New Delhi, Jan 31: The 2023 Sikkim floods were triggered by landslides that were made more likely due to heavy rainfall and were a result of an interplay of climate change, glacier loss and human infrastructure in mountain regions, according to a paper published in the journal Science.
In the paper, an international team of researchers, including those from the Indian Institute of Technology Bhubaneswar, Odisha, have described the sequence of events, including driving factors and causes, that culminated in the massive Sikkim floods.
At least 55 died, 74 left missing and the 1200-megawatt Teesta-III hydropower dam was destroyed.
In October 2023, a multi-hazard cascade in the Sikkim Himalayas was triggered when earth and stones, which had accumulated over time due to land eroded by a moving glacier, collapsed into the South Lhonak Lake, located in the Upper Teesta basin, they said.
Lead author Ashim Sattar, an assistant professor at the Indian Institute of Technology, Bhubaneswar, said glacial lakes are growing in number and size, and thus, need to be critically and urgently evaluated for downstream hazards and damage potential.
“Climate change is leading to changes in permafrost temperatures, increasing the risk of slope failures that can lead to avalanches or trigger glacial lake outburst floods in the high mountains,” Sattar said.
The team described that on October 3 and 4, 2023, the Teesta Valley in West Bengal experienced heavy rainfall, driven by climate change, which saturated the soil and increased the vulnerability of slopes to failure.
“This preconditioning effect primed the landscape, leading to numerous landslides triggered by the GLOF (glacial lake outburst flood) event,” the authors wrote.
A GLOF is a sudden release of water from a glacial lake, which has formed over time due to melting of a glacier.
Further, the landslides so triggered, coupled with rainfall, “intensified the volume and velocity of the floodwaters, leading to more severe impacts on infrastructure, communities and agricultural lands in Sikkim, West Bengal and Bangladesh”.
“A landslide went into a lake and that triggered a wave that eroded a dam at the end of the lake, which resulted in a slurry-like flood for hundreds of kilometres,” said co-author Dan Shugar, a geomorphologist and an associate professor at Canada’s University of Calgary.
The team wrote, “This multihazard cascade exhibits the complex interactions between climate change, glacier mass loss and human infrastructure in mountainous regions.” The findings highlighted the urgency of a “paradigm shift in numerical modelling and observational techniques for GLOFs”.
The urgency extends to improving GLOF risk management and infrastructure development in high mountain regions, the authors said. PTI
