The Teesta dam and the long shadow of climate change

2025, an expert committee constituted by the Ministry of Environment, Forests and Climate Change recommended a proposal to rebuild the Teesta-3 dam on the Teesta river in Sikkim.

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In October 2023, a powerful glacial lake outburst flood (GLOF) from the South Lhonak lake had decimated the dam and its hydroelectric power generation facility. The waters also carried debris from the dam forward like a fluid battering ram, heightening the damage further downstream. In all, over 100 people were killed while more than 80,000 people in four districts were affected. It became clear later that a moraine on the South Lhonak lake's flank suffered a slope failure, weakening the terminus. The failure also sent rocks tumbling into the lake, generating a strong ripple. The outlet subsequently gave way, with satellite data indicating that around 50 billion litres of water had spilled into the valley. The event also set off multiple landslides about 30 to 40 kilometres downstream. Experts who have since been monitoring the lake also said the moraine has remained unstable. The link with global warming

As global warming and particulate matter — especially black carbon, also known as soot — accelerate the melting of Himalayan glaciers, more runoff is pooling into new lakes or adding to the existing ones. The rate of melting is inversely proportional to the volume, so, as glaciers shrink, they melt faster. A report by the Central Water Commission of last year found that the number of “glacial lakes and other water bodies” in the Himalayan region had become 10.8% more numerous between 2011 and 2024 and that their combined surface area had increased by 33.7% in the same period. The South Lhonak lake itself was formed in the early 1960s and grew to 167 hectares by 2023. Glacial retreat has also been known to destabilise extant geological formations and create new sources of risk. Against this background, the expert committee’s decision to recommend the rebuilding of the Teesta-3 dam is worrisome.