Edmund Hillary and Sherpa Tenzing Norgay were trying today to climb Everest, they would save themselves 5 kilometers of ascent on the perilous Khumbu Glacier, which has declined since their 1953 feat. Nicknamed the "water tower of Asia", the Himalayan massif melts its glaciers, under the effect of the warming. The World Wide Fund for Nature (WWF), which has collected 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 of the major rivers of Asia: the Ganges, Indus, Brahmaputra, Salween, Mekong, Yangzi (Blue River) and Huang He (river Yellow). The 8,6 millions of cubic meters that flow each year from the peaks provide freshwater to millions of people. The accelerated melting of glaciers could mean more floods for them in the first few decades, before a shortage ensues.
Hydroelectric power, agriculture, some industries depend directly on freshwater supply: the economic impact will be substantial, worries WWF, which calls for regional cooperation on the subject.
Projections to a century show for India a contrasted 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. here at 2100. For the Ganges, the upstream part will experience the same type of variation, while in the downstream zone, where water supply is mainly due to monsoon rainfall, the impact of deglaciation will be practically negligible.
These differences are due to the fact that glacier meltwater accounts for 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 of two-thirds from July to September, which would imply a shortage of water for 500 million people and affect 37% of Indian irrigated crops, ensures the report.
The 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 Yangtze and Yellow River basins are experiencing a decline in wetland and lake areas. Desertification is progressing. The Yellow River could not reach the sea during 226 days in 1997, 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 ...