Sikkim flood was a matter of time despite uncertainties, scientists knew Premium
The Hindu
Glacial lake outburst floods (GLOFs) in the Sikkim Himalaya, caused by melting glaciers, have led to loss of life and property. Climate change has increased the frequency and intensity of extreme weather, while human activities on unstable terrain have worsened the effects. Scientists had anticipated the disaster, and research has identified 12 'critical' and 93 'potentially critical' glacial lakes. Monitoring systems and moderating construction activities are needed to mitigate the risks.
The Teesta basin in the Sikkim Himalaya is home to several glacial lakes in the high-altitude, glacier-covered terrain. Among them, South Lhonak Lake stands out as one of the largest and fastest-growing.
Although these lakes are primarily situated in remote and uninhabited mountain valleys, the consequences of glacial lake outburst floods (GLOFs) can extend over tens of kilometres downstream, resulting in loss of human life and significant damage to property and infrastructure. A GLOF occurs when the weak, unstable natural moraine that holds a glacial lake fails can no longer hold the water in the glacial lake. Events like earthquakes, cloudbursts, and avalanches can trigger a GLOF by breaking the moraine.
A recent cloudburst above South Lhonak Lake caused it to breach its embankment, dumping the water into a channel that caused the water in the Chungthang dam reservoir to overflow as well as the reservoir itself to suffer damage. All this then triggered abrupt and devastating flash floods in different parts of the hilly state of Sikkim.
Meteorologists have stressed that while existing weather conditions were indeed favourable for heavy to extremely heavy rainfall, since a low-pressure atmospheric system was nearby, the flash floods can’t be solely attributed to the singular instance of extreme weather. Climate change has played a big part in altering the frequency and amplifying the intensity of such weather phenomena – and human activities on unstable terrain have made their effects more devastating.
“We all know that in a warming world, the potential for cloudbursts, extreme rains, and GLOF has gone up,” Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology, Pune. “Ocean warming has already increased moisture levels over the region. The low-pressure area near the region further increased the moisture, [providing] a conducive environment for torrential rains.”
As it happens, scientists had anticipated the Sikkim disaster as early as 2021, when, in a study published in the journal Geomorphology, they highlighted the expanding dimensions of the Lhonak glacial lake, which rendered a GLOF more likely due to cloudbursts.
“There has been a substantial increase in the number of glacial lakes as the glaciers are melting due to global warming,” Farooq Azam, a glaciologist at the Indian Institute of Technology, Indore, said. “When the glaciers advance, they erode the river bed, leading to the deepening of the river. Also, climate change has resulted in erratic precipitation, including events like cloudbursts, as we saw in Sikkim, leading to the partial breach of the moraine dam.”