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2023 Sikkim floods linked to climate change, glacier loss: study

The October 2023 Sikkim floods, caused by a Glacial Lake Outburst Flood (GLOF) at South Lhonak Lake, killed at least 55 and devastated infrastructure. A study confirms the moraine's collapse, worsened by climate change, was the key cause.

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The October 2023 floods in Sikkim left at least 55 dead and many missing, caused by a large rock, ice, and sediment mass collapsing in the South Lhonak glacial lake. This triggered a Glacial Lake Outburst Flood (GLOF), devastating the region, destroying the Teesta-III dam, and damaging infrastructure in Sikkim, West Bengal, and Bangladesh.

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Sikkim floods caused by GLOF

A year-long study published in Science reveals the flood's cause. Researchers from the Indian Institute of Technology Bhubaneswar and an international team investigated the events leading to the disaster. The study found that the moraine's collapse, a mass of frozen glacial debris, caused a massive wave that breached the lake's natural dam. This unleashed 50 million cubic meters of water, equivalent to 20,000 Olympic-sized swimming pools, which rapidly flowed downstream.

The study revealed no evidence of a cloudburst in the area, contradicting the Sikkim government’s previous suggestion. They had reported that a cloudburst could have preceded the GLOF. However, the study confirms the disaster’s primary cause was the moraine’s collapse, not a cloudburst.

The moraine had been shifting for years before the collapse. Between 2016 and 2023, it moved up to 15 meters per year, indicating instability. The thawing of permafrost due to rising temperatures from climate change likely weakened the moraine. The failure of the moraine on October 3, 2023, released a tsunami-like wave that reached the hydropower facilities two hours later.

Flood moved massive sediment, damaging infrastructure

The floodwaters carried massive amounts of sediment, causing erosion and devastation downstream. Approximately 270 million cubic meters of sediment, enough to fill 108,000 Olympic-sized swimming pools, were moved by the flood, severely damaging farms, homes, and infrastructure.

The study emphasises climate change’s role in exacerbating the disaster. Rising temperatures have melted glaciers and thawed permafrost, increasing landslide and GLOF risks. Heavy rainfall, intensified by climate change, saturated the soil, making it more prone to landslides.

Besides natural causes, human infrastructure like hydropower projects near glaciers and glacial lakes has increased the region’s vulnerability. The Teesta-III hydropower dam was destroyed by the flood.

Lead author Ashim Sattar of IIT Bhubaneswar pointed out that as glaciers and glacial lakes grow, they pose an increasing risk to downstream communities. He called for urgent measures to assess and manage the hazards associated with these lakes and to improve early warning systems and disaster preparedness in vulnerable regions.

South Lhonak Lake remains unstable

The South Lhonak Lake, where the GLOF originated, remains at high risk for future outburst floods. Despite the October 2023 event, the lake area shows signs of instability. The study's authors urge authorities to take immediate action to reduce future GLOF risks in the region, including improving early warning systems, enhancing regulatory frameworks, and changing GLOF risk modelling and management.

The study highlights the need for better disaster management strategies and robust infrastructure in high mountain regions to prevent similar disasters. As climate change affects the region, the risk of such catastrophic events is expected to increase, making it essential to adapt and prepare for the future.

The flood in Sikkim in 2023 served as a stark reminder of how vulnerable mountain regions are to the combined effects of climate change, glacial loss, and human infrastructure.

The study provides insights into the disaster’s causes and stresses the urgent need for improved risk management and infrastructure development in the Himalayas. With ongoing climate change impacts, proactive steps are essential to protect communities and ecosystems from future GLOFs and similar hazards.

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