3 Freshwater resources and their management Coordinating Lead Authors: Zbigniew W. Kundzewicz (Poland), Luis José Mata (Venezuela) Lead Authors: Nigel Arnell (UK), Petra Döll (Germany), Pavel Kabat (The Netherlands), Blanca Jiménez (Mexico), Kathleen Miller (USA), Taikan Oki (Japan), Zekai Senç (Turkey), Igor Shiklomanov (Russia) Contributing Authors: Jun Asanuma (Japan), Richard Betts (UK), Stewart Cohen (Canada), Christopher Milly (USA), Mark Nearing (USA), Christel Prudhomme (UK), Roger Pulwarty (Trinidad and Tobago), Roland Schulze (South Africa), Renoj Thayyen (India), Nick van de Giesen (The Netherlands), Henk van Schaik (The Netherlands), Tom Wilbanks (USA), Robert Wilby (UK) Review Editors: Alfred Becker (Germany), James Bruce (Canada) This chapter should be cited as: Kundzewicz, Z.W., L.J. Mata, N.W. Arnell, P. Döll, P. Kabat, B. Jiménez, K.A. Miller, T. Oki, Z. Senç and I.A. Shiklomanov, 2007: Freshwater resources and their management. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 173-210. Freshwater resources and their management Chapter 3 Table of Contents .....................................................175 3.5.2 How will climate change affect flood Executive summary damages?...............................................................196 .......................................................175 3.1 Introduction 3.6 Adaptation: practices, options and ...................176 ...........................................................196 3.2 Current sensitivity/vulnerability constraints 3.6.1 The context for adaptation....................................196 ..................180 3.3 Assumptions about future trends 3.6.2 Adaptation options in principle .............................197 3.3.1 Climatic drivers.......................................................180 Box 3.2 Lessons from the ‘Dialogue on Water and 3.3.2 Non-climatic drivers ...............................................181 Climate’ .................................................................197 3.6.3 Adaptation options in practice ..............................198 .......182 3.4 Key future impacts and vulnerabilities 3.6.4 Limits to adaptation and adaptive capacity..........199 3.4.1 Surface waters .......................................................182 3.6.5 Uncertainty and risk: decision-making 3.4.2 Groundwater ..........................................................185 under uncertainty ..................................................199 3.4.3 Floods and droughts ..............................................186 3.4.4 Water quality ..........................................................188 3.7 Conclusions: implications for sustainable ........................................................200 3.4.5 Erosion and sediment transport.............................189 development 3.8 Key uncertainties and research ......190 ..............................................................201 3.5 Costs and other socio-economic aspects priorities 3.5.1 How will climate change affect the balance ......................................................................202 of water demand and water availability? ...............191 References Box 3.1 Costs of climate change in Okanagan, Canada ...195 174 Chapter 3 Freshwater resources and their management Executive summary Adaptation procedures and risk management practices for the water sector are being developed in some countries and regions (e.g., Caribbean, Canada, Australia, Netherlands, The impacts of climate change on freshwater systems and UK, USA, Germany) that have recognised projected their management are mainly due to the observed and hydrological changes with related uncertainties (very high projected increases in temperature, sea level and confidence). precipitation variability (very high confidence). Since the IPCC Third Assessment, uncertainties have been More than one-sixth of the world’s population live in glacier- or evaluated, their interpretation has improved, and new methods snowmelt-fed river basins and will be affected by the seasonal (e.g., ensemble-based approaches) are being developed for their shift in streamflow, an increase in the ratio of winter to annual characterisation (very high confidence) [3.4, 3.5]. Nevertheless, flows, and possibly the reduction in low flows caused by quantitative projections of changes in precipitation, river flows, decreased glacier extent or snow water storage (high confidence) and water levels at the river-basin scale remain uncertain (very [3.4.1, 3.4.3]. Sea-level rise will extend areas of salinisation of high confidence) [3.3.1, 3.4]. groundwater and estuaries, resulting in a decrease in freshwater The negative impacts of climate change on freshwater availability for humans and ecosystems in coastal areas (very systems outweigh its benefits (high confidence). high confidence) [3.2, 3.4.2]. Increased precipitation intensity and variability is projected to increase the risks of flooding and All IPCC regions (see Chapters 3–16) show an overall net drought in many areas (high confidence) [3.3.1]. negative impact of climate change on water resources and freshwater ecosystems (high confidence). Areas in which runoff Semi-arid and arid areas are particularly exposed to the is projected to decline are likely to face a reduction in the value impacts of climate change on freshwater (high confidence). of the services provided by water resources (very high Many of these areas (e.g., Mediterranean basin, western USA, confidence) [3.4, 3.5]. The beneficial impacts of increased southern Africa, and north-eastern Brazil) will suffer a decrease annual runoff in other areas will be tempered by the negative in water resources due to climate change (very high confidence) effects of increased precipitation variability and seasonal runoff [3.4, 3.7]. Efforts to offset declining surface water availability shifts on water supply, water quality, and flood risks (high due to increasing precipitation variability will be hampered by confidence) [3.4, 3.5]. the fact that groundwater recharge will decrease considerably in some already water-stressed regions (high confidence) [3.2, 3.1 Introduction 3.4.2], where vulnerability is often exacerbated by the rapid increase in population and water demand (very high confidence) [3.5.1]. Water is indispensable for all forms of life. It is needed in almost all human activities. Access to safe freshwater is now Higher water temperatures, increased precipitation regarded as a universal human right (United Nations Committee intensity, and longer periods of low flows exacerbate many on Economic, Social and Cultural Rights, 2003), and the forms of water pollution, with impacts on ecosystems, Millennium Development Goals include the extended access to human health, water system reliability and operating costs safe drinking water and sanitation (UNDP, 2006). Sustainable (high confidence). management of freshwater resources has gained importance at These pollutants include sediments, nutrients, dissolved organic regional (e.g., European Union, 2000) and global scales (United carbon, pathogens, pesticides, salt, and thermal pollution [3.2, Nations, 2002, 2006; World Water Council, 2006), and 3.4.4, 3.4.5]. ‘Integrated Water Resources Management’ has become the corresponding scientific paradigm. Climate change affects the function and operation of Figure 3.1 shows schematically how human activities affect existing water infrastructure as well as water management freshwater resources (both quantity and quality) and their practices (very high confidence). management. Anthropogenic climate change is only one of many Adverse effects of climate on freshwater systems aggravate the pressures on freshwater systems. Climate and freshwater impacts of other stresses, such as population growth, changing systems are interconnected in complex ways. Any change in one economic activity, land-use change, and urbanisation (very high confidence) [3.3.2, 3.5]. Globally, water demand will grow in the coming decades, primarily due to population growth and increased affluence; regionally, large changes in irrigation water demand as a result of climate change are likely (high confidence) [3.5.1]. 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 (very high confidence) [3.4, 3.5]. Improved incorporation of current climate variability into water-related Figure 3.1. Impact of human activities on freshwater resources and management would make adaptation to future climate change their management, with climate change being only one of multiple pressures (modified after Oki, 2005). easier (very high confidence) [3.6]. 175 Freshwater resources and their management Chapter 3 of these systems induces a change in the other. For example, the water resources and related vulnerabilities are presented (Section draining of large wetlands may cause changes in moisture 3.4) as well as the impacts on water-use sectors (Section 3.5). recycling and a decrease of precipitation in particular months, Please refer to Chapter 1 for further information on observed when local boundary conditions dominate over the large-scale trends, to Chapter 15 (Sections 15.3 and 15.4.1) for freshwater