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The Changing Himalayas
There is a major need for more research on Himalayan a substantial influence on glaciers and may have triggered
precipitation processes, as most studies have excluded the glacial surges (Hewitt 2005).
Himalayan region due to the region’s extreme, complex
topography and lack of adequate rain-gauge data (Shrestha
Runoff over Time and Space
et al. 2000).
Mountain regions provide more than 50% of the global river
runoff, and more than one-sixth of the Earth’s population
Glacial Retreat
relies on glaciers and seasonal snow for their water supply.
Himalayan glaciers are receding faster today than the world The effects of climatic change are of tremendous importance
average (Dyurgerov and Meier 2005) (Figure 3). In the to the often densely populated lowland regions that depend
last half of the 20
Century, 82% of the glaciers in western on mountain water for their domestic, agricultural, and
China have retreated (Liu et al. 2006). On the Tibetan industrial needs (e.g., Barnett et al. 2005; Graham et
Plateau, the glacial area has decreased by 4.5% over al. 2007). The processes that determine the conversion
the last twenty years and by 7% over the last forty years of precipitation into runoff and downstream flow are
(CNCCC 2007) indicating an increased retreat rate. (Ren many and complex. Changes in precipitation type (rain,
et al. 2003). Glacier retreat in the Himalayas results from snow) and its amount, intensity, and distribution over time
“precipitation decrease in combination with temperature and space has a direct impact on total and peak river
increase. The glacier shrinkage will speed up if the climatic runoff, potentially moving it away from agricultural and
warming and drying continues” (Ren et al. 2003). dry season demands and towards monsoon flash floods.
Evapotranspiration rates, linked to temperature, have an
The IPCC Fourth Assessment Report (IPCC, 2007a; 2007b)
effect on the amount of water available for runoff. However,
states that there is a high measure of confidence that in the
one of the main concerns in relation to climate change in
coming decades many glaciers in the region will retreat,
the Himalayan region is the reduction of snow and ice,
while smaller glaciers may disappear altogether. Various
which reduces the water storage capacity. Initially, it is
attempts to model changes in the ice cover and discharge
likely that the stable base-flow – derived from melting ice
of glacial melt have been made by assuming different
and snow – will increase, particularly during warm and dry
climate change scenarios. One concludes that with a
seasons. It is not unlikely that this will appear as a positive,
2ºC increase by 2050, 35% of the present glaciers will
comforting sign, deterring and delaying required emergency
disappear and runoff will increase, peaking between 2030
initiatives. However, as the far-away and high-altitude
and 2050 (Qin, 2002).
reservoirs of snow and ice continue to decrease, eventually
Retreat in glaciers can destabilise surrounding slopes and
disappearing, the variability of downstream runoff will
may give rise to catastrophic landslides (Ballantyne and
increase, potentially dramatically, and progressively reflect
Benn 1994; Dadson and Church 2005), which can dam
direct rainfall-runoff, which in turn will mirror precipitation
streams and sometimes lead to outbreak floods. Excessive
and evapotranspiration rates.
meltwaters, often in combination with liquid precipitation,
In Asia, climate change induced glacial melt could seriously
may trigger flash floods or debris flows. In the Karakoram,
affect half a billion people in the Himalayan region overall
there is growing evidence that catastrophic rockslides have
and a quarter of a billion people in China, who all depend
on glacial melt for their water supply (Stern 2007). In South
Asia, hundreds of millions of people depend on perennial
rivers such as the Indus, Ganges, and Brahmaputra – all
Figure 3: Rapid retreat of greater Himalayan glaciers
in comparison to the global average
fed by the unique water reservoir formed by the 16,000
(Source: Dyurgerov and Meier 2005) Himalayan glaciers. The current trends in glacial melt
suggest that the low flow will become substantially reduced
as a consequence of climate change (IPCC 2007a).
The effect of this on, for example, food production and
Alps economic growth is likely to be unfavourable. The situation
may appear to be normal in the region for several decades
to come, and even with increased amounts of water
available to satisfy dry season demands. However, when
the shortage arrives, it may happen abruptly, with water
Tian Shan
Baffin Island
systems going from plenty to scarce in perhaps a few
Cumulative mass balance, m
decades or less. Some of the most populated areas of the
Alaska Range world may “run out of water during the dry season if the
current warming and glacial melting trends continue for
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