Working Group II: Impacts, Adaptation and Vulnerability

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An assessment of implications of climate change for global hydrological regimes and water resources, using climate change scenarios developed from Hadley Centre model simulations (Arnell, 1999), allows examination of the potential impacts on Asia. A macro-scale hydrological model was used to simulate river flows across the globe at a spatial resolution of 0.5°x0.5°, covering regions of 1,800-2,700 km2. The study suggests that average annual runoff in the basins of the Tigris, Euphrates, Indus, and Brahmaputra rivers would decline by 22, 25, 27, and 14%, respectively by the year 2050. Runoff in the Yangtze (Changjiang) and Huang He Rivers have the potential to increase as much as 37 and 26%, respectively. Increases in annual runoff also are projected in the Siberian rivers: the Yenisey (15%), the Lena (27%), the Ob (12%), and the Amur (14%). Areas with particularly large percentage change in high flows include temperate Asia. Significant changes in monthly runoff regimes also are projected over most of Asia.

Some areas of the Asian continent are expected to experience increases in water availability; other areas will have reduced water resources available. Surface runoff is projected to decrease drastically in arid and semi-arid Asia under climate change scenarios and would significantly affect the volume of water available for irrigation and other purposes. Sensitivity analysis of water resources in Kazakhstan to projected climate change scenarios indicates that surface runoff would be substantially reduced as a result of an increase in surface air temperature of 2°C accompanied by a 5-10% decline in precipitation during summer (Gruza et al., 1997). In temperate Asia, future changes in surface runoff would be highly spatially inhomogeneous. An increase in surface runoff seems likely in Mongolia and northern China. The hydrological characteristics of Japanese rivers and lakes also are sensitive to climate change. Recent studies suggest that, on average, a 3°C increase in temperature coupled with a 10% increase in precipitation will increase river flows by approximately 15% in water-abundant areas. An increase in temperature also accelerates snow melting, which increases river flows from January through March but decreases flows from April through June (Hanaki et al., 1998; Inoue and Yokoyama, 1998).

The perennial rivers originating in the high Himalayas receive water from snow and glaciers. Snow, ice, and glaciers in the region are approximately equivalent to about 1,400 km3 of ice. The contribution of snow to the runoff of major rivers in the eastern Himalayas is about 10% (Sharma, 1993) but more than 60% in the western Himalayas (Vohra, 1981). Because the melting season of snow coincides with the summer monsoon season, any intensification of the monsoon is likely to contribute to flood disasters in Himalayan catchments. Such impacts will be observed more in the western Himalayas compared to the eastern Himalayas because of the higher contribution of snowmelt runoff in the west (Sharma, 1997). An increase in surface runoff during autumn and a decrease in springtime surface runoff are projected in highland regions of south Asia. The increase in surface temperature also will contribute to a rise in the snowline—which, in effect, reduces the capacity of the natural reservoir. This situation will increase the risk of flood in Nepal, Bangladesh, Pakistan, and north India during the wet season (Singh, 1998). No significant changes are projected for annual mean surface runoff in southeast Asia; an increase during winter and a decrease during summer season is likely, however.

Available data on the dynamics of freshwater use by natural-economic regions of Asia (Table 11-8) suggest that freshwater use—in terms of total water withdrawal and water consumption— have increased significantly in recent decades in all regions and is projected to increase further in the 21st century. Table 11-8 also suggests that water use in most regions of Asia (except Russia and southeast Asia) already has exceeded 20% of the available resources (Arnell, 1999) and will be increasing appreciably by 2025. It follows from this table that water is going to be a scarce commodity in Asia in the near future even without the threat of climate change.

Table 11-8: Dynamics of freshwater use in Asia over sectors of economic activities, km3 yr-1 (Shiklomanov, 2001).
  1900 1900 1900 1995 2000 2010 2025
Population (million)   1464 2103 3498 3762 4291 4906
Irrigation area (Mha) 36.1 72.5 118 175 182 199 231
Water usea              
- Agriculture 408 408 1331 1743 1794 1925 2245
  320 643 1066 1434 1457 1553 1762
- Industry 4 33 107 184 193 248 409
  1 6 13 30 32 40 58
- Domestic 2 11 38 160 177 218 343
  1 5 14 31 33 36 44
- Reservoirs (evaporation) 0 0.23 23 70 81 92 107
Total 414 860 1499 2157 2245 2483 3104
  322 650 1116 1565 1603 1721 1971
a Nominator = total water withdrawal; denominator = water consumption.
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