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6
Introduction
At the roof of the world, the Tibetan plateau supplies,
together with the Himalayas, Hindu Kush and the Tian
Shan mountain ranges, water to people in Central,
Southern, Western and South-east Asia, the largest
river run-off from any single location in the World
(UNEP, 2002a) (Fig. 1). Major rivers originating from
these mountain regions include the Syr Darya, the Amu
Darya; the Ganges, the Indus, the Arun, The Sankosh,
the Manas, the Yarlung/Brahmaputra, the Chindwin,
the Salween/Nu Jiang, the Lancang Jiang/Mekong, the
Jinsha Jiang, the Huang He and the Yangtze, in addi-
tion to numerous other rivers. While the mountains are
homes to some 170 million people, the water resources
influence the lives of close to half of the world’s popula-
tion downstream. The region comprises unique biodi-
versity, ranging from desert, steppe and high-altitude
fauna to tropical rainforests with global biodiversity
hotspots, such as in South-Western China.
While mountains traditionally have been considered the
major water sources of the region, there is great diver-
sity, particularly between north-western and south-east-
ern regions in the hydrological significance of moun-
tains for water supply further downstream (Viviroli et al.,
2003). For several of the rivers from the Tian Shan and
Hindu Kush into Central Asia and Pakistan, such as the
Amu Darya and the Indus, the mountain sections are
responsible for >90% of the estimated discharge, while
rivers like the Mekong also receive substantial water
from lowland catchments and the monsoons. There is
also extreme variability within this region with regard
to vulnerability to land use patterns, land slides, floods,
drought or glacial outbursts (Semwal et al., 2004; Gau-
tam et al., 2003; Blyth et al., 2002; Gurung and Gurung,
2002; Chettri et al., 2002,; Dongol et al., 2002). In spite
of the vast water supply, water scarcity is a major prob-
lem in the region, both up- and downstream, including
both drinking water and irrigation (Merz et al., 2003).
Desertification is a major problem in north-western parts
of China, such as in parts of Xinjiang, particularly as a
result of intensified land use along road corridors. The
rivers form basic lifelines to people including access to
0
2 000
4 000
6 000
8 000
10 000
14 000
12 000
2 000
4 000
6 000
8 000
10 000
12 000
0
0
2 000
4 000
6 000
8 000
0
2 000
4 000
0
2 000
0
2 000
1920
1930
1940
1950
1960
1970
1980
Asia
South America
North America
Africa
Europe
Australia and Oceania
km
3
per year
Source: Igor A. Shiklomanov, State Hydrological Institute (SHI, St. Petersburg) and United Nations Educational, Scientific and Cultural Organisation (UNESCO, Paris), 1999.
FEBRUARY2002
PHILIPPEREKACEWICZ
River Runoff through the 20th Century
Average Annual Volumes by Continent, 1921-1985
UNEP
Figure 1:
While Asia has the highest share in the run-off of all the World’s rivers, it holds an estimated 60% of the
World’s population (~3, 675,000,000 people in 2000), but only 36% of its river run-off (UNEP, 2002a).