Glaciers beating retreat

Himalayan glaciers, source of water for the innumerable rivers that flow across the Indo-Gangetic plains, are receding. And that too at a phenomenal rate. As they continue to recede, incidents of landslides, changes in river regimes and floods will increase. But only while the glaciers last. If global warming is the cause of this decline, then we can expect glaciers to disappear one day. In the long run, with large sections of these glaciers gone, the rivers will dry up. Impacts on the flora and fauna, and the 500 million people inhabiting the great Indian plain are hard to imagine. All we can conjecture today is, a few decades from now, the nation will experience a great thirst

 
Last Updated: Sunday 07 June 2015

Glaciers beating retreat

 The mother of all: Gangotri g On august 4, 1985, a moraine-dammed glacial lake, Dig Tsho, burst in the Khumbu Himal area of Nepal. Within four to six hours, the lake had emptied into Lagmoche valley, one of the tributary valleys of the river Bhote Kosi, which flows along many Sherpa settlements. For more than 90 km, the flood waters -- 10 to 15 metres high -- surged through the valley in the form of a huge "black" mass of debris.

Trees and boulders were dragged and tossed around, causing landslides of varying sizes. Entire trails of the nearly complete Namche Small Hydel Project, 14 bridges and numerous houses that dotted the river disappeared in a few hours.

Swiss scientists Daniel Vuichard and Marcus Zimmermann studied the catastrophe in detail. They concluded that the incident was one of several possible disasters which resulted from the thinning and receding of glaciers.They even warned about the frequency of such outbursts in the Himalaya in the future.

" Glaciers in the Himalaya are receding faster than in any other part of the world and, if the present rate continues, the likelihood of them disappearing by the year 2035 is very high," says the International Commission for Snow and Ice ( icsi ) in its recent study on Asian glaciers. "But if the Earth keeps getting warmer at the current rate, it might happen much sooner," says Syed Iqbal Hasnain of the School of Environmental Sciences, Jawaharlal Nehru University, New Delhi. Hasnain is also the chairperson of the Working Group on Himalayan Glaciology ( wghg ), constituted in 1995 by the icsi.

"The glacier will be decaying at rapid, catastrophic rates. Its total area will shrink from the present 500,000 to 100,000 square km by the year 2035," says former icsi president V M Kotlyakov in the report Variations of snow and ice in the past and present on a global and regional scale (see table: Receding rivers of ice ).

With the end of the Little Ice Age (1430 to 1850), glaciers have been retreating with the rise in atmospheric temperatures. "In the last 100 years alone, the global mean temperature has increased by about 0.5 to 1 c ... and the rapid receding of glaciers, to a major extent, is a consequence of global warming," says Jagdish Bahadur, a leading glaciologist and former joint advisor at the Department of Science and Technology, New Delhi.

Snowblind
In geological terms, the Dig Tsho lake burst was a very recent event. But, despite warnings and several reports of receding glaciers in India, there has been no attempt to study the glaciers that dot the northern and eastern part of the country.

Himalayan glaciers cover about three million hectares or 17 per cent of the mountain area as compared to 2.2 per cent in the Swiss Alps. They form the largest body of ice outside the Polar caps. The 15,000-odd Himalayan glaciers form a unique reservoir which supports mighty perennial rivers such as the Indus, Ganga and Brahmaputra which, in turn, are the lifeline of millions of people. The Gangetic basin alone is home to 500 million people, about 10 per cent of the total human population.

But whenever disaster strikes in the form of floods or landslides, no one thinks beyond the immediate damage control and rescue operation. The tragedy is forgotten by the end of the monsoons. Another year, another string of tragedies follow. There is no effort to study the problem in detail. And policymakers are yet to comprehend the gravity of the problems caused by receding glaciers.

This not only implies more Dig Tsho-like tragedies in the near future. It means more water in the rivers. "But, in the long run, the melting of glaciers also means drying up of rivers," says Hasnain. "Most of the rivers in northern India originate from glaciers. About 70 to 80 per cent of the water in these rivers come from snow and glacial melts, and the rest from monsoonal rains." Does this mean that the Ganga, Indus, Brahmaputra and the innumerable rivers that criss-cross the entire northern Indian plain will become seasonal rivers in the near future? "This is not unlikely," warns Hasnain.

receding rivers of ice
Record of retreat of some glaciers in the Himalaya

Glacier

Period Retreat of Snout (metre) Average retreat of  Glacier (metre/yr)
Triloknath Glacier (Himachal Pradesh) 1969-1995 400 15.4

Pindari Glacier (Uttar Pradesh)

1845-1966 2,840 135.2
Milam Glacier (Uttar Pradesh) 1909-1984 990 13.2
Ponting Glacier (Uttar Pradesh) 1906-1957 262 5.1
Chota Shigri Glacier (Himachal Pradesh) 1986-1995 60 6.7
Bara Shigri Glacier (Himachal Pradesh) 1977-1995 650 36.1
Gangotri Glacier (Uttar Pradesh) 1977-1990 364 28.0
Zemu Glacier (Sikkim) 1977-1984 194 27.7

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