Thursday, May 10, 2007

"Melting glaciers: Flood of troubles"

From the Times of India:

It's not just the Gangotri glacier that is receding. Actually, thousands of Himalayan glaciers are shrivelling up in varying degrees. The Pindari glacier is receding by 23 metres a year, Bara Shigri by 36 metres a year, Dokriani by 18 metres, Meola by 35 metres, Sonapani by 17 metres, Milam by 13 metres, Zemu by 28 metres - to name just a few.

Cumulatively, this melt could change the way we know our world. If global warming isn't arrested, rivers will first flood and then dry up; seas will rise and fertile lands will turn barren.

Until recently, such talk seemed the prattle of doomsayers. No longer. The devastating impact of melting snows, rising seas and drying rivers is virtually upon us. Within the lifetime of many of us, the Ganga could be a pale shadow of its current glory; shoreline cities and towns, including Mumbai, could be compelled to build dykes to keep out the invading seas; agricultural yield in the fecund Gangetic plains could become insufficient to feed our billion-plus population. That is, unless we act now.

Here's how the disaster scenario could pan out. As temperatures rise, glaciers will melt faster and receive less snowfall. Snowfall in the upper reaches of the glacier adds weight on top, and the pace of melt at its mouth creates a delicate balance, keeping the ice mass in place. When this balance is upset, the glacier either recedes or comes forward dramatically or simply bursts. Any which way, it's a calamity.

At one level, accelerated glacial melt will initially cause excess discharge of water in the rivers. A study has been done on the behaviour of 100 Himalayan rivers. As an illustration, let's take the Ganga. At Uttarkashi, the river level is expected to rise 20-30% within the first two decades and then gradually recede to 50% of its original level over the next decade, signaling that the river is drying up.

Glaciers cover nearly 38,000 sq km of the Himalayan mountains which, in turn, accounts for 800 cubic km of water flow annually. This nurtures the great Indian civilisation as we know it.

Rapid melt of this snow mass is expected to cause floods initially. But within two decades - by 2030, to be precise - when glaciers would have significantly melted, the situation is expected to reverse and several rivers will become a mere trickle.

The impact of this on agriculture is apparent - the lack of water will reduce arable land and that, in turn, will have an adverse affect on our food security.

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