Climate-driven melting of snow and ice continues to swell many lakes in the Himalayas, increasing the risk of catastrophic flooding in downstream communities, new data show. Researchers examining 902 lakes across the snowy, mountainous region found that more than half have increased in area since 2011, some by more than 40%. Overall, the area covered by the lakes grew by 11% over the same period, India’s Central Water Commission reports.
The findings highlight the need for “vigorous monitoring” of rapidly changing glacial lakes and water bodies, the researchers write. The lakes are often held in place by unstable ice dams and gravel bars that can fail with little warning, unleashing deadly torrents. Such “outburst floods” have killed thousands of people across the Himalayas over the past decade, and a warming climate has only increased the risks. The report notes that because outburst floods can be difficult to predict, “A close watch on the relative change in water spread area of even smaller lakes has become very crucial.”
The new numbers come from a periodic review of satellite and aircraft data on select water bodies and glacial lakes—which sit directly adjacent to glaciers—larger than 10 hectares in the four Himalayan nations: India, China, Nepal, and Bhutan. Overall, 458 of the 902 lakes and bodies, or 51%, had grown in area between 2011 and September of this year. Most of the rest either shrank or showed no change, although in 41 cases the trend was uncertain. But the total area covered by 825 of the lakes, finding it had grown to nearly 600,000 hectares, a 10.8% increase.
The results echo those from other recent studies. In April, for example, the Indian Space and Research Organisation released a study of 2431 Himalayan lakes larger than 10 hectares. It found that 676, or 28%, had grown in area from 1984 to 2016.
Such data dramatize the growing risks of outburst floods, says Irfan Rashid, a climate scientist at Kashmir University. “The expansion of glacial lakes should ring alarm bells amongst policymakers,” he says. There’s also a need for greater collaboration among the four Himalayan nations, he adds, given that many watersheds cross national borders.
The Indian government has launched an $18 million (150 crore) effort in the Himalayan states of Himachal Pradesh, Uttarakhand, Sikkim, and Arunachal Pradesh to examine the problem and possible solutions. In Sikkim, a research team recently undertook expeditions to assess nine of the 16 most vulnerable glacial lakes. The team is now identifying possible risk mitigation measures, including installing monitoring equipment and water diversion channels, says Sandeep Tambe, secretary to Sikkim’s Department of Science and Technology.
National disaster planning officials have also identified 47 dams in valleys downstream of the lakes that could be threatened by outburst floods. They have completed reports on 31 of those, including assessments of whether their spillways are big enough to handle a flood. A November study estimated that, in the eastern Himalayas, more than 10,000 people living in nearly 2000 settlements, as well as five bridges and two hydropower plants, are at risk from outbreak floods.