Global climate change is melting Himalayan glaciers at an unprecedented rate, yet field research into this potentially catastrophic trend is lagging behind.
There are 3,250 glaciers in the Nepal Himalaya and 2,315 of them contain glacial lakes that are increasing in size at varying rates. But no one really knows how many of them are in danger of bursting, and without that information, steps can't be taken to drain the lakes or install early-warning systems for villages downstream.
British geologist John Reynolds was involved in the project to siphon water off the Tsho Rolpa glacial lake in the Rolwaling valley a decade ago, but says the inventory of hazardous glacial lakes is outdated. "There has to be a fresh look at the entire issue because we may be running a high magnitude risk," Reynolds says.
As glaciers shrink, the melting ice causes lakes to grow. The lakes can then breach the loose moraine walls, sending huge floods of water, mud and boulders downstream. Scientists call this GLOF (Glacial Lake Outburst Flood) and these have been occurring with increasing regularity in recent years.
A glacial lake burst in Khumbu in 1985 killed at least 20 people, washed away a hydropower station, the trekking trail to Namche and numerous bridges. The town of Pokhara is situated on the debris field of a gigantic 700-year-old flood that was caused by the emptying of a big lake below Annapurna. The worst-case scenario is a major Himalayan earthquake causing several dozen glacial lakes to burst simultaneously.
Aside from catastrophic floods, scientists are now also doing long-term computer simulations of how global warming will affect the flow of Himalayan rivers in this century. All indications are that spring flow in these rivers will increase over the next 40 years, but the time will come when there will be so little snow in the Himalaya that the rivers will run dry in the lean season. This won't just affect the lives of people in the mountains, but also hundreds of millions of people downstream.
Two years ago, the United Nations Environment Program (UNEP) and the Kathmandu-based International Centre for Integrated Mountain Development (ICIMOD) sounded the alarm that 44 glacial lakes in Nepal and Bhutan were in imminent danger of bursting. There has been little followup field research since then.
Trends elsewhere in the world show mountain regions in the tropics are extremely sensitive to climate change. This year, the US-based Earth Policy Institute reported that the equatorial snows on Kilimanjaro could disappear by 2030. It said the Larsen Ice Shelf in the Antarctica has already shrunk by 40 percent. In Greenland, the Jakobshavn Glacier is now thinning four times faster than it was during the last century. In Central Asia's Tien Shan mountains, glaciers have shrunk by 30 percent between 1955 and 1990.
Scientists say this trend is also affecting the Himalaya-Hindu Kush arc, but there has been no systematic research and regular monitoring since the mid-1990s. Even those studies showed disturbing trends. Records with the Department of Hydrology and Meteorology (DoHM) indicate Japanese researchers had found a majority of the glaciers in the Khumbu region had retreated 30-60m between 1970 and 1989. In the Dhaulagiri region, field studies until 1994 displayed the same trend. Nepal's most studied glacier in Tsorong Himal recorded a 10m retreat between 1978 and 1989.
The 2001 UNEP-ICIMOD warning was not based so much on field research as comparisons of satellite imagery. But even that was alarming enough. "We urgently need to update our glaciological data with field studies, otherwise we won't have any warning when disaster strikes," says hydrologist Arun Bhakta Shrestha at the DoHM.
A recent meeting of glaciologists in May in New Delhi analysed data on how the receding snowlines in the Himalaya caused by climate change would affect the flow of water in the Ganga, Brahmaputra and the Indus rivers. Hydrological simulations for various global warming scenarios showed increased snowmelt would swell rivers by as much as 90 percent in the next few decades before they start drying up.
"In some of the rivers, the flow may go down by as much as 90 percent," says glaciologist Syed Iqbal Hosnain of the University of Calicut, who is studying glacier recession in India's Himachal Pradesh. Such predictions are corroborated by a small scale study in the Modi Khola, north of Pokhara. "The field study shows rivers will continue to have abundant water for the next 50-60 years," says hydrologist Mandira Shrestha at ICIMOD. After that, experts fear, the rivers' flows will decrease dramatically as the snows recede.
The risk of such drastic change is higher in the rivers of eastern Nepal because deglaciation is more pronounced there. Bhutan's glaciers, for instance, are receding three times faster than the glaciers in central Nepal because the mountains of the eastern Himalaya are getting more rain and less snow.
Nearly 70 percent of the water in the Ganga is from tributaries that flow down from Nepal, and if Himalayan glaciers dry up, they will cause the Ganga to dry up in the lean season too.
The Tibetan Plateau is a 'water tower' not just for the Ganga-Brahmaputra-Indus systems but also for the Yangtse, Mekong and the rivers of Burma which all have their headwaters in eastern Tibet.
The Institute of Tibetan Plateau Research at the Chinese Academy of Sciences has reported receding glaciers in Tibet and Yunan and warn that two-thirds of the glaciers in China will disappear by 2050 due to global warming, affecting some 300 million people living downstream.
Although evidence is piling up that climate change will have enormous short-term and longterm impacts in the region, scientists say there isn't enough field research to provide empirical proof about the seriousness of the crisis. At the DoHM, scientists want to do some measurements in the Langtang Glacier north of Kathmandu but can't afford the Rs 500,000 that it will cost. Last year, the UN provided Nepal, Bhutan and India with equipment to check the thickness
of glaciers, but the apparatus is rusting at the ICIMOD office in Kathmandu because there is no money to take it.