Synthesis Report - Question 8

Climate Change 2001: Synthesis Report

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Table 8-2: Examples of regional impacts of climate change on water resources, land degradation, and desertification.
Region Projections
Reference Section in WGII TAR
Africa Changes in rainfall and intensified land use would exacerbate the desertification processes.
Desertification would be exacerbated by reduction in the average annual rainfall, runoff, and soil moisture in countries of west African Sahel, and northern and southern Africa (medium confidence).
Increases in droughts and other extreme events would add to stresses on water resources, food security, and human health, and would constrain development in the region (high confidence).
TS 5.1.6, Chapter 10 ES, Sections 10.2.1 & 10.2.6, & Table SPM 2
Asia Water shortage -- already a limiting factor for ecosystems, food and fiber production, human settlements, and human health -- may be exacerbated by climate change. Runoff and water availability may decrease in arid and semi-arid Asia but increase in northern Asia (medium confidence). Reduced soil moisture in summer would exacerbate land degradation and desertification in arid and semi-arid regions. TS 5.2.3 & Sections 11.1.1 & 11.2.3
Australia and New Zealand Interannual variability due to ENSO leads to major floods and droughts in Australia and New Zealand. Such variations are expected to continue under enhanced greenhouse gas conditions, but possibly with greater hydrological extremes.
Water is likely to be a key issue (high confidence) due to projected drying trends over much of the region and change to a more El Niño-like event state. Water quality would be affected, and more intense rainfall events would increase fast runoff, soil erosion, and sediment loading. Eutrophication is a major water quality problem in Australia.
TS 5.3 & Sections & 12.3
Europe Summer runoff, water availability, and soil moisture are likely to decrease in southern Europe, and would widen the gap between the north and south (high confidence). Flood hazards will increase across much of Europe (medium to high confidence); risk would be substantial for coastal areas where flooding will increase erosion and result in loss of wetlands. Half of alpine glaciers and large permafrost areas could disappear by the end of the 21st century (medium confidence).
TS 5.4.1, Chapter 13 ES, & Section 13.2.1
Latin America Some studies based on model experiments suggest that under climate change the hydrological cycle would be more intense, with changes in the distribution of extreme rainfall, wet spells, and dry spells. Frequent severe drought in Mexico during the last decade coincides with some of these model findings. El Niño is related to dry conditions in northeastern Brazil, northern Amazons, and the Peruvian-Bolivian altiplano. Southern Brazil and northwestern Peru exhibit anomalous wet conditions during these periods.
Loss and retreat of glaciers would adversely impact runoff and water supply in areas where snowmelt is an important water resource (high confidence).
TS 5.5.1, Chapter 14 ES, & Section 14.2.4
North America Snowmelt-dominated watersheds in western North America will experience earlier spring peak flows (high confidence) and reduction in summer flow (medium confidence); adaptive responses may offset some, but not all, of the impacts on water resources and aquatic ecosystems (medium confidence). TS 5.6.2, Section 15.2.1, & Table SPM-2
Small Islands Islands with very limited water supplies are highly vulnerable to the impacts of climate change on the water balance (high confidence). TS 5.8.4, Section 17.2.6, & Table SPM-2

  Freshwater and Climate Change

8.19 All three classes of freshwater problems -- having too little, too much, and too dirty water -- may be exacerbated by climate change. Freshwater is essential for human health, food production, and sanitation, as well as for manufacturing and other industrial uses and sustaining ecosystems. There are several indicators of water resources stress. When withdrawals are greater than 20% of the total renewable resources, water stress often is a limiting factor on development. Withdrawals of 40% or more represent high stress. Similarly, water stress may be a problem if a country or region has less than 1,700 m 3 yr-1 of water per capita. In the year 1990, approximately one-third of the world's population lived in countries using more than 20% of their water resources, and by the year 2025 about 60% of a larger total would be living in such a stressed country, only because of population growth. Higher temperatures could increase such stress conditions. However, adaptation through appropriate water management practices can reduce the adverse impacts. While climate change is just one of the stresses on water resources in this increasingly populated world, it is clear that it is an important one (see Table 8-2). The TAR projections using the SRES scenarios of future climate indicate a tendency for increased flood and drought risks for many areas under most scenarios. Decreases of water availability in parts of a warmer world are projected in areas like southern Africa and countries around the Mediterranean. Because of sea-level rise, many coastal systems will experience saltwater intrusion into fresh groundwater and encroachment of tidal water into estuaries and river systems, with consequential effects on freshwater availability.

WGII TAR Sections 4.1, 4.4.3, 4.5.2, & 4.6.2
8.20 Water managers in some countries are beginning to consider climate change explicitly, although methodologies for doing so are not yet well defined. By its nature, water management is based around minimization of risks and adaptation to changing circumstances, now also changing climate. There has been a gradual shift from "supply-side" approaches (i.e., providing water to satisfy demands by increased capacity reservoirs or structural flood defenses) towards "demand-side" approaches (i.e., trimming demands adequately to match water availability, using water more efficiently, and non-structural means of preparedness to floods and droughts). WGII TAR Section 4.2.4

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