Edmund Hillary and Sherpa Tenzing Norgay were trying today to climb Everest, they would spare themselves 5 kilometers of ascent on the perilous Khumbu glacier, which has receded as much since their feat of 1953. Nicknamed the "castle of “water of Asia”, the Himalayan massif is seeing its glaciers melt, under the effect of warming. The World Wide Fund for Nature (WWF), which brought together three studies on India, Nepal and China, is alarmed, in a report released on March 15.
The glaciers of the Himalayas, which cover 33 km000, feed seven of the main rivers of Asia: the Ganges, the Indus, the Brahmaputra, the Salween, the Mekong, the Yangzi (Blue river) and the Huang He ( Yellow). The 2 million cubic meters that flow from the peaks each year provide millions of people with fresh water. The accelerated melting of glaciers could mean more flooding for them initially ˇ a few decades ˇ, before a shortage ensues.
Hydroelectric power, agriculture, certain industries depend directly on the supply of fresh water: the economic impact will therefore be substantial, worries the WWF, which calls on the subject for regional cooperation.
One-century projections show for India a contrasting situation in time and space: in the upper Indus, the flow will increase from 14% to 90% in the first decades, before decreasing in the same proportions of here at 2100. For the Ganges, the upstream part will experience the same type of variation, while in the area further downstream, where the water supply is mainly due to monsoon precipitation, the impact of deglaciation will be practically negligible. .
These differences are due to the fact that glacial meltwater represents only 5% of the flow of Indian rivers, but contributes greatly to their regulation, especially during the dry season. Thus, for the Ganges, the loss of glacial meltwater would reduce the flow by two thirds from July to September, which would imply a water shortage for 500 million people and would affect 37% of Indian irrigated crops, assures the report.
WWF also highlights the increased risks of sudden emptying of glacial lakes. Supercharged due to melting ice, they are indeed more likely to break the natural dikes that contain them. And cause catastrophic flooding below, sometimes for tens of kilometers. Of the 229 glaciers identified in the Arun basin in Tibet, 24 "are potentially dangerous," the report notes.
In China, the Yangzi and Yellow River basins are experiencing a decrease in the surface areas of wetlands and lakes. Desertification is progressing. The Yellow River was unable to reach the sea for 226 days in 1997, a record year.
"All the observations agree", confirms Yves Arnaud (IRD, Grenoble glaciology laboratory). The topographic and satellite data that he himself analyzed show a decrease in the thickness of the Himalayan glaciers varying from 0,2 m to 1 meter for fifty years ...