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Continued from previous page
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). |
 |
| |
Assessment
|
Forecast
|
| |
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. |
|