Geoscience Reference
In-Depth Information
2011). In North American mountains, it was observed that a large number of
glaciers were continuously retreating and thinning, and the unconsolidated
and unstable sediment is exposed and mobilized into rivers, which causes
aggradation downstream. As a result, the rate of sedimentation in most of
the river-beds has increased from 7-13 cm up to 1.8 m per decade leading
to more frequent catastrophic shifts in the courses of river channels (ASPEN
International Mountain Foundation 2012).
The glaciers have been found retreating in all Andean countries over
the last three decades with the complete disappearance of a large number
of glaciers. The average rate of retreat of glaciers in Cordillera Blanca of
Peru has been observed to be 26% between 1970 and 2003, in Ecuador 27%
during 1997-2006, 87% reduction in the Mérida Cordillera in Venezuela
in the last 50 years, and 2 to 5% annual decrease in glaciers in Colombia
over the last 10 years. The annual rate of contribution to sea-level rise from
the Patagonian ice-fi elds has doubled during 2000-2005 in comparison to
1975-2000. The area of small glaciers has reduced by 50% in the Argentinean
Tierra del Fuego. The Northern Patagonian Ice Field in South America lost
nearly 140 km² of its snow covered area during 1942 and 2001.
These observed changes in the cryosphere are transforming the
hydrological regimes of mountain headwaters and disrupting drainage
systems all across the basins. Consequently, the regime of water resources in
mountain headwaters is likely to change rapidly, with respect to discharge,
volumes and availability (Tiwari 2000, 2008, Tiwari and Joshi 2012a, 2005,
Bandyopadhyay et al. 2002, Viriroli et al. 2003). In the Himalaya, as many as
35% of the present glaciers will disappear and runoff will increase with peak
fl ow attaining between 2030 and 2050 with a projected temperature increase
of 2ºC by 2050 (Qin 2002). The impacts of retreating glaciers on river-fl ow is
expected to be greater, in small, more highly glaciated headwaters in both
the western and eastern Himalayan mountains under the uniform warming
scenario of +0.06ºC per year. Water discharge in most of the glacier-fed sub-
catchments (glaciation ≥50%) is likely to attain peak fl ow of 150 and 170%
of initial fl ow around 2050 and 2070 in the western and eastern Himalayan
ranges respectively before decreasing until the respective glaciers vanish in
2086 and 2109 (Rees and Collins 2006). The western Himalayan glaciers are
expected to retreat in the next 50 years causing increase of Indus River fl ows,
and then the glacial water-reservoirs will be empty, resulting in decrease of
fl ows by up to 30 to 40% over the subsequent 50 years (World Bank 2005). At
the same time, a large number of mountain communities have been severely
threatened by the diminishing or disappearance of the small ice-masses and
snow fi elds on which they depend for their water supplies (ICIMOD 2007).
It is most likely that most of the mountain regions and their lowlands face a
catastrophic water scarcity by the 2050s resulting from population growth,
climatic change and the increase of water demand (Oki 2003).
Search WWH ::




Custom Search