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and 33,050 km
2
respectively (Dyurgerov and Meir 2005). Climatically, the
northern slope of Himalaya is cold and dry, and southern slope warm and
moist, indicating a general decrease, from south to north, in precipitation
and temperature. The topography of the Himalaya-Tibetan plateau, which
acts as an elevated heat source, is crucial to the onset of the monsoon,
and sets this region apart from some other tropical/sub-tropical regimes
(Webster et al. 1998). Broadly, the major controls on climate in the region
are latitude, altitude and position relative to the Indian monsoon fl ow.
Summer monsoon or Southwestern monsoon is critical in controlling
regional climate. Upon reaching the Himalaya by late June monsoon air rises
and cools, the moisture condenses and heavy precipitation ensues. It also
penetrates into Southeast Tibet by moving along the Brahmaputra valley.
There are some 24,488 glaciers that spread across mountains of Southwestern
China, which includes the Himalaya and the Nyainqntanglha, Tanggula
and Hengduan mountains. Together they make up an area of almost 30,000
square kilometers. According to (Zongxing Li et al. 2011) climate change has
had devastating affects on glaciers of mountains of Southwestern China.
Their data shows that between 1970 and 2001, the Penggu basin's 999
glaciers lost a combined surface area of 131 square kilometers and 12 cubic
kilometers of mass. The Gangrigabu Mountains also showed signifi cant
losses. There, 102 glaciers disappeared between 1915 and 1980, equaling a
loss of more than 41 square kilometers in area and six cubic kilometers in
mass. The Yalung glacier alone receded more than 1,500 meters between
1980 and 2001, resulting of swelling of nearby glacier lakes. The three major
South Asian river basins provide water to more than 1.5 billion people vary
considerably in characteristics (Table 13.1). The Indus and Brahmaputra
have extensive upstream areas (>2000 m) and larger glaciated areas. All
support large-scale irrigation system and thousands of ecosystem and play
a crucial role in sustaining human populations. During last 30 years a large
number of glaciers in warm and humid valleys of south of Himalayan arc
Table 13.1.
Characteristics of the three major south Asian rivers.
All in %
Indus
Ganga
Brahmaputra
Snow & Glacier Melt in total Q
44.8
9.1
12.3
Upstream Area > 2000 m in %
40
14
68
Glaciated Area in %
2.2
1.0
3.1
Upstream ppt.
> 2000 m in %
Downstream ppt.
36
11
89
40
60
64
NMI: Upstream Q
/Downstream Q
(NMI=index)
151
10
27
Source:
Science
, v. 328, 2010
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