In the latest among a series of studies on risks of glacial lake outburst floods (GLOFs), and their impact on infrastructure and settlements downstream of such lakes, the Indian Space Research Organisation (ISRO) has released satellite-data-based analysis on expansion of glacial lakes in the catchments of Indian Himalayan river basins.
ISRO’s analysis says of the 2,431 lakes larger than 10 hectares (identified during 2016-17), 676 glacial lakes had expanded significantly since 1984. Of these 676 lakes, 601 lakes had more than doubled in size, 10 lakes had grown between 1.5 to 2 times, and 65 lakes had grown 1.5 times.
India’s ace space research body looked at satellite data archives spanning past four decades to assess changes in the glaciated environment. Long-term satellite imagery covering the catchments of Indian Himalayan river basins — spread over India, Nepal, Tibet, and Bhutan — is available from 1984 onwards, till 2023.
ISRO said 130 of the 676 lakes are situated in India, in the Indus (65), Ganga (7), and Brahmaputra (58) river basins. These lakes have expanded as glaciers are retreating at an ever faster rate due to global warming.
The movement of glaciers causes erosion and creates depressions in the surrounding topography. When they retreat, meltwater starts to accumulate in such depressions, giving birth to glacier lakes.
While glacial lakes are crucial sources of freshwater for rivers, they also pose significant risks, specifically of GLOFs, which can have devastating consequences on communities downstream.
“GLOFs occur when glacial lakes release large volumes of meltwater due to the failure of natural dams… resulting in sudden and severe flooding downstream. These dam failures can be triggered by various factors, including avalanches of ice or rock,” ISRO said.
The monitoring of glacial lakes and their expansion in the Himalayan region is challenging due to the rugged terrain. This is where, according to ISRO, satellite remote-sensing technology “proves to be an excellent tool for… monitoring due its wide coverage and revisit capability”.
“Satellite-derived long-term change analysis provide valuable insights for understanding glacial lake dynamics, which are essential for assessing environmental impacts and developing strategies for GLOM risk management and climate change adaptation in glacial environments,” ISRO said.
Glaciologist Ashim Sattar, Assistant Professor, IIT, Bhubaneswar, said: “Most of the glacial lake sites are not accessible by motorable roads. In this scenario, remote sensing tools, which are highly advanced now, can help us monitor the growth of glacial lakes and understand their dynamics”.
He also said fieldwork can be carried out at lake sites which have been identified as potentially critical. “Fieldwork is crucial to set up instrumentation for early warning systems. These can include installing motion detection cameras, water level sensors, discharge meters etc. that can capture anomalous activity in and around glacial lakes,” Sattar said.
In 2023, a study published in the Journal of Geophysical Research examined the risks posed by Ghepan Gath lake — located at an elevation of 4,068 m in Himachal Pradesh — to Sissu in Lahaul valley, and modelled the impacts of lowering the water levels in the lake.
It found that lowering of the lake levels by 10 to 30 m significantly reduces the impacts on Sissu town, though not completely eliminating the risks posed by a GLOM event.
One way to syphon off lake water is by using long High Density Polyethylene (HDPE) pipes. In 2016, members of the Sikkim State Disaster Management Authority and Sikkim’s Department of Science and Technology and Climate Change, among others, used this method to reduce water levels in Sikkim’s South Lhonak Lake.
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