The Teesta. File
| Photo Credit: The Hindu
On January 27, 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. 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.
As The Hindu has reported, the committee’s decision was motivated by the fact that Teesta-3 was “successful” and “commercially viable” and that its power-generating equipment “was largely intact” following the GLOF. Environmental activists and hydrogeology experts alike have expressed misgivings about large hydroelectric power projects in the Himalaya and have questioned the new design’s green clearance. Teesta-3 has also been the subject of several public interest litigations asking for it be scrapped: because of its location (in an earthquake- and landslide-prone area); issues in its techno-economic clearance; its non-compliance with a 1996 notification to have Sikkim hold 51% equity; and alleged corruption.
According to the committee, Teesta-3 2.0 is to be built with concrete alone rather than concrete and rocks as before; to have a spillway nearly three-times more voluminous; and to have an early-warning system for flooding. The facility’s new design is reportedly based on a “worst-case scenario” modelled by the India Meteorological Department, with the “maximum possible rain” in the next century in the region.
But one of the hallmarks of climate change is that it is a risk-multiplier. If the slope failure off the South Lhonak lake had occurred without there being a lake, there is unlikely to have been a flood. Likewise, if the moraine had not collapsed, the gradual accumulation of water may have caused the overtopping to flow into the valley less violently than during a GLOF.
The views of experts
The proliferation of glacial lakes, geological instability, dynamics of transient landscape features, and even the flux of atmospheric soot blowing in from industrial centres in the Gangetic plains all increase risks in a way that cannot reasonably be captured by a rainfall-centric model, however. Experts had already doubted whether the 2023 GLOF was triggered by heavy rain because local weather stations recorded only moderate rainfall or less in the area around the time. Professor Raghu Murtugudde has also written in The Hindu (“The value of attributing extreme events to climate change | Explained”, May 24, 2024) that the relationships between climate change and local rainfall are hard to characterise because the data for modelling is seldom sufficient. In his words, climate models are “notoriously bad at properly capturing normal rainfall and worse at extreme ones”.
On January 30, 2025, an international team including experts from the Indian Institute of Technology Bhubaneswar, the Indian Institute of Science Bengaluru, the Indo Tibetan Border Police, and the Government of Sikkim published a comprehensive assessment of the GLOF (“The Sikkim flood of October 2023: Drivers, causes and impacts of a multihazard cascade”). Among other things, they wrote: “Prevailing GLOF modeling and assessment approaches insufficiently account for processes of erosion and sediment transport, as well as hillslope-channel interactions such as riverbank collapses and landslides triggered by toe-undercutting as well as the impact of sediment transport on local bed elevations and hence water levels. The latter is of particular importance in large river basins because water waves move faster than sediment waves…”.
The commercial viability of Teesta-3, pre-GLOF, speaks to India’s soaring power demand and the pressing need to produce it somewhere. But since climate change multiplies risk everywhere, production in specific locales should be weighed against the consequences. Property and livelihoods downstream of Teesta-3 1.0 suffered greater damage due to the dam being in the swelling river’s way. If the new design holds, Teesta-3 2.0 may be able to reduce the downstream damage due to a (hypothetically) identical flood. But if a stronger and/or significantly different flood occurs, the damage could be even greater. A new facility with more moving parts will also create both new success and failure modes.
The people form the larger picture
The social security of the region’s residents will have to be improved accordingly so that, in the event of a disaster, they are able to piece their lives back together without slipping on any social, health, and/or economic indicators. Brian Stone, Jr., a professor in the School of City and Regional Planning at the Georgia Institute of Technology, U.S., wrote in a 2024 article (“The lunacy of rebuilding in disaster-prone areas”), “We cannot engineer our way out of climate change; retreat is inevitable.” That is, if the climate-change-induced risk to X in an area is to be kept constant, in time either the area will shrink or the costs of maintaining X will increase. X could be property, livelihoods, even human lives.
That the facility was commercially viable is an insufficient excuse to restore it. Instead, the decision should be made within a framework of priorities led by the need to minimise risk to locals, their property, and their livelihoods and maximise their socio-economic resilience. The framework should also include a risk determination matrix with a response plan and a hard ‘unacceptable risk’ level. The cost of these measures should be included in the dam’s hydroelectric power tariff rather than externalising it in the determination of commercial viability. Anything else would be unsustainable by definition.
mukunth.v@thehindu.co.in
Published – February 15, 2025 12:16 am IST
