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Thursday, October 18, 2012

retreating glaciers unlikely to change water availability water availability

Even though scientific evidences show that most glaciers in South Asia’s Hindu Kush Himalayan region are retreating, the consequences for the region’s water supply is unclear

Retreating glaciers is unlikely to cause significant changes in water availability at lower elevations over the next several decades but other factors including ground water depletion and increasing human water use could have greater impact.
This is the latest finding from a new report called the “Himalayan Glaciers: Climate Change, Water Resources, and Water Security” published by the National Research Council, USA.
The report examines how changes to glaciers in the Hindu Kush Himalayan region, which covers eight countries across Asia, could affect the area’s river systems, water supplies, and the South Asian population.
The committee that wrote the report said the entire Himalayan climate is changing but how climate change will impact specific places remains unclear.
“While glacier melt contributes water to the region’s rivers and streams, retreating glaciers over the next several decades are unlikely to cause significant change in water availability at lower elevations, which depend primarily on monsoon precipitation and snowmelt,” said the committee.
However, higher elevation areas could experience altered seasonal and temporal water flow in some river basins if current rates of glacial retreat continue.
The report suggests that glacier melt water contributes less to the Hindu Kush Himalayan region’s water supply than previously though.
A modeling showed that in Nepal, the glacial melt water contribution to tributaries to the Ganges varies from approximately 20% in the Budhai Gandaki basin to approximately 2% in the Likhu Khola basin.
Glacial melt water can act as a buffer against the hydrologic impacts of a changing climate, such as drought. For example, during the 2003 European drought glacial melt water from the Alps contributed about three times more water to the Danube River than the 100 year average.
“Water stored as glacial ice could serve as the Himalayan region’s hydrologic insurance and although retreating glaciers would provide more melt water in the shorter term as glaciers shrink, the loss of glacier insurance could become problematic over the longer term.
There are concerns that increased melt water generated as glaciers retreat could cause flooding in downstream communities.
“Although it is unlikely that glacial retreat in the Hindu Kush Himalayan region would lead to flows of water large and rapid enough to cause flooding, the region does face other physical hazards,” states the report.
The physical hazards include flash flooding due to extreme precipitation, flooding due to monsoon rainfall, and flooding that is caused when water dammed by a glacier or sediment is rapidly released due to failure of the dam.
The mountains in the region form the water towers of several major river systems including the Ganges, Mekong, Yangtze, and Yellow river which serve as sources of drinking water and irrigation supplies for roughly 1.5bn people.
The report also makes recommendations and sets guidelines for the future of climate change and water security in the Himalayan region.
To implement adaptive management techniques, it will be necessary to monitor the impacts of water management policies and make adjustments as required.
The capacity of governments and institutions to adapt to climate change will vary across the region.
“This means it will be important to expand monitoring programs that gather information on glacier mass balances, stream flow, and water quality in the Hindu Kush Himalayan region,” states the report.

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