Edmund Hillary and Sherpa Tenzing Norgay were trying today to climb Everest, they would save 5 kilometers of climb on the perilous Khumbu Glacier, which has declined since their feat of 1953. Nicknamed the "water tower of Asia", the Himalayan massif melts its glaciers, under the effect of warming. The World Wide Fund for Nature (WWF), which has gathered three studies on India, Nepal and China, is alarmed, in a report released on March 15.
The Himalayan glaciers, which cover 33 000 km2, feed seven major rivers of Asia: the Ganges, Indus, Brahmaputra, Salween, Mekong, the Yangtze (Blue River) and Huang He (River Yellow). The 8,6 million cubic meters flowing annual summits provide fresh water to millions of people. The accelerated melting of glaciers could mean for them more flooding in first few decades before a shortage ensues.
Hydroelectric power, agriculture, certain industries depend directly on the input of freshwater: the economic impact will be substantial, worries the WWF, calling on the topic of regional cooperation.
Projections show a century for India a contrasting situation in time and space: in the Upper Indus, the flow will increase 14 90% to% in the first decades, before decreasing in the same proportion of by 2100. In the Ganges, the upstream part will experience the same type of variation, while in the most downstream area, where the water supply is primarily due to monsoon rains, the impact of deglaciation will be practically negligible.
These differences are that glacial meltwater is only 5% of the flow of Indian rivers, but it contributes greatly to their regulation, particularly during the dry season. Thus, to the Ganges, loss of glacial meltwater would reduce the rate of two-thirds from July to September, which would mean a shortage of water for millions of people and 500 37% of Indian affect irrigated crops, provides report.
WWF also highlights the increased risks of sudden discharge from glacial lakes. Supercharged because of melting ice, they are indeed more likely to break the natural dikes that contain them. And to cause catastrophic floods below, sometimes for tens of kilometers. On the 229 glaciers identified in the Arun Basin, Tibet, 24 "are potentially dangerous," notes the report.
In China, the basins of the Yangtze and Yellow rivers experiencing a decrease in wetland and lake surfaces. Desertification progresses. The Yellow River could reach the sea during 226 1997 days, a record year.
"All observations agree," confirms Yves Arnaud (IRD, laboratory of glaciology of Grenoble). The topographic and satellite data he himself analyzed show a decrease in the thickness of the Himalayan glaciers ranging from 0,2 m to 1 meter for fifty years ...