to decline over much of southern and eastern
Australia, and over parts of eastern New Zealand, due
to, among other things, increased drought. However, in
New Zealand, initial benefits are projected in western and
southern areas and close to major rivers, with increased
rainfall. [WGII 11.4]
Europe
•
The probability of an extreme winter precipitation
exceeding two standard deviations above normal is
expected to increase by up to a factor of five in parts of the
UK and northern Europe by the 2080s with a doubling of
CO2. [WGII 12.3.1]
•
By the 2070s, annual runoff is projected to increase in
northern Europe, and decrease by up to 36% in southern
Europe, with summer low flows reduced by up to 80%
under the IS92a scenario. [WGII 12.4.1, T12.2]
•
The percentage of river-basin area in the severe water
stress category (withdrawal:availability ratio greater than
0.4) is expected to increase from 19% today to 34–36% by
the 2070s. [WGII 12.4.1]
•
The number of additional people living in water-stressed
watersheds in 17 countries in western Europe is likely
to increase by 16–44 million (HadCM3 climate model
results) by the 2080s. [WGII 12.4.1]
•
By the 2070s, hydropower potential for the whole of
Europe is expected to decline by 6%, with strong regional
variations from a 20–50% decrease in the Mediterranean
region to a 15–30% increase in northern and eastern
Europe. [WGII 12.4.8]
•
Small mountain glaciers in different regions will disappear,
while larger glaciers will suffer a volume reduction
between 30% and 70% by 2050 under a range of emissions
scenarios, with concomitant reductions in discharge in
spring and summer. [WGII 12.4.3]
Latin America
•
Any future reductions in rainfall in arid and semi-arid
regions of Argentina, Chile and Brazil are likely to lead to
severe water shortages. [WGII 13.4.3]
•
Due to climate change and population growth, the number
of people living in water-stressed watersheds is projected
to reach 37–66 million by the 2020s (compared to an
estimate of 56 million without climate change) for the
SRES A2 scenario. [WGII 13.4.3]
•
Areas in Latin America with severe water stress include
eastern Central America, the plains, Motagua Valley and
Pacific slopes of Guatemala, eastern and western regions
of El Salvador, the central valley and Pacific region of
Costa Rica, the northern, central and western intermontane
regions of Honduras, and the peninsula of Azuero in
Panama). In these areas, water supply and hydro-electricity
generation could be seriously affected by climate change.
[WGII 13.4.3]
•
Glacier shrinkage is expected to increase dry-season
water shortages under a warming climate, with adverse
129
Section 7
Implications for policy and sustainable development
consequences for water availability and hydropower
generation in Bolivia, Peru, Colombia and Ecuador.
Flood risk is expected to grow during the wet season.
[WGII 13.2.4, 13.4.3]
North America
•
Projected warming in the western mountains by the mid21st century is very likely to cause large decreases in
snowpack, earlier snowmelt, more winter rain events,
increased peak winter flows and flooding, and reduced
summer flows. [WGII 14.4.1]
•
Reduced water supplies coupled with increases in demand
are likely to exacerbate competition for over-allocated
water resources. [WGII 14.2.1, Box 14.2]
•
Moderate climate change in the early decades of the
century is projected to increase aggregate yields of rainfed agriculture by 5–20%, but with important variability
among regions. Major challenges are projected for crops
that are near the warm end of their suitable range or which
depend on highly utilised water resources. [WGII 14.4.4]
•
Vulnerability to climate change is likely to be concentrated
in specific groups and regions, including indigenous
peoples and others dependent on narrow resource bases,
and the poor and elderly in cities. [WGII 14.2.6, 14.4.6]
Polar regions
•
Northern Hemisphere permafrost extent is likely to decrease
by 20–35% by 2050. The depth of seasonal thawing is
projected to increase by 15–25% in most areas by 2050, and
by 50% or more in northernmost locations under the full range
of SRES scenarios. [WGII 15.3.4] In the Arctic, disruption
of ecosystems is projected as a result. [WGII 15.4.1]
•
Further reductions in lake and river ice cover are expected,
affecting thermal structures, the quality/quantity of
under-ice habitats and, in the Arctic, the timing and
severity of ice jamming and related flooding. Freshwater
warming is expected to influence the productivity
and distribution of aquatic species, especially fish,
leading to changes in fish stock, and reductions in
those species that prefer colder waters. [WGII 15.4.1]
•
Increases in the frequency and severity of flooding, erosion
and destruction of permafrost threaten Arctic communities,
industrial infrastructure and water supply. [WGII 15.4.6]
Small islands
•
There is strong evidence that, under most climate change
scenarios, water resources in small islands are likely to be
seriously compromised [WGII 16.ES]. Most small islands
have a limited water supply, and water resources in these
islands are especially vulnerable to future changes and
distribution of rainfall. Many islands in the Caribbean are
likely to experience increased water stress as a result of
climate change. Under all SRES scenarios, reduced rainfall
in summer is projected for this region, so that it is unlikely
that demand would be met during low rainfall periods.
Increased rainfall in winter is unlikely to compensate, due
to the lack of storage and high runoff during storm events.
[WGII 16.4.1]
130
•
•
A reduction in average rainfall would lead to a reduction
in the size of the freshwater lens. In the Pacific, a 10%
reduction in average rainfall (by 2050) would lead to a
20% reduction in the size of the freshwater lens on Tarawa
Atoll, Kiribati. Reduced rainfall, coupled with increased
withdrawals, sea-level rise and attendant salt-water
intrusion, would compound this threat. [WGII 16.4.1]
Several small-island countries (e.g., Barbados, Maldives,
Seychelles and Tuvalu) have begun to invest in the
implementation of adaptation strategies, including
desalination, to offset current and projected water
shortages. [WGII 16.4.1]
7.3 Implications for climate mitigation
iiiiiiipolicy
Implementing important mitigation options such as
afforestation, hydropower and bio-fuels may have positive and
negative impacts on freshwater resources, depending on sitespecific situations. Therefore, site-specific joint evaluation and
optimisation of (the effectiveness of) mitigation measures and
water-related impacts are needed.
Expansion of irrigated areas and dam-based hydro-electric
power generation can lead to reduced effectiveness of associated
mitigation potential. In the case of irrigation, CO2 emissions
due to energy consumption for pumping water and to methane
emissions in rice fields may partly offset any mitigation effects.
Freshwater reservoirs for hydropower generation may produce
some greenhouse gas emissions, so that an overall case-specific
evaluation of the ultimate greenhouse gas budget is needed.
[WGIII 4.3.3.1, 8.4.1.1]
7.4 Implications for sustainable
iiiiiiidevelopment
Low-income countries and regions are expected to remain
vulnerable over the medium term, with fewer options than highincome countries for adapting to climate change. Therefore,
adaptation strategies should be designed in the context of
development, environment and health policies. Many of the
options that can be used to reduce future vulnerability are of
value in adapting to current climate and can be used to achieve
other environmental and social objectives.
In many regions of the globe, climate change impacts on
freshwater resources may affect sustainable development
and put at risk the reduction of poverty and child mortality
(Table 7.1). It is very likely that negative impacts of increased
frequency and severity of floods and droughts on sustainable
development cannot be avoided [WGII 3.7]. However, aside
from major extreme events, climate change is seldom the
main factor exerting stress on sustainability. The significance
of climate change lies in its interactions with other sources of
change and stress, and its impacts should be considered in such
a multi-cause context. [WGII 7.1.3, 7.2, 7.4]
Implications for policy and sustainable development
Section 7
Table 7.1: Potential contribution of the water sector to attain the Millennium Development Goals. [WGII Table 3.6]
Goals
Direct relation to water
Indirect relation to water
Goal 1:
Eradicate extreme
poverty and hunger
Water is a factor in many production activities (e.g., agriculture,
animal husbandry, cottage industries)
Sustainable production of fish, tree crops and other food brought
together in common property resources
Reduced ecosystem degradation improves
local-level sustainable development
Reduced urban hunger by means of cheaper
food from more reliable water supplies
Goal 2:
Achieve universal
education
Improved school attendance through improved
health and reduced water-carrying burdens,
especially for girls
Goal 3:
Promote gender
equity
and empower
women
Development of gender-sensitive water management programmes
Goal 4:
Reduce child
mortality
Improved access to drinking water of more adequate quantity and
better quality, and improved sanitation, to reduce the main factors of
morbidity and mortality in young children
Goal 6:
Combat HIV/AIDS,
malaria and
other diseases
Improved access to water and sanitation supports HIV/AIDS-affected
households and may improve the impact of health care programmes
Better water management reduces mosquito habitats and the risk of
malaria transmission
Goal 7:
Ensure
environmental
sustainability
Improved water management reduces water consumption and
recycles nutrients and organics
Actions to ensure access to improved and, possibly, productive ecosanitation for poor households
Actions to improve water supply and sanitation services for poor
communities
Actions to reduce wastewater discharge and improve environmental
health in slum areas
Reduce time wasted and health burdens
through improved water service, leading
to more time for income-earning and more
balanced gender roles
Develop operation, maintenance, and cost
recovery system to ensure sustainability of
service delivery
131
8
Gaps in knowledge and suggestions
for further work
Gaps in knowledge and suggestions for further work
Section 8
There is abundant evidence from observational records and
climate projections that freshwater resources are vulnerable
and have the potential to be strongly impacted by climate
change. However, the ability to quantify future changes in
hydrological variables, and their impacts on systems and
sectors, is limited by uncertainty at all stages of the assessment
process. Uncertainty comes from the range of socio-economic
development scenarios, the range of climate model projections
for a given scenario, the downscaling of climate effects to
local/regional scales, impacts assessments, and feedbacks from
adaptation and mitigation activities. Limitations in observations
and understanding restrict our current ability to reduce these
uncertainties. Decision making needs to operate in the context
of this uncertainty. Robust methods to assess risks based on
these uncertainties are at an early stage of development.
Capacity for mitigation of climate change and adaptation to its
impacts is limited by the availability and economic viability of
appropriate technologies and robust collaborative processes for
decision making among multiple stakeholders and management
criteria. Knowledge of the costs and benefits (including
avoided damages) of specific options is scarce. Management
strategies that adapt as the climate changes require an adequate
observational network to inform them. There is limited
understanding of the legal and institutional frameworks and
demand-side statistics necessary for mainstreaming adaptation
into development plans to reduce water-related vulnerabilities,
and of appropriate channels for financial flows into the water
sector for adaptation investment.
This section notes a number of key gaps in knowledge related
to these needs.
8.1 Observational needs
Better observational data and data access are necessary
to improve understanding of ongoing changes, to better
constrain model projections, and are a prerequisite for adaptive
management required under conditions of climate change.
Progress in knowledge depends on improved data availability.
Shrinkage of some observational networks is occurring.
Relatively short records may not reveal the full extent of
natural variability and confound detection studies, while longterm reconstruction can place recent trends and extremes in a
broader context. Major gaps in observations of climate change
related to freshwater and hydrological cycles were identified as
follows [WGI TS.6; WGII 3.8]:
• Difficulties in the measurement of precipitation remain an
area of concern in quantifying global and regional trends.
Precipitation measurements over oceans (from satellites)
are still in the development phase. There is a need to ensure
ongoing satellite monitoring, and the development of
reliable statistics for inferred precipitation. [WGI 3.3.2.5]
• Many hydrometeorological variables e.g., streamflow, soil
moisture and actual evapotranspiration, are inadequately
measured. Potential evapotranspiration is generally
•
•
•
•
•
•
calculated from parameters such as solar radiation, relative
humidity and wind speed. Records are often very short, and
available for only a few regions, which impedes complete
analysis of changes in droughts. [WGI 3.3.3, 3.3.4]
There may be opportunities for river flow data rescue
in some regions. Where no observations are available,
the construction of new observing networks should be
considered. [WGI 3.3.4]
Groundwater is not well monitored, and the processes of
groundwater depletion and recharge are not well modelled
in many regions. [WGI 3.3.4]
Monitoring data are needed on water quality, water use and
sediment transport.
Snow, ice and frozen ground inventories are incomplete.
Monitoring of changes is unevenly distributed in both space
and time. There is a general lack of data from the Southern
Hemisphere. [WGI TS 6.2, 4.2.2, 4.3]
More information is needed on plant evapotranspiration
responses to the combined effects of rising atmospheric
CO2, rising temperature and rising atmospheric water vapour
concentration, in order to better understand the relationship
between the direct effects of atmospheric CO2 enrichment
and changes in the hydrological cycle. [WGI 7.2]
Quality assurance, homogenisation of data sets, and intercalibration of methods and procedures could be important
whenever different agencies, countries etc., maintain
monitoring within one region or catchment.
8.2 Understanding climate projections
iiiiiiiand their impacts
8.2.1
Understanding and projecting climate
change
Major uncertainties in understanding and modelling changes in
climate relating to the hydrological cycle include the following
[SYR; WGI TS.6]:
• Changes in a number of radiative drivers of climate are not
fully quantified and understood (e.g., aerosols and their
effects on cloud properties, methane, ozone, stratospheric
water vapour, land-use change, past solar variations).
• Confidence in attributing some observed climate change
phenomena to anthropogenic or natural processes is limited
by uncertainties in radiative forcing, as well as by uncertainty
in processes and observations. Attribution becomes more
difficult at smaller spatial and temporal scales, and there
is less confidence in understanding precipitation changes
than there is for temperature. There are very few attribution
studies for changes in extreme events.
• Uncertainty in modelling some modes of climate variability,
and of the distribution of precipitation between heavy and
light events, remains large. In many regions, projections of
changes in mean precipitation also vary widely between
models, even in the sign of the change. It is necessary to
improve understanding of the sources of uncertainty.
• In many regions where fine spatial scales in climate are
135
Section 8
Gaps in knowledge and suggestions for further work
generated by topography, there is insufficient information
on how climate change will be expressed at these scales.
• Climate models remain limited by the spatial resolution and
ensemble size that can be achieved with present computer
resources, by the need to include some additional processes,
and by large uncertainties in the modelling of certain
feedbacks (e.g., from clouds and the carbon cycle).
• Limited knowledge of ice sheet and ice shelf processes
leads to unquantified uncertainties in projections of future
ice sheet mass balance, leading in turn to uncertainty in sealevel rise projections.
8.2.2
Water-related impacts [WGII 3.5.1, 3.8]
• Because of the uncertainties involved, probabilistic
approaches are required to enable water managers
to undertake analyses of risk under climate change.
Techniques are being developed to construct probability
distributions of specified outcomes. Further development
of this research, and of techniques to communicate the
results, as well as their application to the user community,
are required.
• Further work on detection and attribution of present-day
hydrological changes is required; in particular, changes in
water resources and in the occurrence of extreme events.
As part of this effort, the development of indicators of
climate change impacts on freshwater, and operational
systems to monitor them, are required.
• There remains a scale mismatch between the large-scale
climatic models and the catchment scale – the most
important scale for water management. Higher-resolution
climate models, with better land-surface properties and
interactions, are therefore required to obtain information
of more relevance to water management. Statistical and
physical downscaling can contribute.
• Most of the impact studies of climate change on water
stress in countries assess demand and supply on an annual
basis. Analysis at the monthly or higher temporal resolution
scale is desirable, since changes in seasonal patterns and
the probability of extreme events may offset the positive
effect of increased availability of water resources.
• The impact of climate change on snow, ice and frozen
ground as sensitive storage variables in the water cycle is
highly non-linear and more physically- and process-oriented
modelling, as well as specific atmospheric downscaling, is
required. There is a lack of detailed knowledge of runoff
changes as caused by changing glaciers, snow cover, rain–
snow transition, and frozen ground in different climate
regions.
• Methods need to be improved that allow the assessment of
the impacts of changing climate variability on freshwater
resources. In particular, there is a need to develop localscale data sets and simple climate-linked computerised
watershed models that would allow water managers
to assess impacts and to evaluate the functioning and
resilience of their systems, given the range of uncertainty
surrounding future climate projections.
136
• Feedbacks between land use and climate change (including
vegetation change and anthropogenic activity such as
irrigation and reservoir construction) should be analysed
more extensively; e.g., by coupled climate and land-use
modelling.
• Improved assessment of the water-related consequences
of different climate policies and development pathways is
needed.
• Climate change impacts on water quality are poorly
understood for both developing and developed countries,
particularly with respect to the impact of extreme events.
• Relatively few results are available on the socio-economic
aspects of climate change impacts related to water resources,
including climate change impacts on water demand.
• Impacts of climate change on aquatic ecosystems (not only
temperatures, but also altered flow regimes, water levels
and ice cover) are not understood adequately.
• Despite its significance, groundwater has received little
attention in climate change impact assessment compared to
surface water resources.
8.3 Adaptation and mitigation
• Water resources management clearly impacts on many other
policy areas (e.g., energy projections, land use, food security
and nature conservation). Adequate tools are not available to
facilitate the appraisal of adaptation and mitigation options
across multiple water-dependent sectors, including the
adoption of water-efficient technologies and practices.
• In the absence of reliable projections of future changes in
hydrological variables, adaptation processes and methods
which can be usefully implemented in the absence of
accurate projections, such as improved water-use efficiency
and water-demand management, offer no-regrets options to
cope with climate change. [WGII 3.8]
• Biodiversity. Identification of water resources needs for
maintaining environmental values and services, especially
related to deltaic ecosystems, wetlands and adequate
instream flows.
• Carbon capture and storage: Better understanding is needed
of leakage processes, because of potential degradation of
groundwater quality. This requires an enhanced ability to
monitor and verify the behaviour of geologically stored
CO2. [CCS, TS, Chapter 10]
• Hydropower/dam construction: An integrated approach
is needed, given the diversity of interests (flood control,
hydropower, irrigation, urban water supply, ecosystems,
fisheries and navigation), to arrive at sustainable solutions.
Methane emissions have to be estimated. Also, the net
effect on the carbon-budget in the affected region has to be
evaluated.
• Bio-energy: Insight is required into the water demand, and
its consequences, of large-scale plantations of commercial
bio-energy crops. [WGIII 4.3.3.3]
• Agriculture: Net effects of more effective irrigation on the
GHG budget need to be better understood (higher carbon
Section 8
storage in soils through enhanced yields and residue returns
and its offset by CO2 emissions from energy systems to
deliver the water, or by N2O emissions from higher moisture
and fertiliser inputs). [WGIII 8.4.1.1]
• Forestry: Better understanding of the effects of
massive afforestation on the processes forming the
hydrological cycle, such as rainfall, evapotranspiration,
Gaps in knowledge and suggestions for further work
runoff, infiltration and groundwater recharge is needed.
[WGIII 9.7.3]
• Wastewater and water reuse: Greater insight is needed
into emissions from decentralised treatment processes and
uncontrolled wastewater discharges in developing countries.
The impact of properly reusing water on mitigation and
adaptation strategies needs to be understood and quantified.
137
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163
Appendix I: Climate model descriptions
Model
Originating group
Resolution (lat/lon)
Reference for description of
model (see below)
CGCM1
Canadian Centre for Climate
Modelling and Analysis, Canada
Atmospheric component: ~3.7° x 3.7°
Ocean component: ~1.8° x 1.8°
Flato et al., 2000
HadCM2
Met Office Hadley Centre, UK
2.5° x 3.75°
Johns et al., 1997
HadCM3
Met Office Hadley Centre, UK
2.5° x 3.75°
Gordon et al., 2000
Pope et al., 2000
RegCM2
National Center for Atmospheric
Research, USA
~50 km
Giorgi et al., 1993a, b
ECHAM4
(with OPYC3)
Max Planck Institut für
Meteorologie (MPI) and the
Deutsches Klimarechenzentrum
(DKRZ), Germany
~2.8° x 2.8°
Roeckner et al., 1996
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165
Appendix II: Glossary
Editor: Jean Palutikof (United Kingdom)
Co-Editors: Clair Hanson (United Kingdom), Bryson Bates (Australia)
This Glossary is based on the glossaries published in the IPCC Fourth Assessment Report.
The italics used have the following meaning: Glossary word reference; Glossary secondary reference (i.e., terms which
are either contained in a glossary of the IPCC Working Group contributions to the AR4, or defined within the text of an
entry of this glossary).
A.
Abrupt climate change
The nonlinearity of the climate system may lead to abrupt
climate change, sometimes called rapid climate change, abrupt
events or even surprises. The term abrupt often refers to time
scales faster than the typical time scale of the responsible
forcing. However, not all abrupt climate changes need be
externally forced. Some possible abrupt events that have been
proposed include a dramatic reorganisation of the thermohaline
circulation, rapid deglaciation and massive melting of permafrost
or increases in soil respiration leading to fast changes in the
carbon cycle. Others may be truly unexpected, resulting from a
strong, rapidly changing, forcing of a non-linear system.
Active layer
The layer of ground that is subject to annual thawing and
freezing in areas underlain by permafrost.
Adaptation
Initiatives and measures to reduce the vulnerability of natural
and human systems against actual or expected climate change
effects. Various types of adaptation exist, e.g., anticipatory and
reactive, private and public, and autonomous and planned.
Examples are raising river or coastal dikes, the substitution of
more temperature-shock resistant plants for sensitive ones, etc.
Adaptive capacity
The whole of capabilities, resources and institutions of a country
or region to implement effective adaptation measures.
Aerosols
A collection of airborne solid or liquid particles, with a typical
size between 0.01 and 10 micrometre (a millionth of a metre)
that reside in the atmosphere for at least several hours. Aerosols
may be of either natural or anthropogenic origin. Aerosols may
influence climate in several ways: directly through scattering
and absorbing radiation, and indirectly through acting as cloud
condensation nuclei or modifying the optical properties and
lifetime of clouds.
Afforestation
Planting of new forests on lands that historically have not
contained forests (for at least 50 years). For a discussion of the
term forest and related terms such as afforestation, reforestation,
and deforestation see the IPCC Report on Land Use, Land-Use
Change and Forestry (IPCC, 2000).
Albedo
The fraction of solar radiation reflected by a surface or object,
often expressed as a percentage. Snow-covered surfaces have a
high albedo, the surface albedo of soils ranges from high to low,
and vegetation-covered surfaces and oceans have a low albedo.
The Earth’s planetary albedo varies mainly through varying
cloudiness, snow, ice, leaf area and land cover changes.
Algal bloom
A reproductive explosion of algae in a lake, river, or ocean.
Alpine
The biogeographic zone made up of slopes above the tree line,
characterised by the presence of rosette-forming herbaceous
plants and low shrubby slow-growing woody plants.
Annex I countries
The group of countries included in Annex I (as amended in
1998) to the United Nations Framework Convention on Climate
Change (UNFCCC), including all the OECD countries in the
year 1990 and countries with economies in transition. Under
Articles 4.2 (a) and 4.2 (b) of the Convention, Annex I countries
committed themselves specifically to the aim of returning
individually or jointly to their 1990 levels of greenhouse gas
emissions by the year 2000. By default, the other countries are
referred to as non-Annex I countries.
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Appendix II: Glossary
Annex II countries
The group of countries included in Annex II to the United Nations
Framework Convention on Climate Change (UNFCCC),
including all OECD countries in the year 1990. Under Article
4.2 (g) of the Convention, these countries are expected to
provide financial resources to assist developing countries
to comply with their obligations, such as preparing national
reports. Annex II countries are also expected to promote the
transfer of environmentally sound technologies to developing
countries.
Annex B countries
The countries included in Annex B to the Kyoto Protocol that
have agreed to a target for their greenhouse-gas emissions,
including all the Annex I countries (as amended in 1998) except
for Turkey and Belarus. See Kyoto Protocol
Annular modes
Preferred patterns of change in atmospheric circulation
corresponding to changes in the zonally averaged mid-latitude
westerlies. The Northern Annular Mode has a bias to the North
Atlantic and has a large correlation with the North Atlantic
Oscillation. The Southern Annular Mode occurs in the Southern
Hemisphere. The variability of the mid-latitude westerlies has
also been known as zonal flow (or wind) vacillation, and defined
through a zonal index. [WGI Box 3.4]
Anthropogenic
Resulting from or produced by human beings.
Aquaculture
The managed cultivation of aquatic plants or animals such
as salmon or shellfish held in captivity for the purpose of
harvesting.
Aquifer
A stratum of permeable rock that bears water. An unconfined
aquifer is recharged directly by local rainfall, rivers and lakes,
and the rate of recharge will be influenced by the permeability
of the overlying rocks and soils.
Arid region
A land region of low rainfall, where low is widely accepted to
be less than 250 mm precipitation per year.
Atlantic Multi-decadal Oscillation (AMO)
A multi-decadal (65 to 75 year) fluctuation in the North Atlantic,
in which sea surface temperatures showed warm phases during
roughly 1860 to 1880 and 1930 to 1960 and cool phases during
1905 to 1925 and 1970 to 1990 with a range of order 0.4o C.
Atmosphere
The gaseous envelope surrounding the Earth. The dry atmosphere
consists almost entirely of nitrogen (78.1% volume mixing
ratio) and oxygen (20.9% volume mixing ratio), together with
a number of trace gases, such as argon (0.93% volume mixing
ratio), helium and radiatively active greenhouse gases such as
carbon dioxide (0.035% volume mixing ratio) and ozone. In
168
addition, the atmosphere contains the greenhouse gas water
vapour, whose amounts are highly variable but typically around
1% volume mixing ratio. The atmosphere also contains clouds
and aerosols.
Atmospheric boundary layer
The atmospheric layer adjacent to the Earth’s surface that is
affected by friction against that boundary surface, and possibly
by transport of heat and other variables across that surface
(AMS, 2000). The lowest 10 metres or so of the boundary
layer, where mechanical generation of turbulence is dominant,
is called the surface boundary layer or surface layer.
Attribution
See Detection and attribution.
B.
Barrier
Any obstacle to reaching a goal, adaptation or mitigation
potential that can be overcome or attenuated by a policy,
programme, or measure. Barrier removal includes correcting
market failures directly or reducing the transactions costs in
the public and private sectors by e.g., improving institutional
capacity, reducing risk and uncertainty, facilitating market
transactions, and enforcing regulatory policies.
Baseline
Reference for measurable quantities from which an alternative
outcome can be measured, e.g., a non-intervention scenario
used as a reference in the analysis of intervention scenarios.
Basin
The drainage area of a stream, river, or lake.
Biodiversity
The total diversity of all organisms and ecosystems at various
spatial scales (from genes to entire biomes).
Bioenergy
Energy derived from biomass.
Biofuel
A fuel produced from organic matter or combustible oils
produced by plants. Examples of biofuel include alcohol,
black liquor from the paper-manufacturing process, wood, and
soybean oil.
Biomass
The total mass of living organisms in a given area or volume;
recently dead plant material is often included as dead biomass.
The quantity of biomass is expressed as a dry weight or as the
energy, carbon, or nitrogen content.
Biome
A major and distinct regional element of the biosphere,
typically consisting of several ecosystems (e.g., forests, rivers,
ponds, swamps within a region of similar climate). Biomes are
characterised by typical communities of plants and animals.
Appendix II: Glossary
Biosphere (terrestrial and marine)
The part of the Earth system comprising all ecosystems and
living organisms, in the atmosphere, on land (terrestrial
biosphere) or in the oceans (marine biosphere), including
derived dead organic matter, such as litter, soil organic matter
and oceanic detritus.
Biota
All living organisms of an area; the flora and fauna considered
as a unit.
Black carbon
Operationally defined aerosol species based on measurement of
light absorption and chemical reactivity and/or thermal stability;
consists of soot, charcoal and/or possible light absorbing
refractory organic matter.
Bog
Peat-accumulating acidic wetland.
Boreal forest
Forests of pine, spruce, fir, and larch stretching from the east
coast of Canada westward to Alaska and continuing from
Siberia westward across the entire extent of Russia to the
European Plain.
Boundary layer
See Atmospheric boundary layer.
C.
C3 plants
Plants that produce a three-carbon compound during
photosynthesis, including most trees and agricultural crops such
as rice, wheat, soybeans, potatoes and vegetables.
C4 plants
Plants, mainly of tropical origin, that produce a four-carbon
compound during photosynthesis, including many grasses and
the agriculturally important crops maize, sugar cane, millet and
sorghum.
Carbon (dioxide) capture and storage (CCS)
A process consisting of separation of carbon dioxide from
industrial and energy-related sources, transport to a storage
location, and long-term isolation from the atmosphere.
Carbon cycle
The term used to describe the flow of carbon (in various
forms, e.g., as carbon dioxide) through the atmosphere, ocean,
terrestrial biosphere and lithosphere.
Carbon dioxide (CO2)
A naturally occurring gas, also a by-product of burning fossil
fuels from fossil carbon deposits, such as oil, gas and coal, of
burning biomass and of land use changes and other industrial
processes. It is the principal anthropogenic greenhouse gas
that affects the Earth’s radiative balance. It is the reference
gas against which other greenhouse gases are measured and
therefore has a Global Warming Potential of 1.
Carbon dioxide (CO2) enrichment
See Carbon dioxide (CO2) fertilisation.
Carbon dioxide (CO2) fertilisation
The enhancement of the growth of plants as a result of increased
atmospheric carbon dioxide (CO2) concentration. Depending on
their mechanism of photosynthesis, certain types of plants are
more sensitive to changes in atmospheric CO2 concentration.
Carbon sequestration
The uptake of carbon containing substances, in particular
carbon dioxide. See Sequestration.
Catchment
An area that collects and drains rainwater.
Cholera
A water-borne intestinal infection caused by a bacterium (Vibrio
cholerae) that results in frequent watery stools, cramping
abdominal pain, and eventual collapse from dehydration and
shock.
Clean Development Mechanism (CDM)
Defined in Article 12 of the Kyoto Protocol, the CDM is intended
to meet two objectives: (1) to assist parties not included in Annex
I in achieving sustainable development and in contributing
to the ultimate objective of the Convention; and (2) to assist
parties included in Annex I in achieving compliance with their
quantified emission limitation and reduction commitments.
Certified Emission Reduction Units from CDM projects
undertaken in non-Annex I countries that limit or reduce
greenhouse gas emissions, when certified by operational entities
designated by Conference of the Parties/Meeting of the Parties,
can be accrued to the investor (government or industry) from
parties in Annex B. A share of the proceeds from the certified
project activities is used to cover administrative expenses as
well as to assist developing country parties that are particularly
vulnerable to the adverse effects of climate change to meet the
costs of adaptation.
Climate
Climate in a narrow sense is usually defined as the average
weather, or more rigorously, as the statistical description in
terms of the mean and variability of relevant quantities over a
period of time ranging from months to thousands or millions
of years. The classical period for averaging these variables is
30 years, as defined by the World Meteorological Organization.
The relevant quantities are most often surface variables such as
temperature, precipitation and wind. Climate in a wider sense
is the state, including a statistical description, of the climate
system.
Climate change
Climate change refers to a change in the state of the climate that
can be identified (e.g., by using statistical tests) by changes in the
mean and/or the variability of its properties, and that persists for
169
Appendix II: Glossary
an extended period, typically decades or longer. Climate change
may be due to natural internal processes or external forcings,
or to persistent anthropogenic changes in the composition of
the atmosphere or in land use. Note that the United Nations
Framework Convention on Climate Change (UNFCCC), in
its Article 1, defines climate change as: ‘a change of climate
which is attributed directly or indirectly to human activity that
alters the composition of the global atmosphere and which is in
addition to natural climate variability observed over comparable
time periods’. The UNFCCC thus makes a distinction between
climate change attributable to human activities altering the
atmospheric composition, and climate variability attributable
to natural causes. See also Climate variability; Detection and
attribution.
Climate feedback
An interaction mechanism between processes in the climate
system is called a climate feedback when the result of an
initial process triggers changes in a second process that in turn
influences the initial one. A positive feedback intensifies the
original process, and a negative feedback reduces it.
Climate model
A numerical representation of the climate system based on the
physical, chemical and biological properties of its components,
their interactions and feedback processes, and accounting for
all or some of its known properties. The climate system can be
represented by models of varying complexity, that is, for any
one component or combination of components a spectrum or
hierarchy of models can be identified, differing in such aspects as
the number of spatial dimensions, the extent to which physical,
chemical or biological processes are explicitly represented, or
the level at which empirical parameterisations are involved.
Coupled atmosphere-ocean general circulation models
(AOGCMs) provide a representation of the climate system that
is near the most comprehensive end of the spectrum currently
available. There is an evolution towards more complex models
with interactive chemistry and biology (see WGI Chapter 8).
Climate models are applied as a research tool to study and
simulate the climate, and for operational purposes, including
monthly, seasonal and interannual climate predictions.
Climate projection
A projection of the response of the climate system to emissions
or concentration scenarios of greenhouse gases and aerosols,
or radiative forcing scenarios, often based upon simulations
by climate models. Climate projections are distinguished from
climate predictions in order to emphasise that climate projections
depend upon the emission/concentration/radiative forcing
scenario used, which are based on assumptions concerning, for
example, future socioeconomic and technological developments
that may or may not be realised and are therefore subject to
substantial uncertainty.
Climate scenario
A plausible and often simplified representation of the future
climate, based on an internally consistent set of climatological
relationships that has been constructed for explicit use in
170
investigating the potential consequences of anthropogenic
climate change, often serving as input to impact models.
Climate projections often serve as the raw material for
constructing climate scenarios, but climate scenarios usually
require additional information such as about the observed
current climate. A climate change scenario is the difference
between a climate scenario and the current climate.
Climate system
The climate system is the highly complex system consisting
of five major components: the atmosphere, the hydrosphere,
the cryosphere, the land surface and the biosphere, and the
interactions between them. The climate system evolves in time
under the influence of its own internal dynamics and because
of external forcings such as volcanic eruptions, solar variations
and anthropogenic forcings such as the changing composition
of the atmosphere and land-use change.
Climate variability
Climate variability refers to variations in the mean state and
other statistics (such as standard deviations, the occurrence of
extremes, etc.) of the climate on all spatial and temporal scales
beyond that of individual weather events. Variability may be due
to natural internal processes within the climate system (internal
variability), or to variations in natural or anthropogenic external
forcing (external variability). See also Climate change.
CO2
See Carbon dioxide.
CO2-fertilisation
See Carbon dioxide fertilisation.
Confidence
The level of confidence in the correctness of a result is expressed
in this Technical Paper using a standard terminology defined in
Box 1.1. See also Likelihood; Uncertainty.
Control run
A model run carried out to provide a baseline for comparison
with climate-change experiments. The control run uses constant
values for the radiative forcing due to greenhouse gases,
appropriate to present-day or pre-industrial conditions.
Coral
The term coral has several meanings, but is usually the common
name for the Order Scleractinia, all members of which have hard
limestone skeletons, and which are divided into reef-building and
non-reef-building, or cold- and warm-water corals. See Coral reefs
Coral reefs
Rock-like limestone structures built by corals along ocean
coasts (fringing reefs) or on top of shallow, submerged banks or
shelves (barrier reefs, atolls), most conspicuous in tropical and
subtropical oceans.
Cost
The consumption of resources such as labour time, capital,
Appendix II: Glossary
materials, fuels, etc. as a consequence of an action. In economics
all resources are valued at their opportunity cost, being the value
of the most valuable alternative use of the resources. Costs are
defined in a variety of ways and under a variety of assumptions
that affect their value. Cost types include: administrative costs,
damage costs (to ecosystems, people and economies due to
negative effects from climate change), and implementation costs
of changing existing rules and regulation, capacity building
efforts, information, training and education, etc. Private costs
are carried by individuals, companies or other private entities
that undertake the action, whereas social costs include also the
external costs on the environment and on society as a whole.
The negative of costs are benefits (also sometimes called
negative costs). Costs minus benefits are net costs.
Cryosphere
The component of the climate system consisting of all snow, ice
and frozen ground (including permafrost) on and beneath the
surface of the Earth and ocean. See also Glacier; Ice sheet.
D.
Deforestation
Conversion of forest to non-forest. For a discussion of the term
forest and related terms such as afforestation, reforestation,
and deforestation see the IPCC Report on Land Use, Land-Use
Change and Forestry (IPCC, 2000).
Dengue fever
An infectious viral disease spread by mosquitoes, often called
breakbone fever because it is characterised by severe pain in the
joints and back. Subsequent infections of the virus may lead to
dengue haemorrhagic fever (DHF) and dengue shock syndrome
(DSS), which may be fatal.
Desert
A region of very low rainfall, where ‘very low’ is widely
accepted to be less than 100 mm per year.
Desertification
Land degradation in arid, semi-arid and dry sub-humid areas
resulting from various factors, including climatic variations and
human activities. Further, the United Nations Convention to
Combat Desertification (UNCCD) defines land degradation as
a reduction or loss in arid, semi-arid, and dry sub-humid areas
of the biological or economic productivity and complexity of
rain-fed cropland, irrigated cropland, or range, pasture, forest
and woodlands resulting from land uses or from a process or
combination of processes, including those arising from human
activities and habitation patterns, such as: (i) soil erosion
caused by wind and/or water; (ii) deterioration of the physical,
chemical, and biological or economic properties of soil; and
(iii) long-term loss of natural vegetation.
Detection and attribution
Climate varies continually on all time scales. Detection of
climate change is the process of demonstrating that climate has
changed in some defined statistical sense, without providing a
reason for that change. Attribution of causes of climate change
is the process of establishing the most likely causes for the
detected change with some defined level of confidence.
Development path or pathway
An evolution based on an array of technological, economic,
social, institutional, cultural, and biophysical characteristics that
determine the interactions between natural and human systems,
including production and consumption patterns in all countries,
over time at a particular scale. Alternative development paths
refer to different possible trajectories of development, the
continuation of current trends being just one of the many
paths.
Disturbance regime
Frequency, intensity, and types of disturbances, such as fires,
insect or pest outbreaks, floods and droughts.
Downscaling
Downscaling is a method that derives local-to-regional-scale
(10 to 100km) information from larger-scale models or data
analyses. Two main methods are distinguished: dynamical
downscaling and empirical/statistical downscaling. The
dynamical method uses the output of regional climate models,
global models with variable spatial resolution or high-resolution
global models. The empirical/statistical methods develop
statistical relationships that link the large-scale atmospheric
variables with local/regional climate variables. In all cases, the
quality of the downscaled product depends on the quality of the
driving model.
Drought
In general terms, drought is a ‘prolonged absence or marked
deficiency of precipitation’, a ‘deficiency that results in water
shortage for some activity or for some group’, or a ‘period of
abnormally dry weather sufficiently prolonged for the lack
of precipitation to cause a serious hydrological imbalance’
(Heim, 2002). Drought has been defined in a number of
ways. Agricultural drought relates to moisture deficits in
the topmost 1 metre or so of soil (the root zone) that affect
crops, meteorological drought is mainly a prolonged deficit of
precipitation, and hydrologic drought is related to below-normal
streamflow, lake and groundwater levels. A megadrought is a
longdrawn out and pervasive drought, lasting much longer than
normal, usually a decade or more.
Dyke
A human-made wall or embankment along a shore to prevent
flooding of low-lying land.
Dynamic global vegetation model (DGVM)
Models that simulate vegetation development and dynamics
through space and time, as driven by climate and other
environmental changes.
Dynamical ice discharge
Discharge of ice from ice sheets or ice caps caused by the dynamics
of the ice sheet or ice cap (e.g., in the form of glacier flow, ice
streams and calving icebergs) rather than by melt or runoff.
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Appendix II: Glossary
E.
Ecological community
A community of plants and animals characterised by a
typical assemblage of species and their abundances. See also
Ecosystem.
Ecosystem
A system of living organisms interacting with each other and their
physical environment. The boundaries of what could be called
an ecosystem are somewhat arbitrary, depending on the focus of
interest or study. Thus, the extent of an ecosystem may range
from very small spatial scales to, ultimately, the entire Earth.
El Niño-Southern Oscillation (ENSO)
The term El Niño was initially used to describe a warm-water
current that periodically flows along the coast of Ecuador and
Perú, disrupting the local fishery. It has since become identified
with a basinwide warming of the tropical Pacific east of the
dateline. This oceanic event is associated with a fluctuation of
a global-scale tropical and subtropical surface pressure pattern
called the Southern Oscillation. This coupled atmosphere-ocean
phenomenon, with preferred time scales of two to about seven
years, is collectively known as El Niño-Southern Oscillation,
or ENSO. It is often measured by the surface pressure anomaly
difference between Darwin and Tahiti and the sea surface
temperatures in the central and eastern equatorial Pacific.
During an ENSO event, the prevailing trade winds weaken,
reducing upwelling and altering ocean currents such that the
sea surface temperatures warm, further weakening the trade
winds. This event has a great impact on the wind, sea surface
temperature and precipitation patterns in the tropical Pacific. It
has climatic effects throughout the Pacific region and in many
other parts of the world, through global teleconnections. The
cold phase of ENSO is called La Niña.
Emissions scenario
A plausible representation of the future development of
emissions of substances that are potentially radiatively active
(e.g., greenhouse gases, aerosols), based on a coherent and
internally consistent set of assumptions about driving forces
(such as demographic and socioeconomic development,
technological change) and their key relationships. Concentration
scenarios, derived from emission scenarios, are used as input
to a climate model to compute climate projections. See SRES
scenarios.
Endemic
Restricted or peculiar to a locality or region. With regard to
human health, endemic can refer to a disease or agent present
or usually prevalent in a population or geographical area at all
times.
Energy
The amount of work or heat delivered. Energy is classified in
a variety of types and becomes useful to human ends when it
flows from one place to another or is converted from one type
into another. Primary energy (also referred to as energy sources)
is the energy embodied in natural resources (e.g., coal, crude oil,
172
natural gas, uranium) that has not undergone any anthropogenic
conversion. This primary energy needs to be converted and
transported to become usable energy (e.g., light). Renewable
energy is obtained from the continuing or repetitive currents of
energy occurring in the natural environment, and includes noncarbon technologies such as solar energy, hydropower, wind,
tide and waves, and geothermal heat, as well as carbon neutral
technologies such as biomass. Embodied energy is the energy
used to produce a material substance (such as processed metals,
or building materials), taking into account energy used at the
manufacturing facility (zero order), energy used in producing
the materials that are used in the manufacturing facility (first
order), and so on.
Ensemble
A group of parallel model simulations used for climate
projections. Variation of the results across the ensemble members
gives an estimate of uncertainty. Ensembles made with the
same model but different initial conditions only characterise the
uncertainty associated with internal climate variability, whereas
multi-model ensembles including simulations by several
models also include the impact of model differences. Perturbedparameter ensembles, in which model parameters are varied in
a systematic manner, aim to produce a more objective estimate
of modelling uncertainty than is possible with traditional multimodel ensembles.
Epidemic
Occurring suddenly in incidence rates clearly in excess of
normal expectancy, applied especially to infectious diseases
but may also refer to any disease, injury, or other health-related
event occurring in such outbreaks.
Equilibrium line
The boundary between the region on a glacier where there is a
net annual loss of ice mass (ablation area) and that where there
is a net annual gain (accumulation area). The altitude of this
boundary is referred to as equilibrium line altitude.
Erosion
The process of removal and transport of soil and rock by
weathering, mass wasting, and the action of streams, glaciers,
waves, winds, and underground water.
Eutrophication
The process by which a body of water (often shallow) becomes
(either naturally or by pollution) rich in dissolved nutrients,
with a seasonal deficiency in dissolved oxygen.
Evaporation
The transition process from liquid to gaseous state.
Evapotranspiration
The combined process of water evaporation from the Earth’s
surface and transpiration from vegetation.
External forcing
External forcing refers to a forcing agent outside the climate
Appendix II: Glossary
system causing a change in the climate system. Volcanic
eruptions, solar variations and anthropogenic changes in
the composition of the atmosphere and land-use change are
external forcings.
Fossil fuels
Carbon-based fuels from fossil hydrocarbon deposits, including
coal, peat, oil, and natural gas.
Extinction
The complete disappearance of an entire biological species.
Framework Convention on Climate Change
See United Nations Framework Convention on Climate Change
(UNFCCC).
Extirpation
The disappearance of a species from part of its range; local
extinction.
Freshwater lens
A lenticular fresh groundwater body that underlies an oceanic
island. It is underlain by saline water.
Extreme weather event
An event that is rare at a particular place and time of year.
Definitions of “rare” vary, but an extreme weather event would
normally be as rare as or rarer than the 10th or 90th percentile
of the observed probability density function. By definition,
the characteristics of what is called extreme weather may vary
from place to place in an absolute sense. Single extreme events
cannot be simply and directly attributed to anthropogenic
climate change, as there is always a finite chance the event
in question might have occurred naturally. When a pattern of
extreme weather persists for some time, such as a season, it may
be classed as an extreme climate event, especially if it yields an
average or total that is itself extreme (e.g., drought or heavy
rainfall over a season).
Frozen ground
Soil or rock in which part or all of the pore water is frozen.
Frozen ground includes permafrost. Ground that freezes and
thaws annually is called seasonally frozen ground.
F.
Feedback
See Climate feedback.
Food chain
The chain of trophic relationships formed if several species
feed on each other. See Food web.
Food security
A situation that exists when people have secure access to
sufficient amounts of safe and nutritious food for normal growth,
development and an active and healthy life. Food insecurity may
be caused by the unavailability of food, insufficient purchasing
power, inappropriate distribution, or inadequate use of food at
the household level.
Food web
The network of trophic relationships within an ecological
community involving several interconnected food chains.
Forcing
See External forcing.
Forest
A vegetation type dominated by trees. Many definitions of the term
forest are in use throughout the world, reflecting wide differences
in biogeophysical conditions, social structure, and economics.
Particular criteria apply under the Kyoto Protocol. For a discussion of
the term forest and related terms such as afforestation, reforestation,
and deforestation see the IPCC Special Report on Land Use, LandUse Change, and Forestry (IPCC, 2000).
G.
General circulation model
See Climate model.
Glacial lake
A lake formed by glacier meltwater, located either at the front
of a glacier (known as a proglacial lake), on the surface of a
glacier (supraglacial lake), within the glacier (englacial lake)
or at the glacier bed (subglacial lake).
Glacier
A mass of land ice which flows downhill under gravity (through
internal deformation and/or sliding at the base) and is constrained
by internal stress and friction at the base and sides. A glacier is
maintained by accumulation of snow at high altitudes, balanced
by melting at low altitudes or discharge into the sea. See Mass
balance.
Global warming
Global warming refers to the gradual increase, observed or
projected, in global average surface temperature, as one of the
consequences of radiative forcing caused by anthropogenic
emissions.
Globalisation
The growing integration and interdependence of countries
worldwide through the increasing volume and variety of crossborder transactions in goods and services, free international
capital flows, and the more rapid and widespread diffusion of
technology, information and culture.
Governance
The way government is understood has changed in response
to social, economic and technological changes over recent
decades. There is a corresponding shift from government
defined strictly by the nation-state to a more inclusive concept
of governance, recognising the contributions of various levels
of government (global, international, regional, local) and the
roles of the private sector, of non-governmental actors and of
civil society.
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Appendix II: Glossary
Greenhouse effect
Greenhouse gases effectively absorb thermal infrared radiation,
emitted by the Earth’s surface, by the atmosphere itself due to
the same gases, and by clouds. Atmospheric radiation is emitted
to all sides, including downward to the Earth’s surface. Thus
greenhouse gases trap heat within the surface-troposphere
system. This is called the greenhouse effect. Thermal infrared
radiation in the troposphere is strongly coupled to the temperature
of the atmosphere at the altitude at which it is emitted. In the
troposphere, the temperature generally decreases with height.
Effectively, infrared radiation emitted to space originates from
an altitude with a temperature of, on average, –19°C, in balance
with the net incoming solar radiation, whereas the Earth’s
surface is kept at a much higher temperature of, on average,
+14°C. An increase in the concentration of greenhouse gases
leads to an increased infrared opacity of the atmosphere, and
therefore to an effective radiation into space from a higher
altitude at a lower temperature. This causes a radiative forcing
that leads to an enhancement of the greenhouse effect, the socalled enhanced greenhouse effect.
Greenhouse gas (GHG)
Greenhouse gases are those gaseous constituents of the
atmosphere, both natural and anthropogenic, that absorb and
emit radiation at specific wavelengths within the spectrum of
thermal infrared radiation emitted by the Earth’s surface, the
atmosphere itself, and by clouds. This property causes the
greenhouse effect. Water vapour (H2O), carbon dioxide (CO2),
nitrous oxide (N2O), methane (CH4) and ozone (O3) are the
primary greenhouse gases in the Earth’s atmosphere. Moreover,
there are a number of entirely human-made greenhouse gases in
the atmosphere, such as the halocarbons and other chlorine and
bromine containing substances, dealt with under the Montreal
Protocol. Beside CO2, N2O and CH4, the Kyoto Protocol
deals with the greenhouse gases sulphur hexafluoride (SF6),
hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs).
Gross Domestic Product (GDP)
Gross Domestic Product (GDP) is the monetary value of all
goods and services produced within a nation.
Gross National Product (GNP)
Gross National Product (GNP) is the monetary value of all
goods and services produced by a nation’s economy, including
income generated abroad by domestic residents, but without
income generated by foreigners.
or group of closely associated organisms lives.
Hadley Circulation
A direct, thermally driven overturning cell in the atmosphere
consisting of poleward flow in the upper troposphere, subsiding
air into the subtropical anticyclones, return flow as part of the
trade winds near the surface, and with rising air near the equator
and the so-called Inter-Tropical Convergence Zone.
Herbaceous
Flowering, non-woody.
Heterotrophic respiration
The conversion of organic matter to carbon dioxide by organisms
other than plants.
Holocene
The Holocene is a geological epoch extending from about
11,600 years ago to the present.
Human system
Any system in which human organisations play a major role.
Often, but not always, the term is synonymous with society
or social system e.g., agricultural system, political system,
technological system, economic system.
Hydrological cycle
The cycle in which water evaporates from the oceans and the
land surface, is carried over the Earth in atmospheric circulation
as water vapour, condensates to form clouds, precipitates again
as rain or snow, is intercepted by trees and vegetation, provides
runoff on the land surface, infiltrates into soils, recharges
groundwater, discharges into streams and, ultimately, flows out
into the oceans, from which it will eventually evaporate again
(AMS, 2000). The various systems involved in the hydrological
cycle are usually referred to as hydrological systems.
Hydrological systems
See Hydrological cycle.
Hydrosphere
The component of the climate system comprising liquid surface
and subterranean water, such as oceans, seas, rivers, fresh water
lakes, underground water, etc.
Gross primary production
The total carbon fixed by plant through photosynthesis.
Hypolimnetic
Referring to the part of a lake below the thermocline made up
of water that is stagnant and of essentially uniform temperature
except during the period of overturn.
Groundwater recharge
The process by which external water is added to the zone of
saturation of an aquifer, either directly into a formation or
indirectly by way of another formation.
I.
Ice cap
A dome shaped ice mass, usually covering a highland area,
which is considerably smaller in extent than an ice sheet.
H.
Habitat
The locality or natural home in which a particular plant, animal,
Ice sheet
A mass of land ice that is sufficiently deep to cover most of
the underlying bedrock topography, so that its shape is mainly
174
Appendix II: Glossary
determined by its dynamics (the flow of the ice as it deforms
internally and/or slides at its base). An ice sheet flows outwards
from a high central ice plateau with a small average surface
slope. The margins usually slope more steeply, and most ice is
discharged through fast-flowing ice streams or outlet glaciers,
in some cases into the sea or into ice shelves floating on the
sea. There are only three large ice sheets in the modern world,
one on Greenland and two on Antarctica (the East and West
Antarctic ice sheets, divided by the Transantarctic Mountains).
During glacial periods there were others.
Ice shelf
A floating slab of ice of considerable thickness extending from
the coast (usually of great horizontal extent with a level or gently
sloping surface), often filling embayments in the coastline of
the ice sheets. Nearly all ice shelves are in Antarctica.
(Climate change) Impacts
The effects of climate change on natural and human systems.
Depending on the consideration of adaptation, one can
distinguish between potential impacts and residual impacts:
• Potential impacts: all impacts that may occur given
a projected change in climate, without considering
adaptation.
• Residual impacts: the impacts of climate change that would
occur after adaptation.
See also Market impacts and Non-market impacts.
Indigenous peoples
No internationally accepted definition of indigenous
peoples exists. Common characteristics often applied under
international law, and by United Nations agencies to distinguish
indigenous peoples include: residence within or attachment to
geographically distinct traditional habitats, ancestral territories,
and their natural resources; maintenance of cultural and social
identities, and social, economic, cultural and political institutions
separate from mainstream or dominant societies and cultures;
descent from population groups present in a given area, most
frequently before modern states or territories were created and
current borders defined; and self-identification as being part of
a distinct indigenous cultural group, and the desire to preserve
that cultural identity.
Indirect aerosol effect
Aerosols may lead to an indirect radiative forcing of the climate
system through acting as cloud condensation nuclei or modifying
the optical properties and lifetime of clouds. Two indirect effects
are distinguished:
Cloud albedo effect: A radiative forcing induced by an increase
in anthropogenic aerosols that cause an initial increase in droplet
concentration and a decrease in droplet size for fixed liquid
water content, leading to an increase in cloud albedo.
Cloud lifetime effect: A forcing induced by an increase in
anthropogenic aerosols that cause a decrease in droplet size,
reducing the precipitation efficiency, thereby modifying the
liquid water content, cloud thickness and cloud life time.
Apart from these indirect effects, aerosols may have a semidirect effect. This refers to the absorption of solar radiation by
absorbing aerosol, which heats the air and tends to increase
the static stability relative to the surface. It may also cause
evaporation of cloud droplets.
Infectious disease
Any disease caused by microbial agents that can be transmitted
from one person to another or from animals to people. This may
occur by direct physical contact, by handling of an object that
has picked up infective organisms, through a disease carrier, via
contaminated water, or by spread of infected droplets coughed
or exhaled into the air.
Infrastructure
The basic equipment, utilities, productive enterprises,
installations, and services essential for the development,
operation, and growth of an organisation, city, or nation.
Integrated water resources management (IWRM)
The prevailing concept for water management which, however,
has not been defined unambiguously. IWRM is based on four
principles that were formulated by the International Conference
on Water and the Environment in Dublin, 1992: 1) fresh water
is a finite and vulnerable resource, essential to sustain life,
development and the environment; 2) water development and
management should be based on a participatory approach,
involving users, planners and policymakers at all levels; 3)
women play a central part in the provision, management and
safeguarding of water; 4) water has an economic value in all its
competing uses and should be recognised as an economic good.
Interdecadal Pacific Oscillation (IPO)
Also known as the Pacific Decadal Oscillation (PDO). See North
Pacific Index. [For more detail see WGI Box 3.4]
Internal variability
See Climate variability.
Irrigation water-use efficiency
Irrigation water-use efficiency is the amount of biomass or seed
yield produced per unit irrigation water applied, typically about
1 tonne of dry matter per 100 mm water applied.
IS92 scenarios
See Emissions scenarios.
Isostacy
Isostacy refers to the way in which the lithosphere and mantle
respond visco-elastically to changes in surface loads. When
the loading of the lithosphere and/or the mantle is changed by
alterations in land ice mass, ocean mass, sedimentation, erosion
or mountain building, vertical isostatic adjustment results, in
order to balance the new load.
K.
Kyoto Protocol
The Kyoto Protocol to the United Nations Framework Convention
on Climate Change (UNFCCC) was adopted in 1997 in Kyoto,
Japan, at the Third Session of the Conference of the Parties (COP)
175
Appendix II: Glossary
to the UNFCCC. It contains legally binding commitments, in
addition to those included in the UNFCCC. Countries included
in Annex B of the Protocol (most Organization for Economic
Cooperation and Development countries and countries with
economies in transition) agreed to reduce their anthropogenic
greenhouse gas emissions (carbon dioxide, methane, nitrous
oxide, hydrofluorocarbons, perfluorocarbons, and sulphur
hexafluoride) by at least 5% below 1990 levels in the commitment
period 2008 to 2012. The Kyoto Protocol entered into force on 16
February 2005.
L.
La Niña
See El Niño-Southern Oscillation (ENSO).
Land use and Land-use change
Land use refers to the total of arrangements, activities and inputs
undertaken in a certain land cover type (a set of human actions).
The term land use is also used in the sense of the social and
economic purposes for which land is managed (e.g., grazing,
timber extraction, and conservation).
Land-use change refers to a change in the use or management of
land by humans, which may lead to a change in land cover. Land
cover and land-use change may have an impact on the surface
albedo, evapotranspiration, sources and sinks of greenhouse
gases, or other properties of the climate system and may thus
have a radiative forcing and/or other impacts on climate, locally
or globally. See also: the IPCC Report on Land Use, Land-Use
Change, and Forestry (IPCC, 2000).
Landfill
A landfill is a solid waste disposal site where waste is deposited
below, at or above ground level. Limited to engineered sites with
cover materials, controlled placement of waste and management
of liquids and gases. It excludes uncontrolled waste disposal.
Landslide
A mass of material that has slipped downhill by gravity, often
assisted by water when the material is saturated; the rapid
movement of a mass of soil, rock or debris down a slope.
Lapse rate
The rate of change of an atmospheric variable, usually temperature,
with height. The lapse rate is considered positive when the variable
decreases with height.
Latent heat flux
The flux of heat from the Earth’s surface to the atmosphere that
is associated with evaporation or condensation of water vapour at
the surface; a component of the surface energy budget.
Paper using a standard terminology defined in Box 1.1.
See also Confidence; Uncertainty.
Little Ice Age (LIA)
An interval between approximately AD 1400 and 1900 when
temperatures in the Northern Hemisphere were generally colder
than today’s, especially in Europe.
M.
Malaria
Endemic or epidemic parasitic disease caused by species of
the genus Plasmodium (Protozoa) and transmitted to humans
by mosquitoes of the genus Anopheles; produces bouts of high
fever and systemic disorders, affects about 300 million and kills
approximately 2 million people worldwide every year.
Market impacts
Impacts that can be quantified in monetary terms, and directly
affect gross domestic product – e.g., changes in the price of
agricultural inputs and/or goods. See Non-market impacts.
Mass balance (of glaciers, ice caps or ice sheets)
The balance between the mass input to an ice body (accumulation)
and the mass loss (ablation, iceberg calving). Mass balance terms
include the following:
Specific mass balance: net mass loss or gain over a hydrological
cycle at a point on the surface of a glacier.
Total mass balance (of the glacier): the specific mass balance
spatially integrated over the entire glacier area; the total mass a
glacier gains or loses over a hydrological cycle.
Mean specific mass balance: the total mass balance per unit
area of the glacier. If surface is specified (specific surface mass
balance, etc.) then ice-flow contributions are not considered;
otherwise, mass balance includes contributions from ice flow and
iceberg calving. The specific surface mass balance is positive in
the accumulation area and negative in the ablation area.
Meningitis
Inflammation of the meninges (part of the covering of the brain),
usually caused by bacteria, viruses or fungi.
Meridional overturning circulation (MOC)
A zonally averaged, large scale meridional (north-south)
overturning circulation in the oceans. In the Atlantic such a
circulation transports relatively warm upper-ocean waters
northward, and relatively cold deep waters southward. The Gulf
Stream forms part of this Atlantic circulation.
Leaching
The removal of soil elements or applied chemicals by water
movement through the soil.
Methane (CH4)
Methane is one of the six greenhouse gases to be mitigated
under the Kyoto Protocol and is the major component of
natural gas and associated with all hydrocarbon fuels, animal
husbandry and agriculture. Coal-bed methane is the gas found
in coal seams.
Likelihood
The likelihood of an occurrence, an outcome or a result, where this
can be estimated probabilistically, is expressed in this Technical
Millennium Development Goals (MDGs)
A set of time-bound and measurable goals for combating
poverty, hunger, disease, illiteracy, discrimination against
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Appendix II: Glossary
women and environmental degradation, agreed at the UN
Millennium Summit in 2000.
Mires
Peat-accumulating wetlands. See Bog.
Mitigation
Technological change and substitution that reduce resource
inputs and emissions per unit of output. Although several
social, economic and technological policies would produce an
emissions reduction, with respect to climate change, mitigation
means implementing policies to reduce greenhouse gas
emissions and enhance sinks.
Monsoon
A monsoon is a tropical and subtropical seasonal reversal in
both the surface winds and associated precipitation, caused by
differential heating between a continental-scale land mass and
the adjacent ocean. Monsoon rains occur mainly over land in
summer.
Montane
The biogeographic zone made up of relatively moist, cool
upland slopes below the sub-alpine zone that is characterised
by the presence of mixed deciduous at lower and coniferous
evergreen forests at higher elevations.
Morbidity
Rate of occurrence of disease or other health disorder within
a population, taking account of the age-specific morbidity
rates. Morbidity indicators include chronic disease incidence/
prevalence, rates of hospitalisation, primary care consultations,
disability-days (i.e., days of absence from work), and prevalence
of symptoms.
Mortality
Rate of occurrence of death within a population; calculation of
mortality takes account of age-specific death rates, and can thus
yield measures of life expectancy and the extent of premature
death.
N.
Net ecosystem production (NEP)
Net ecosystem production is the difference between net primary
production (NPP) and heterotrophic respiration (mostly
decomposition of dead organic matter) of that ecosystem over
the same area.
Net primary production (NPP)
Net primary production is the gross primary production minus
autotrophic respiration, i.e., the sum of metabolic processes for
plant growth and maintenance, over the same area.
Nitrous oxide (N2O)
One of the six types of greenhouse gases to be curbed under
the Kyoto Protocol. The main anthropogenic source of nitrous
oxide is agriculture (soil and animal manure management),
but important contributions also come from sewage treatment,
combustion of fossil fuel, and chemical industrial processes.
Nitrous oxide is also produced naturally from a wide variety
of biological sources in soil and water, particularly microbial
action in wet tropical forests.
No-regrets policy
A policy that would generate net social and/or economic
benefits irrespective of whether or not anthropogenic climate
change occurs.
Non-Governmental Organisation (NGO)
A non-profit group or association organised outside of
institutionalised political structures to realise particular
social and/or environmental objectives or serve particular
constituencies.
Non-linearity
A process is called non-linear when there is no simple
proportional relation between cause and effect. The climate
system contains many such non-linear processes, resulting in a
system with a potentially very complex behaviour.
Non-market impacts
Impacts that affect ecosystems or human welfare, but that are
not easily expressed in monetary terms, e.g., an increased risk
of premature death, or increases in the number of people at risk
of hunger. See also Market impacts.
North Atlantic Oscillation (NAO)
The North Atlantic Oscillation consists of opposing variations of
barometric pressure near Iceland and near the Azores. It therefore
corresponds to fluctuations in the strength of the main westerly
winds across the Atlantic into Europe, and thus to fluctuations in
the embedded cyclones with their associated frontal systems. See
WGI Box 3.4.
North Pacific Index (NPI)
The NPI is the average mean sea level pressure anomaly in
the Aleutian Low over the Gulf of Alaska (30oN- 65oN, 160oE140oW). It is an index of the Pacific Decadal Oscillation (also
known as the Interdecadal Pacific Oscillation). See WGI Box
3.4 for further information.
O.
Oil sands and oil shale
Unconsolidated porous sands, sandstone rock and shales
containing bituminous material that can be mined and converted
to a liquid fuel.
Ombrotrophic bog
An acidic peat-accumulating wetland that is rainwater (instead
of groundwater) fed and thus particularly poor in nutrients.
Ozone (O3)
Ozone, the tri-atomic form of oxygen, is a gaseous atmospheric
constituent. In the troposphere, ozone is created both naturally
and by photochemical reactions involving gases resulting
from human activities (smog). Troposphere ozone acts as a
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Appendix II: Glossary
greenhouse gas. In the stratosphere, ozone is created by the
interaction between solar ultraviolet radiation and molecular
oxygen (O2). Stratospheric ozone plays a dominant role in the
stratospheric radiative balance. Its concentration is highest in
the ozone layer.
P.
Pacific Decadal Oscillation (PDO)
Also known as the Interdecadal Pacific Oscillation (IPO). See
North Pacific Index. [WGI Box 3.4]
Pacific-North American (PNA) pattern
An atmospheric large-scale wave pattern featuring a sequence
of tropospheric high- and low-pressure anomalies stretching
from the subtropical west Pacific to the east coast of North
America. [WGI Box 3.4]
Peat
Peat is formed from dead plants, typically Sphagnum mosses,
which are only partially decomposed due to their permanent
submergence in water and the presence of conserving substances
such as humic acids.
Peatland
Typically a wetland such as a mire slowly accumulating peat.
Percentile
A percentile is a value on a scale of zero to one hundred that
indicates the percentage of the data set values that is equal to or
below it. The percentile is often used to estimate the extremes
of a distribution. For example, the 90th (10th) percentile may be
used to refer to the threshold for the upper (lower) extremes.
Permafrost
Ground (soil or rock and included ice and organic material) that
remains at or below 0°C for at least two consecutive years. See
also Frozen ground.
pH
pH is a dimensionless measure of the acidity of water (or any
solution). Pure water has a pH=7. Acid solutions have a pH
smaller than 7 and basic solutions have a pH larger than 7. pH
is measured on a logarithmic scale. Thus, a pH decrease of 1
unit corresponds to a 10-fold increase in the acidity.
Phenology
The study of natural phenomena in biological systems that
recur periodically (e.g., development stages, migration) and
their relation to climate and seasonal changes.
Photosynthesis
The process by which green plants, algae and some bacteria take
carbon dioxide from the air (or bicarbonate in water) to build
carbohydrates. There are several pathways of photosynthesis
with different responses to atmospheric carbon dioxide
concentrations. See Carbon dioxide fertilisation.
Plankton
Micro-organisms living in the upper layers of aquatic systems.
178
A distinction is made between phytoplankton, which depend on
photosynthesis for their energy supply, and zooplankton, which
feed on phytoplankton.
Policies
In United Nations Framework Convention on Climate Change
(UNFCCC) parlance, policies are taken and/or mandated by a
government—often in conjunction with business and industry
within its own country, or with other countries—to accelerate
mitigation and adaptation measures. Examples of policies
are carbon or other energy taxes, fuel efficiency standards for
automobiles, etc. Common and co-ordinated or harmonised
policies refer to those adopted jointly by parties.
Primary production
All forms of production accomplished by plants, also called
primary producers. See Gross primary production, Net primary
production and Net ecosystem production.
Projection
A potential future evolution of a quantity or set of quantities,
often computed with the aid of a model. Projections are
distinguished from predictions in order to emphasise that
projections involve assumptions concerning, for example,
future socioeconomic and technological developments that may
or may not be realised, and are therefore subject to substantial
uncertainty. See also Climate projection.
Proxy
A proxy climate indicator is a local record that is interpreted,
using physical and bio-physical principles, to represent some
combination of climate-related variations back in time. Climaterelated data derived in this way are referred to as proxy data.
Examples of proxies include pollen analysis, tree-ring records,
characteristics of corals and various data derived from ice
cores.
R.
Radiative forcing
Radiative forcing is the change in the net, downward minus
upward, irradiance (expressed in Watts per square metre, W/m2)
at the tropopause due to a change in an external driver of climate
change, such as, for example, a change in the concentration
of carbon dioxide or the output of the Sun. Radiative forcing
is computed with all tropospheric properties held fixed at
their unperturbed values, and after allowing for stratospheric
temperatures, if perturbed, to readjust to radiative-dynamical
equilibrium. Radiative forcing is called instantaneous if no
change in stratospheric temperature is accounted for. For the
purposes of this Technical Paper, radiative forcing is further
defined as the change relative to the year 1750 and, unless
otherwise noted, refers to a global and annual average value.
Rangeland
Unmanaged grasslands, shrublands, savannas and tundra.
Reconstruction
The use of climate indicators to help determine (generally past)
climates.
Appendix II: Glossary
Reforestation
Planting of forests on lands that have previously contained forests
but that have been converted to some other use. For a discussion
of the term forest and related terms such as afforestation,
reforestation and deforestation, see the IPCC Report on Land
Use, Land-Use Change and Forestry (IPCC, 2000).
Regime
A regime is a preferred state of the climate system, often
representing one phase of dominant patterns or modes of
climate variability.
Region
A region is a territory characterised by specific geographical
and climatological features. The climate of a region is affected
by regional and local scale forcings such as topography, landuse characteristics, lakes etc., as well as remote influences from
other regions.
Reservoir
An artificial or natural storage place for water, such as a lake,
pond or aquifer, from which the water may be withdrawn for
such purposes as irrigation or water supply.
Resilience
The ability of a social or ecological system to absorb disturbances
while retaining the same basic structure and ways of functioning,
the capacity for self-organisation, and the capacity to adapt to
stress and change.
Respiration
The process whereby living organisms convert organic matter
to carbon dioxide, releasing energy and consuming oxygen.
Riparian
Relating to or living or located on the bank of a natural
watercourse (such as a river) or sometimes of a lake or a
tidewater.
Runoff
That part of precipitation that does not evaporate and is not
transpired, but flows over the ground surface and returns to
bodies of water. See Hydrological cycle.
S.
Salinisation
The accumulation of salts in soils.
Saltwater intrusion
Displacement of fresh surface water or groundwater by the
advance of saltwater due to its greater density. This usually
occurs in coastal and estuarine areas due to reducing landbased influence (e.g., either from reduced runoff and associated
groundwater recharge, or from excessive water withdrawals
from aquifers) or increasing marine influence (e.g., relative
sea-level rise).
Savanna
Tropical or sub-tropical grassland or woodland biomes with
scattered shrubs, individual trees or a very open canopy of
trees, all characterised by a dry (arid, semi-arid or semi-humid)
climate.
Scenario
A plausible and often simplified description of how the future
may develop, based on a coherent and internally consistent
set of assumptions about driving forces and key relationships.
Scenarios may be derived from projections, but are often based
on additional information from other sources, sometimes
combined with a narrative storyline. See also SRES scenarios;
Climate scenario; Emissions scenarios.
Sea ice
Any form of ice found at sea that has originated from the
freezing of sea water. Sea ice may be discontinuous pieces (ice
floes) moved on the ocean surface by wind and currents (pack
ice), or a motionless sheet attached to the coast (land-fast ice).
Sea-ice biome
The biome formed by all marine organisms living within or on
the floating sea ice (frozen seawater) of the polar oceans.
Sea-level change/sea-level rise
Sea level can change, both globally and locally, due to (i)
changes in the shape of the ocean basins, (ii) changes in the total
mass of water and (iii) changes in water density. Factors leading
to sea-level rise under global warming include both increases
in the total mass of water from the melting of land-based snow
and ice, and changes in water density from an increase in ocean
water temperatures and salinity changes. Relative sea-level rise
occurs where there is a local increase in the level of the ocean
relative to the land, which might be due to ocean rise and/or
land-level subsidence.
Sea-level equivalent (SLE)
The change in global average sea level that would occur if a
given amount of water or ice were added to or removed from
the oceans.
Sea surface temperature (SST)
The sea surface temperature is the subsurface bulk temperature
in the top few metres of the ocean, measured by ships, buoys
and drifters. From ships, measurements of water samples in
buckets were mostly switched in the 1940s to samples from
engine intake water. Satellite measurements of skin temperature
(uppermost layer; a fraction of a millimetre thick) in the infrared
or the top centimetre or so in the microwave are also used, but
must be adjusted to be compatible with the bulk temperature.
Seasonally frozen ground
See Frozen ground.
Semi-arid regions
Regions of moderately low rainfall, which are not highly
productive and are usually classified as rangelands. ‘Moderately
low’ is widely accepted as between 100 and 250 mm precipitation
per year. See also Arid region.
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Appendix II: Glossary
Sensitivity
Sensitivity is the degree to which a system is affected, either
adversely or beneficially, by climate variability or climate
change. The effect may be direct (e.g., a change in crop yield
in response to a change in the mean, range, or variability of
temperature) or indirect (e.g., damages caused by an increase in
the frequency of coastal flooding due to sea-level rise).
Sequestration
Carbon storage in terrestrial or marine reservoirs. Biological
sequestration includes direct removal of CO2 from the
atmosphere through land-use change, afforestation,
reforestation, carbon storage in landfills and practices that
enhance soil carbon in agriculture.
•
•
•
Silviculture
Cultivation, development and care of forests.
Sink
Any process, activity or mechanism which removes a
greenhouse gas, an aerosol or a precursor of a greenhouse gas
or aerosol from the atmosphere.
Snow pack
A seasonal accumulation of slow-melting snow.
Snow water equivalent
The equivalent volume/mass of water that would be produced if
a particular body of snow or ice was melted.
Soil moisture
Water stored in or at the land surface and available for evaporation.
Source
Source mostly refers to any process, activity or mechanism
that releases a greenhouse gas, an aerosol, or a precursor of a
greenhouse gas or aerosol into the atmosphere. Source can also
refer to e.g., an energy source.
Southern Oscillation Index (SOI)
See El Niño-Southern Oscillation.
Spatial and temporal scales
Climate may vary on a large range of spatial and temporal scales.
Spatial scales may range from local (less than 100,000 km2),
through regional (100,000 to 10 million km2) to continental (10
to 100 million km2). Temporal scales may range from seasonal
to geological (up to hundreds of millions of years).
SRES scenarios
SRES scenarios are emissions scenarios developed by
Nakićenović and Swart (2000) and used, among others, as
a basis for some of the climate projections used in the IPCC
Fourth Assessment Report. The following terms are relevant
for a better understanding of the structure and use of the set of
SRES scenarios:
180
•
Scenario family: Scenarios that have a similar demographic,
societal, economic and technical-change storyline. Four
scenario families comprise the SRES scenario set: A1, A2,
B1 and B2.
Illustrative scenario: A scenario that is illustrative for
each of the six scenario groups reflected in the Summary
for Policymakers of Nakićenović and Swart (2000). They
include four revised ‘scenario markers’ for the scenario
groups A1B, A2, B1, B2, and two additional scenarios for
the A1FI and A1T groups. All scenario groups are equally
sound.
Marker scenario: A scenario that was originally posted
in draft form on the SRES website to represent a given
scenario family. The choice of markers was based on which
of the initial quantifications best reflected the storyline,
and the features of specific models. Markers are no more
likely than other scenarios, but are considered by the SRES
writing team as illustrative of a particular storyline. They
are included in revised form in Nakićenović and Swart
(2000). These scenarios received the closest scrutiny of
the entire writing team and via the SRES open process.
Scenarios were also selected to illustrate the other two
scenario groups.
Storyline: A narrative description of a scenario (or family of
scenarios), highlighting the main scenario characteristics,
relationships between key driving forces and the dynamics
of their evolution.
Stakeholder
A person or an organisation that has a legitimate interest in a
project or entity, or would be affected by a particular action or
policy.
Storm surge
The temporary increase, at a particular locality, in the height
of the sea due to extreme meteorological conditions (low
atmospheric pressure and/or strong winds). The storm surge is
defined as being the excess above the level expected from the
tidal variation alone at that time and place.
Storm tracks
Originally, a term referring to the tracks of individual cyclonic
weather systems, but now often generalised to refer to the
regions where the main tracks of extratropical disturbances
occur as sequences of low (cyclonic) and high (anticyclonic)
pressure systems.
Storyline
A narrative description of a scenario (or a family of scenarios)
that highlights the scenario’s main characteristics, relationships
between key driving forces, and the dynamics of the scenarios.
Stratosphere
The highly stratified region of the atmosphere above the
troposphere extending from about 10 km (ranging from 9 km
in high latitudes to 16 km in the tropics on average) to about 50
km altitude.
Appendix II: Glossary
Streamflow
Water flow within a river channel, for example expressed in
m3/s. A synonym for river discharge.
Subsidy
Direct payment from the government or a tax reduction to a
private party for implementing a practice the government wishes
to encourage. The reduction of greenhouse-gas emissions is
stimulated by lowering existing subsidies that have the effect
of raising emissions (such as subsidies to fossil fuel use) or by
providing subsidies for practices that reduce emissions or enhance
sinks (e.g., for insulation of buildings or for planting trees).
Succulent
Succulent plants, e.g., cactuses, possessing organs that store
water, thus facilitating survival during drought conditions.
Sustainable development
Development that meets the needs of the present without
compromising the ability of future generations to meet their
own needs.
T.
Taiga
The northernmost belt of boreal forest adjacent to the Arctic
tundra.
Technology
The practical application of knowledge to achieve particular
tasks that employs both technical artefacts (hardware,
equipment) and (social) information (“software”, know-how
for production and use of artefacts).
Teleconnection
A connection between climate variations over widely separated
parts of the world. In physical terms, teleconnections are often
a consequence of large-scale wave motions, whereby energy
is transferred from source regions along preferred paths in the
atmosphere.
Thermal expansion
In connection with sea-level rise, this refers to the increase in
volume (and decrease in density) that results from warming
water. A warming of the ocean leads to an expansion of the
ocean volume and hence an increase in sea level. See Sea-level
change.
Thermocline
The region in the world’s ocean, typically at a depth of 1 km,
where temperature decreases rapidly with depth and which
marks the boundary between the surface and the ocean.
Thermohaline circulation (THC)
Large-scale, density-driven circulation in the ocean, caused by
differences in temperature and salinity. In the North Atlantic,
the thermohaline circulation consists of warm surface water
flowing northward and cold deepwater flowing southward,
resulting in a net poleward transport of heat. The surface water
sinks in highly restricted regions located in high latitudes. Also
called Meridional Overturning Circulation (MOC).
Thermokarst
A ragged landscape full of shallow pits, hummocks and
depressions often filled with water (ponds), which results from
thawing of ground ice or permafrost. Thermokarst processes
are the processes driven by warming that lead to the formation
of thermokarst.
Threshold
The level of magnitude of a system process at which sudden or
rapid change occurs. A point or level at which new properties
emerge in an ecological, economic or other system, invalidating
predictions based on mathematical relationships that apply at
lower levels.
Transpiration
The evaporation of water vapour from the surfaces of leaves
through stomata. See Evapotranspiration.
Trend
In this Technical Paper, the word trend designates a change,
generally monotonic in time, in the value of a variable.
Trophic relationship
The ecological relationship which results when one species
feeds on another.
Troposphere
The lowest part of the atmosphere from the surface to about
10 km in altitude in mid-latitudes (ranging from 9 km in high
latitudes to 16 km in the tropics on average), where clouds and
weather phenomena occur. In the troposphere, temperatures
generally decrease with height.
Tundra
A treeless, level, or gently undulating plain characteristic of the
Arctic and sub-Arctic regions characterised by low temperatures
and short growing seasons.
U.
Uncertainty
An expression of the degree to which a value (e.g., the future
state of the climate system) is unknown. Uncertainty can
result from lack of information or from disagreement about
what is known or even knowable. It may have many types of
sources, from quantifiable errors in the data to ambiguously
defined concepts or terminology, or uncertain projections of
human behaviour. Uncertainty can therefore be represented
by quantitative measures, for example, a range of values
calculated by various models, or by qualitative statements, for
example, reflecting the judgement of a team of experts. See also
Likelihood; Confidence.
United Nations Framework Convention on Climate
Change (UNFCCC)
The Convention was adopted on 9 May 1992 in New York and
181
Appendix II: Glossary
signed at the 1992 Earth Summit in Rio de Janeiro by more
than 150 countries and the European Community. Its ultimate
objective is the ‘stabilisation of greenhouse gas concentrations
in the atmosphere at a level that would prevent dangerous
anthropogenic interference with the climate system’. It contains
commitments for all Parties. Under the Convention, Parties
included in Annex I (all OECD member countries in the year
1990 and countries with economies in transition) aim to return
greenhouse gas emissions not controlled by the Montreal
Protocol to 1990 levels by the year 2000. The Convention
entered in force in March 1994. See Kyoto Protocol.
Urbanisation
The conversion of land from a natural state or managed natural
state (such as agriculture) to cities; a process driven by net ruralto-urban migration through which an increasing percentage of
the population in any nation or region come to live in settlements
that are defined as urban centres.
V.
Vector
An organism, such as an insect, that transmits a pathogen from
one host to another.
Vector-borne diseases
Diseases that are transmitted between hosts by a vector organism
(such as a mosquito or tick); e.g., malaria, dengue fever and
leishmaniasis.
Vulnerability
Vulnerability is the degree to which a system is susceptible to,
and unable to cope with, adverse effects of climate change,
including climate variability and extremes. Vulnerability is a
function of the character, magnitude, and rate of climate change
and variation to which a system is exposed, its sensitivity, and
its adaptive capacity.
W.
Water consumption
Amount of extracted water irretrievably lost during its use (by
evaporation and goods production). Water consumption is equal
to water withdrawal minus return flow.
Water security
Reliable availability of water in sufficient quantity and quality
182
to sustain human health, livelihoods, production and the
environment.
Water stress
A country is water stressed if the available freshwater supply
relative to water withdrawals acts as an important constraint on
development. In global-scale assessments, basins with water
stress are often defined as having a per capita water availability
below 1,000 m3/yr (based on long-term average runoff).
Withdrawals exceeding 20% of renewable water supply have also
been used as an indicator of water stress. A crop is water stressed
if soil available water, and thus actual evapotranspiration, is less
than potential evapotranspiration demands.
Water-use efficiency
Carbon gain in photosynthesis per unit water lost in
evapotranspiration. It can be expressed on a short-term basis as
the ratio of photosynthetic carbon gain per unit transpirational
water loss, or on a seasonal basis as the ratio of net primary
production or agricultural yield to the amount of available
water.
Wetland
A transitional, regularly waterlogged area of poorly drained
soils, often between an aquatic and a terrestrial ecosystem,
fed from rain, surface water or groundwater. Wetlands are
characterised by a prevalence of vegetation adapted for life in
saturated soil conditions.
References
AMS, 2000: AMS Glossary of Meteorology, 2nd Edition. American
Meteorological Society, Boston, MA. http://amsglossary.
allenpress.com/glossary/browse.
Heim, R.R., 2002: A review of twentieth century drought indices
used in the United States. Bull. Am. Meteorol. Soc., 83, 11491165.
IPCC (Intergovernmental Panel on Climate Change), 2000: Land
Use, Land-Use Change and Forestry, R. T. Watson, I. R. Noble,
B. Bolin, N. H. Ravindranath, D. J. Verardo and D. J. Dokken,
Eds., Cambridge University Press, Cambridge, 375 pp.
IUCN, 1980: The World Conservation Strategy: living resource
conservation for sustainable development. IUCN/UNEP/WWF,
Gland.
Nakićenović, N. and R. Swart, Eds., 2000: Special Report on
Emissions Scenarios. Cambridge University Press, 599 pp.
Appendix III: Acronyms, chemical symbols,
scientific units
III.1
Acronyms and chemical symbols
ACIA
AIDS
AMO
AOGCM
AR4
ARD
CCS
CDM
CH4
CO2
CRU
DJF
ECLAC
ENSO
EROS
ES
EU
FAO
FAQ
FAR
GCM
GDP
GHCN
GHG
GLOF
GNP
GPCC
GPCP
HABs
HIV
IIASA
IPCC
IPO
IUCN
JJA
LIA
LULUCF
MARA/ARMA
MDG
MOC
N2O
NAM
Arctic Climate Impact Assessment
Acquired immune deficiency syndrome
Atlantic Multi-decadal Oscillation
Atmosphere–ocean general circulation model
Fourth Assessment Report (of the IPCC)
Afforestation, reforestation and
deforestation
Carbon capture and storage
Clean Development Mechanism
Methane, see Glossary
Carbon dioxide, see Glossary
Climatic Research Unit
December, January, February
Economic Commission for Latin
America and the Caribbean
El Niño–Southern Oscillation
Earth Resources Observation and Science
Executive Summary
European Union
Food and Agriculture Organization
Frequently Asked Questions
First Assessment Report (of the IPCC)
General circulation model
Gross domestic product
Global Historical Climatology Network
Greenhouse gas(es)
Glacial lake outburst flood
Gross national product
Global Precipitation Climatology Centre
Global Precipitation Climatology Project
Harmful algal blooms
Human immunodeficiency virus
International Institute for Applied
Systems Analysis
Intergovernmental Panel on Climate Change
Inter-decadal Pacific Oscillation
International Union for the Conservation
of Nature and Natural Resources (World
Conservation Union)
June, July, August
Little Ice Age
Land use, land-use change and forestry
Mapping Malaria Risk in Africa/Atlas du
Risque de la Malaria en Afrique
Millennium Development Goal
Meridional overturning circulation
Nitrous oxide, see Glossary
Northern Annular Mode
NAO
NASA
NGO
NH
OECD
PCBs
PDO
PDR
PDSI
pH
PNA
ppm
PREC/L
PSA
SAM
SAR
SD
SI
SIDS
SLE
SM
SOI
SPCZ
SPM
SRES
SST
SWE
SYR
TAR
TS
UK
UN
UNDP
UNFCCC
UNICEF
US$
USA
WCP
WGI
WGII
WGIII
WHO
WSP
North Atlantic Oscillation
National Aeronautics and Space
Administration
Non-governmental organisation
Northern Hemisphere
Organisation for Economic Co-operation
and Development
Polychlorinated biphenyls
Pacific Decadal Oscillation
People’s Democratic Republic
Palmer Drought Severity Index
See Glossary under pH
Pacific–North American (pattern)
Parts per million, see Appendix III.2
Precipitation Reconstruction over Land
Pacific–South American (pattern)
Southern Annular Mode
Second Assessment Report (of the IPCC)
Standard deviation
Suitability index
Small Island Developing States
Sea-level equivalent
Supplementary Material
Southern Oscillation Index
South Pacific Convergence Zone
Summary for Policymakers
Special Report on Emissions Scenarios
Sea surface temperature
Snow water equivalent
Synthesis Report (of the IPCC Fourth
Assessment)
Third Assessment Report (of the IPCC)
Technical Summary
United Kingdom
United Nations
United Nations Development Programme
United Nations Framework Convention
on Climate Change
United Nations Children’s Fund
United States dollar
United States of America
World Climate Programme
Working Group I (of the IPCC)
Working Group II (of the IPCC)
Working Group III (of the IPCC)
World Health Organization
Water safety plan
183
Appendix III: Acronyms, chemical symbols, scientific units
III.2
Scientific units
SI (Système Internationale) units
Physical quantity
Name of unit length mass
time
thermodynamic temperature
energy metre
kilogram
second
kelvin
joule
Fraction Symbol Multiple Prefix
Fractions and multiples
Prefix
10
deci
d
10-2 centi
c
10-3 milli
m
10-6 micro µ
10-9 nano
n
10-12 pico
p
10-15 femto f
10-18 atto
a
-1 ppm
watt
yr
184
m
kg
s
K
J
10
deca
102 hecto
103 kilo
106 mega
109 giga
1012 tera
1015 peta
1018 exa
Non-SI units, quantities and related abbreviations
°C
Symbol
Symbol
da
h
k
M
G
T
P
E
degree Celsius (0°C = 273 K approximately); temperature differences are also given in °C (=K) rather than the more correct
form of “Celsius degrees”
mixing ratio (as concentration measure of GHGs): parts per million (106) by volume
power or radiant flux; 1 watt = 1 joule / second = 1 kg m2 / s3
year
Appendix IV: List of Authors
Bates, Bryson
CSIRO
Australia
Kitoh, Akio
Japan Meteorological Agency
Japan
Kundzewicz, Zbigniew W.
Polish Academy of Sciences, Poland, and
Potsdam Institute for Climate Impact Research, Germany
Kovats, Sari
London School of Hygiene and Tropical Medicine
UK
Wu, Shaohong
Institute of Geographical Sciences and Natural Resources
Research
Chinese Academy of Sciences
China
Kumar, Pushpam
University of Liverpool
UK
Arnell, Nigel
Walker Institute for Climate System Research at the University
of Reading
UK
Burkett, Virginia
US Geological Survey
USA
Döll, Petra
University of Frankfurt
Germany
Gwary, Daniel
University of Maiduguri
Nigeria
Hanson, Clair
Met Office Hadley Centre
UK
Heij, BertJan
Bergonda Science Communication
The Netherlands
Magadza, Christopher H.D.
University of Zimbabwe
Zimbabwe
Martino, Daniel
Carbosur
Uruguay
Mata, Luis José
Nord-Süd Zentrum für Entwicklungsforschung
Germany/Venezuela
Medany, Mahmoud
The Central Laboratory for Agricultural Climate
Egypt
Miller, Kathleen
National Center for Atmospheric Research
USA
Oki, Taikan
University of Tokyo
Japan
Osman, Balgis
Higher Council for Environment and Natural Resources
Sudan
Jiménez, Blanca Elena
Universidad Nacional Autónoma de México
Mexico
Palutikof, Jean
Met Office Hadley Centre
UK
Kaser, Georg
University of Innsbruck
Austria
Prowse, Terry
Environment Canada and University of Victoria
Canada
185
Appendix IV: List of Authors
Pulwarty, Roger
NOAA/CIRES/Climate Diagnostics Center
USA/Trinidad and Tobago
Dai, Aiguo
National Center for Atmospheric Research
USA
Räisänen, Jouni
University of Helsinki
Finland
Milly, Christopher
US Geological Survey
USA
Renwick, James
National Institute of Water and Atmospheric Research
New Zealand
Mortsch, Linda
Environment Canada
Canada
Tubiello, Francesco Nicola
Columbia University
USA/IIASA/Italy
Nurse, Leonard
University of the West Indies, Cave Hill Campus
Barbados
Wood, Richard
Met Office Hadley Centre
UK
Payne, Richard
Department of Agriculture and Food Western Australia
Australia
Zhao, Zong-Ci
China Meteorological Administration
China
Arblaster, Julie
National Center for Atmospheric Research, USA and Bureau
of Meteorology, Australia
Pinskwar, Iwona
Polish Academy of Sciences
Poland
Betts, Richard
Met Office Hadley Centre
UK
186
Wilbanks, Tom
Oak Ridge National Laboratory
USA
Appendix V: List of Reviewers
Andressen, Rigoberto
Universidad de Los Andes
Venezuela
Asanuma, Jun
University of Tsukuba
Japan
Bandyopadhyay, Jayanta
Indian Institute of Management
India
Bayoumi, Attia
Ministry of Water Resources and Irrigation
Egypt
Bergström, Sten
Swedish Meteorological and Hydrological Institute
Sweden
Bernstein, Leonard
International Petroleum Industry Environmental
Conservation Association
UK
Bidegain, Mario
Uruguay
Bojariu, Roxana
National Meteorological Administration
Romania
de Loë, Rob
University of Guelph
Canada
Diaz Morejon, Cristobel Felix
Ministry of Science, Technology and the
Environment
Cuba
Elgizouli, Ismail
Higher Council for Environment and Natural
Resources
Sudan
Fobil, Julius
University of Ghana, Legon
Ghana
Folland, Chris
Met Office Hadley Centre
UK
Gallart, Francesc
CSIC
Spain
Gerten, Dieter
Potsdam Institute for Climate Impact Research
Germany
Gillett, Nathan
University of East Anglia
UK
Ginzo, Héctor
Ministerio de Relaciones Exteriores
Argentina
Grabs, Wolfgang
World Meteorological Organization
Switzerland
Hatfield, Jerry
US Department of Agriculture
USA
Jacob, Daniela
Max Planck Institute for Meteorology
Germany
187
Appendix V: List of Reviewers
Jacobs, Katharine
Arizona Universities
USA
Liu, Chunzhen
Ministry of Water Resources
China
Jeffrey, Paul
Cranfield University
UK
Mares, Constantin
Romanian Academy of Technical Sciences
Romania
Jouzel, Jean
Institut Pierre-Simon Laplace
France
Mares, Ileana
Romanian Academy of Technical Sciences
Romania
Jin, Byung-bok
Environmental Management Corporation
Republic of Korea
Mariotti, Annarita
ENEA
Italy
Kadaja, Jüri
Estonian Research Institute of Agriculture
Estonia
Morgenschweis, Gerd
Water Resources Management
Germany
Kaser, Georg
University of Innsbruck
Austria
Müller, Lars
Climate Strategy
European Union (Germany)
Kimball, Bruce
US Department of Agriculture
USA
Njie, Momodou
Blue Gold Solutions
The Gambia
Knutson, Thomas
Princeton University
USA
Noda, Akira
Frontier Research Centre for Global Change
Japan
Komen, Gerbrand
Royal Netherlands Meteorological Institute
The Netherlands
Parry, Martin
Co-chair IPCC Working Group II
UK
Kotwicki, Vincent
Kuwait Institute for Scientific Research
Kuwait
Ragab, Ragab
Centre for Ecology and Hydrology
UK
Lal, Murari
CESDAC
India
Ren, Guoyu
National Climate Centre
China
Lapin, Milan
Comenius University
Slovakia
Robock, Alan
Rutgers University
USA
Leon, Alejandro
Universidad de Chile
Chile
Roy, Rene
Ouranos, Consortium on Climate Change
Canada
188
Appendix V: List of Reviewers
Savard, Martine M.
Natural Resources Canada
Canada
Trenberth, Kevin
National Center for Atmospheric Research
USA
Schipper, Lisa
Chulalongkorn University
Thailand
van Walsum, Paul
Wageningen University and Research Centre
The Netherlands
Şen, Zekai
Istanbul Technical University
Turkey
Wojciech, Majewski
Institute of Meteorology and Water Management
Poland
Sherwood, Steve
Yale University
USA
Wratt, David
National Institute of Water and Atmospheric
Research
New Zealand
Shim, Kyo-moon
National Institute of Agricultural Science and
Technology
South Korea
Wurzler, Sabine
North Rhine Westphalia State Agency for Nature,
Environment and Consumer Protection
Germany
Sorooshian, Soroosh
University of California, Irvine
USA
Yabi, Ibouraïma
LECREDE/DGAT/FLASH/UAC
Republic of Benin
Szolgay, Jan
Slovak University of Technology
Slovakia
Zhao, Zong-Ci
China Meteorological Administration
China
Tabet-Aoul, Mahi
Research Centre on Social and Cultural
Anthropology (CRASC)
Algeria
189
Appendix VI: Permissions to publish
Permissions to publish have been granted by the following copyright holders:
Figure 3.2: Reprinted with kind permission from Petra Döll.
Figure 3.3: Reprinted from Lehner, B. and Co-authors, 2005: Estimating the impact of global change on flood
and drought risks in Europe: a continental, integrated assessment. Climatic Change, 75, 273-299, with kind
permission from Springer Science and Business Media.
Figure 4.1(a): From Fischer, G. and Co-authors, 2002: Global agro-ecological assessment for agriculture
in the 21st century: methodology and results. Research Report RR-02-02. International Institute for Applied
Systems Analysis (IIASA), Laxenburg, Austria. Reprinted with kind permission of IIASA.
Figure 5.1: Reprinted by permission from Macmillan Publishers Ltd [Nature]: O’Reilly, C.M. and Coauthors, 2003: Climate change decreases aquatic ecosystem productivity of Lake Tanganyika, Africa. Nature,
424, 766-768. Copyright 2003.
Figure 5.3: From Hemp, A., 2005: Climate change-driven forest fires marginalize the impact of ice cap
wasting on Kilimanjaro. Glob. Change Biol., 11, 1013-1023. Reprinted with permission from Blackwell
Publishing Ltd.
Figure 5.4: From Arnell, N.W., 2006b: Climate change and water resources: a global perspective. Avoiding
Dangerous Climate Change, H.J. Schellnhuber, W. Cramer, N. Nakićenović, T. Wigley and G. Yohe, Eds.,
Cambridge University Press, Cambridge, 167-175. Reprinted with permission from Cambridge University
Press.
Figure 5.8(a): From Haylock, M.R. and Co-authors, 2006: Trends in total and extreme South American rainfall
1960-2000 and links with sea surface temperature. J. Climate, 19, 1490-1512. Reprinted with permission
from American Meteorological Society.
Figure 5.8(b): From Aguilar, E. and Co-authors, 2005: Changes in precipitation and temperature extremes
in Central America and northern South America, 1961–2003. J. Geophys. Res., 110, D23107, doi:10.1029/
2005JD006119. Copyright (2005) American Geophysical Union. Reproduced by permission of American
Geophysical Union.
Figure 5.12: From Smith, L.C. and Co-authors, 2005: Disappearing Arctic lakes. Science, 308, 1429. Reprinted
with permission from AAAS.
191
Index
Note: Page numbers in bold indicate page spans for entire chapters. Page numbers in italics denote tables,
figures and boxed material.
A
Adaptation, 4, 48-51
autonomous, 48, 63
examples, 50
limits on, 49
mitigation, potential conflicts with, 124
planned, 48-49, 63
supply-side and demand-side options, 48, 49
sustainable development implications, 130
vulnerability reduction by, 49
See also Mitigation
Adaptation, vulnerability and sustainable
development, 125-131
Africa, 50, 85
agriculture, 63-67
Asia, 88-90
Australia and New Zealand, 50, 92-93, 92
economy, insurance, tourism, industry and
transportation, 75
Europe, 50, 95-96
human health, 69
Latin America, 50, 100-102, 101
North America, 50, 104-106
polar regions, 50, 109
settlements and infrastructure, 74
small islands, 50, 110, 111-113
water supply and sanitation, 71-73
Aerosol processes, 15
Afforestation, 4, 59, 118, 120-121
Africa, 79-85, 128-129
adaptation and vulnerability, 50, 85
current observations, 79-81, 79-80
forest ecosystems, 60
Kilimanjaro, Mt., 82
lakes and rivers, 36, 129
pastoralist coping strategies, 64
precipitation, 16, 25, 59
projected changes, 81-85, 128-129
runoff, 21-22, 35
vulnerabilities, 66, 128
Agriculture, 59-67, 128
adaptation, vulnerability and sustainable
development, 63-67
biotechnology and, 65, 65
cropland drainage, 123, 123
cropland management (reduced tillage), 118,
120, 122-123
cropland management (water), 118, 120
crops, 61-62
fertiliser use, 10, 120
intensification of, 120
irrigation water requirements, 4, 10, 61, 62, 128
mitigation measures and water, 118, 120
modelling, 59
observations, 60, 61
projections, 60-63, 128
residue return, 122-123, 123
water management and GHG emissions, 123
water quality, effects on, 10
See also Agriculture: regional aspects; Irrigation
Agriculture: regional aspects
Africa, 81, 83, 84
Asia, 87, 88
Australia and New Zealand, 91
Europe, 95
Latin America, 97, 100
North America, 103-104
small islands, 111
Agro-forestry, 119
Algal blooms, 56, 68, 71
Alpine ecosystems, 58
Amphibians, 55, 58, 98
Annular Modes, 22-23, 31
Aquaculture, 66
193
Index
Arid and semi-arid areas
observed changes, 38
projected changes, 62, 127, 128
vulnerability, 3, 127
See also Droughts
Asia, 85-90, 129
adaptation and vulnerability, 50, 88-89
floods, 37, 86
glaciers, 86, 86, 129
lakes and rivers, 36
observed impacts, 85-87
precipitation, 16, 25
projected impacts and vulnerabilities, 87-88, 129
runoff, 20, 29, 45-46
water supply, 43, 129
Attribution for climate change, 15, 16-17
Australia and New Zealand, 90-94, 129
adaptation and vulnerability, 50, 92-93, 92
droughts, 38, 66
groundwater, 36
infrastructure, 129
observed changes, 90-91, 90
precipitation, 16, 59
projected changes, 91-92, 129
B
Bio-energy crops, 4, 117-119, 118
Biodiversity, 55, 128
Africa, 81, 84-85, 84
Asia, 87
Australia and New Zealand, 91-92
Europe, 95
Latin America, 97-98, 100
North America, 104
polar regions, 108
small islands, 111
Biofuels, 66
Biogeochemical feedbacks, 24
Biomass electricity, 118, 119
Biotechnology, 65, 65
Buildings, 74, 118, 119
C
Campylobacteriosis, 68
Carbon cycle, feedbacks, 24
Carbon dioxide and water dynamics, 60
See also Greenhouse gas (GHG) emissions
Carbon dioxide capture and storage (CCS), 117194
123, 118
Carbon dioxide fertilisation, 58
Carbon sinks, 24
Caribbean, 25, 110
See also Small islands
Chacaltaya Glacier, 35, 99
Climate
complexity of response, 15
feedbacks with hydrological cycle, 15, 23-24
models (see Climate models)
observed changes, 15-23
projected changes, 24-31
variability, large-scale patterns of, 22-23, 31
Climate change, 13-31
aggravation of other stresses by, 4, 130
attribution for, 15, 16-17
impacts on sustainable development, 47, 125-131
impacts on water resources, 35-47, 47, 125-131
mitigation measures (see Mitigation)
See also Linking of climate change and water
resources
Climate change and water, 5-11
background, scope and context, 7-11
climate-related drivers of freshwater systems,
24-31, 38-43
linking climate change to water resources, 33-51
negative impacts vs. benefits, global, 3, 127
observed changes, 8-9, 35-38
projected changes, 38-48
projected impacts by regions, 77-113, 128-130
projected impacts by sectors, 59-74, 127-128
projected impacts by systems, 55-58
summary, 1-4
Climate models, 3, 24-31, 48, 179
multi-model probabilistic approaches, 26-27, 48
observational needs, 135
projections from, 24-31, 135-136
scenarios/storylines, 9-10, 10, 24
Coastal areas
future impacts, 43, 57-58, 128
human settlements and infrastructure, 73, 74
Colorado River Basin, 51, 51, 105
Columbia River Basin, 106
Confidence levels. See Uncertainty
Costs and socio-economic aspects, 45-47, 74-75
Cryosphere
observed changes, 3, 19-20, 19-20, 35
projected changes, 27-28
Index
Cryptosporidiosis, 68, 71
Cyclones, tropical
observed changes, 17-18
projected changes, 27, 31, 41, 103
D
Dams
construction and decommissioning, 9-10, 136
greenhouse gas emissions from, 4, 122, 123, 130
water storage by, 10
Deforestation, 23, 59, 61
avoided/reduced, 118, 121
Deltas, projected impacts, 57, 99, 128
Desalinisation, 10, 46, 72, 130
greenhouse gas emissions from, 123, 124
Drinking water quality, 45, 67-68, 72
Droughts
frequency of 100-year droughts, projected, 42
human health and, 68
observed changes, 37, 38, 39
projected changes, 26-27, 41-42, 42-43, 127
See also specific regions
Dry areas. See Arid and semi-arid areas
Dust storms, 68
E
Economic growth, water use and, 9
Economy, 74-75
Ecosystems, 55-58, 127-128
Egypt, agriculture in, 83, 84
El Niño-Southern Oscillation (ENSO), 22, 31, 85
Energy
Africa, 80, 82
Asia, 88
Australia and New Zealand, 91
Europe, 95
infrastructure, 74
Latin America, 96, 98
mitigation measures and water, 118
North America, 103
small islands, 111
water management and GHG emissions, 123
ENSO. See El Niño-Southern Oscillation
Erosion, soil, 43, 57
Europe, 93-96, 129
adaptation and vulnerability, 50, 95-96
droughts, 38, 94-95, 94
flooding, damage estimates, 46
heatwave of 2003, 38
mountain ecosystems, 58
observed changes, 93, 93
precipitation, 25, 42, 59
projected changes, 29, 42, 93-95, 129
runoff, 21-22, 29, 35, 45, 129
water-stressed areas, 129
Evapotranspiration
feedbacks, 23
observed changes, 20-21
projected changes, 25-26, 27, 29
Extinctions, 55, 56-57, 84, 91, 98, 128
See also Biodiversity
F
Feedbacks of climate and hydrological cycle, 23-24
emissions and sinks, 24
land surface effects, 23
ocean circulation, 24
Fisheries, 62-63, 66, 130
adaptation strategies, 64
Mekong river example, 63
Floods
costs of future impacts, 46, 75
in Europe, 94-95, 94
frequency of 100-year floods, projected, 41
human health and, 68
impacts on transportation and infrastructure, 73-74
insurance and, 75
observed changes, 37-38, 37
projected changes, 26, 41-42, 41, 127
Food availability/security, 3, 59, 60-63, 65-66
Forests/forestry, 59-60, 60, 128
adaptation strategies, 64-65
agro-forestry, 119
biotechnology and, 65, 65
conversion to cropland, 117
ecosystems, 58
mitigation measures and water, 118
Frozen ground
observed changes, 19, 19, 35, 107
projected changes, 27-28, 43, 108, 130
Future research needs, 4, 133-137
G
Gangotri Glacier, 86, 86
Gaps in knowledge, 4, 133-137
Geothermal energy, 118, 119
greenhouse gas emissions from, 123, 124
195
Index
Glacial lake outburst floods (GLOFs), 20, 35, 68
prevention projects, 88, 89
Glaciers
Asia, 45, 86, 86, 129
Chacaltaya Glacier, 35, 99
Europe, 129
Latin America, 35, 97, 99, 129-130
observed changes, 19-20, 19-20, 35, 97
projected changes, 28, 43, 129
Grasslands, 58, 62
Greenhouse gas (GHG) emissions
from hydropower dams, 4, 122, 123, 130
water management policies and, 122-124, 123
Groundwater
mitigation measures and, 118
observed changes, 9, 35-36
projected changes, 38-41, 40
salinisation of, 3, 43
H
Health. See Human health
Heatwaves
European (2003), 38
observed changes, 15, 38, 60
projected changes, 24, 26, 95
Helminthiasis, 66, 69
Human health, 67-69
adaptation, vulnerability and sustainable
development, 69
Africa, 80-81, 83
Australia and New Zealand, 91
Europe, 95
Latin America, 96-97, 98-100
North America, 103
observations, 69
projections, 69, 128
small islands, 111
water quality and, 66
Human settlements, 73-74, 128
Hunger, 59
See also Food availability/security
Hydrological cycle
assumptions from past experience, 4
feedbacks with climate, 15, 23-24
projected changes, 3-4, 25-31, 38-48
uncertainties and, 24-25
variability in, 15
See also Hydrology; water entries
196
Hydrology
observed changes, 35-36
projected changes, 38-47
projected impacts on ecosystems and
biodiversity, 55-58
Hydropower, 46, 118, 119, 136
Africa, 82
Europe, 46, 129
greenhouse gas emissions from, 4, 122, 123, 130
infrastructure, 74
North America, 47
See also Dams; Energy
I
Ice
observed changes, 3, 19-20, 19-20
projected changes, 27-28, 130
Ice sheets
contribution to sea-level rise, 20, 24, 28-29
observed changes, 35
Industry, 74-75, 118, 128
Infrastructure, 4, 73-74, 128
Insurance, 74-75, 105
Integrated water resources management
(IWRM), 44, 51, 124
Irrigation
adaptation practices, 63-65, 122, 123, 128
area of irrigated land, 9, 10
greenhouse gas emissions and, 122, 123
water use, observed changes, 8-9
water use, projected changes, 4, 10, 44, 61, 62,
128
K
Kilimanjaro, Mt., 82
L
Lakes
anoxia and algal blooms, 56
chemistry, 36
erosion and sediment, 37
observed changes, 36-37
projected changes, 43, 55-56, 129
thermal structure, 36, 56
Land surface effects, 23-24
Land use, 59-60
adaptation, 64
bio-energy crops and, 117
Index
Land-use change and management, 118, 119-120
Latin America, 96-102, 129-130
adaptation and vulnerability, 50, 100-102, 101
glaciers, 35, 97, 99, 129-130
observed changes, 96-98, 97
pre-Colombian adaptations, 101
precipitation, 16, 97-98
projected changes, 98-100, 129-130
runoff, 21-22, 30, 35
water-stress, 96, 98, 100, 129
Leptospirosis, 97
Linking of climate change and water resources,
33-51
adaptation to climate change, water-related, 48-51
future water changes due to climate change, 38-48
observed climate change impacts, 35-38
See also specific aspects of change and water resources
Livestock, 62, 64
M
Malaria, 80-81, 100
Mekong river, 63
Meningitis, 68
Meridional overturning circulation (MOC), 24
Methane
hydrodams and, 122
landfill/wastewater, 123
sources and sinks, 24, 130
Millennium Development Goals, water sector
and, 131
Mitigation, 115-124, 130
afforestation/reforestation, 118, 120-121
avoided/reduced deforestation, 118, 121
benefits vs. negative side effects of, 4, 67, 130
bio-energy crops, 117-119, 118
biomass electricity, 118, 119
buildings, energy use in, 118, 119
carbon dioxide capture and storage (CCS), 117,
118
cropland drainage, 123, 123
cropland management, 118, 120
desalinisation, 123, 124
future data needs, 136-137
geothermal energy, 118, 119, 123, 124
greenhouse gas (GHG) emissions and, 122-124, 123
hydrodams, 122, 123
hydropower, 118, 119
irrigation, 122, 123
land-use change and management, 118, 119-120
policy implications, 130
relationship with water, 117
residue return, 122-123, 123
synergies with adaptation, 67
unconventional oil, 118, 122
waste/wastewater management, 118, 121, 123-124, 123
water management policies and, 122-124, 123, 130
See also Adaptation
Models. See Climate models
Monsoon regimes, 25
Mountain ecosystems, 58
N
Nasca system of water cropping, 101
New Zealand. See Australia and New Zealand
Nile River, 79, 84
Nitrogen fertiliser use, 10, 120
Non-climatic drivers of water resources, 8, 10, 43-44
North America, 102-106, 130
adaptation, 50, 104-106
case studies of climate change impacts, 104, 105106
droughts, 38, 66
lakes and rivers, thermal structure of, 36
observed change, 102
precipitation, 16
projected change and consequences, 102-104,
102, 130
runoff, 21-22
North Atlantic Oscillation (NAO), 15, 22, 31
O
Observed changes
in climate, 15-23
impacts on water resources, 8-9, 35-38
summary, 3-4
See also specific regions and sectors
Oceans
circulation, climate feedbacks through, 24
salinity, 15, 24
See also Sea-level rise
Oil, unconventional, 118, 122
P
Pastoralist coping strategies, 64
Permafrost. See Frozen ground; Ice
Phenology, 60
197
Index
Polar regions, 106-109, 130
adaptation and vulnerability, 50, 109
observed changes, 107, 108
projected changes, 108-109, 130
Policies
climate change implications for, 125-131
water management, 122-124, 123
See also Adaptation, vulnerability and
sustainable development
Population growth
in coastal areas, 73, 74
water demand and, 4, 8, 9
in water-stressed areas, 45, 45
Precipitation, 15-19, 25-27
anthropogenic contribution to, 16-17
extremes, 26-27, 28
heavy precipitation events, 3, 16-17, 18, 41, 41
heavy precipitation events, costs to agriculture, 61
heavy precipitation events, human health and,
70-71, 128
mean, 25-26
monsoon regimes, 25
observed changes, 3, 15-19, 16-18
projected changes, 3, 25-27, 26-27, 41-42, 41, 127
variability in, 3, 15
See also Cyclones, tropical; Drought
Projected changes
in climate, 9, 24-31
summary, 3-4
in water resources, 9-10, 38-48
See also specific regions and sectors
R
Rangelands, 62
See also Grasslands
Reforestation, 4, 59, 118, 120-121
Regional impacts, 77-113, 128-129
See also specific regions
Residue return, 122-123, 123
Rivers, 36, 55-56
projected impacts, 56, 57-58
river discharge, 45-46, 57-58
See also Runoff
Runoff
mitigation measures and, 118
observed changes, 3, 21-22, 35-36, 37
planning for use of, 71
projected changes, 3, 27, 29-30, 30, 61, 61, 127
198
S
Salinisation
of coastal waters, 57
of groundwater, 3, 43, 71
See also Desalinisation
Sanitation. See Human health
Savannas, 58
Scenarios, 9-10, 10
See also Climate models
Schistosomiasis, 68-69, 97
Sea-level rise
contributions to, 20, 28-29
observed changes, 20
projected changes and impacts, 3, 28-29, 43
water quality and, 10, 43
Semi-arid areas. See Arid and semi-arid areas
Settlements and infrastructure, 73-74, 128
Small islands, 109-113, 130
adaptation, 50, 110, 111-113
observed changes and projections, 109-111, 112, 130
water stress, 130
Snow cover
feedbacks on climate, 23-24
observed changes, 3, 19, 19-20, 35
projected changes, 27-28
Socio-economic aspects of freshwater, 45-47, 74-75
Soil erosion, 43, 57
Soil moisture
feedbacks, 23
observed changes, 21
projected changes, 27, 29
South America. See Latin America
SRES scenarios, 9, 10, 24
Storylines, 9, 10
Sustainable development, 125-131
future climate change impacts threatening, 47, 130
Millennium Development Goals, water sector, 131
rural communities and water conflicts, 66
See also Adaptation, vulnerability and
sustainable development
T
Tar sands, 118, 122
Teleconnections, 22
Temperature
observed changes, 15
projected changes, 24, 31
Thermokarst development, 57
Index
Tourism, 35, 74-75
Transportation, 73-75
Tropical cyclones. See Cyclones, tropical
Tsho Rolpa Risk Reduction Project, 89
U
Uncertainty, 11, 11
See also Gaps in knowledge
V
Variability, large-scale patterns of, 22-23, 31
Vector-borne diseases, 68-69
Vulnerabilities: water resources, 3-4, 9, 47, 47
See also Adaptation, vulnerability and
sustainable development; Water stress
W
Waste, 118, 121, 123
Wastewater reuse, 10
Wastewater treatment, 9, 72
greenhouse gas emissions and, 123-124, 123
mitigation measures and, 118, 121
water quality and, 10
Water availability
mitigation measures and, 118
observations, 69, 70
projections, 44, 70-71
Water-borne diseases, 68, 70, 81, 103
Water chemistry, 36, 37
Water demand
for irrigation, projected, 4, 10, 61, 62, 128
population and, 4, 8, 9
projected changes, 4, 38-47, 44-45
Water management
adaptation practices, 48-51, 49-50
adaptive management, 51
in agriculture, 63-67
assumptions from past experience, 4
climate change and, 4, 43-44, 127
greenhouse gas emissions and, 117
impacts on other areas, 4, 43-44, 47
integrated water resources management
(IWRM), 44, 51, 124
policies, effects on GHG emissions and
mitigation, 122-124, 123
scenario-based approach, 51
See also Adaptation
Water quality
adaptation and, 71-72
drinking water, 45, 67-68, 72
flow variation and, 70-71
micro-pollutants, 10
mitigation measures and, 118
observed changes, 9, 36-37
projected changes, 3, 10, 43, 66, 70-72
temperature and, 71
Water resources
adaptation, overview, 48-51, 49-50
administration of, 72, 127
climate-related drivers, 24-31, 38-43
conflicts, potential, 124
feedbacks with climate, 23-24
highly vulnerable areas and sectors, 47, 47
importance of, 7
linking to climate change, 33-51
mitigation measures and (see Mitigation)
non-climatic drivers, 8, 10, 43-44
observed impacts of climate change, 35-38
projected impacts of climate change, 38-47
summary, 3-4
uncertainties in projected impacts, 47-48
See also Vulnerabilities; Water resources:
regional aspects; and specific water resources
Water resources: regional aspects
Africa, 80, 81-82
Asia, 85-88
Australia and New Zealand, 91
Europe, 93-95
Latin America, 96, 98
North America, 102-104, 102
small islands, 110, 110
Water storage
behind dams, 10
in glaciers and snow cover, 3
Water stress
Africa, 83, 129
definition of, 8
Europe, 129
future impacts of climate change on, 45, 45
Latin America, 96, 98, 100, 129
map of, 9
in small islands, 130
vulnerability and, 8
Water supply and sanitation, 69-73
adaptation, vulnerability and sustainable
development, 4, 71-73
199
Index
observations, 69, 70
projections, 70-71
Water temperature
mitigation measures and, 118
observed changes, 36, 37
projected changes, 127
Water use
200
observed changes, 8-9
projected changes, 43-44, 62
Water vapour
observed changes, 16, 18-19
projected changes, 25-26, 29
Watershed management, 66-67
Wetlands, 56-57, 119
Climate change
and water
O
bservational records and climate projections provide abundant evidence that freshwater resources
are vulnerable and have the potential to be strongly impacted by climate change, with wide-ranging
consequences for human societies and ecosystems.
The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws
together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of
climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality,
use and management. It takes into account current and projected regional key vulnerabilities, prospects for
adaptation, and the relationships between climate change mitigation and water. Its objectives are:
Text in the Technical Paper carefully follows the text of the underlying IPCC Reports, especially the Fourth
Assessment. It reflects the balance and objectivity of those Reports and, where the text differs, this is with the
purpose of supporting and/or explaining further the conclusions of those Reports. Every substantive paragraph
is sourced back to an IPCC Report.
The Intergovernmental Panel on Climate Change (IPCC) was set up jointly by the World Meteorological
Organization and the United Nations Environment Programme to provide an authoritative international assessment
of scientific information on climate change. Climate Change and Water is one of six Technical Papers prepared
by the IPCC to date. It was prepared in response to a request from the World Climate Programme – Water and
the International Steering Committee of the Dialogue on Water and Climate.
climate change and water
• To improve understanding of the links between both natural and anthropogenically induced climate change,
its impacts, and adaptation and mitigation response options, on the one hand, and water-related issues, on
the other;
• To communicate this improved understanding to policymakers and stakeholders.
IPCC Technical Paper VI
Intergovernmental Panel on Climate Change
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