New research into the causes and impacts of the 2023 Sikkim flood in India has been published in the prestigious journal, Science.
Professor Dave Petley, Vice-Chancellor at the University of Hull and a world leader in the study and management of landslides, was part of the international consortium of scientists who undertook a comprehensive analysis, and have presented the drivers, causes, and impacts of the catastrophic 2023 Sikkim glacial lake outburst flood (GLOF).
The findings stress the urgent need to enhance GLOF hazard assessments and improve prediction and early warning systems as melting glaciers steadily raise the risk of GLOFs in the Himalayan region.
Professor Petley said: “This research highlights the need for early warning systems; for mechanisms of risk management and mitigation; for research; and for evaluation of the risks to the growing number of hydropower schemes in this area. There is an urgency to this work, but of course many developing countries are facing reductions in aid.
“Understanding precisely what happened is a key to understanding future risks – and to ensuring that communities are better protected.”
South Lhonak Lake – the source of the 2023 flood – is perched at 5200 metres above sea level in the Upper Teesta basin of Sikkim, India. It is among the region's largest and most rapidly expanding glacial lakes, posing severe hazards due to its potential for GLOFs.
These hazards were realised on 3 and 4 October 2023, when the glacial lake experienced a catastrophic outburst, unleashing a flood cascade that claimed 55 lives, left 74 missing, and caused widespread downstream devastation, including the destruction of the Teesta-III hydropower dam.
Combining high-resolution satellite imagery, seismic and meteorological data, field observations, and numerical modelling, Dr Ashim Sattar, Assistant Professor in the School of Earth, Ocean and Climate Sciences at the Indian Institute of Technology Bhubaneswar in Odisha, India, and fellow scientists around the world have presented a comprehensive and multidisciplinary analysis of the event.
According to the findings, the outburst was triggered when a landslide containing 14.7 million cubic meters (m3) of frozen sediment collapsed into the lake, generating a ~20-metre tsunami-like wave that breached and eroded the frontal moraine containing the waterbody, releasing roughly half of the lake’s volume (~50 million cubic metres of water) and ~270 million cubic metres of sediment into the Teesta River valley.
Moreover, Dr Sattar et al. show that climate warming intensified the event, as heavy rainfall primed the landscape for landslides that compounded sediment transport and downstream destruction in the Teesta Valley, which impacted Sikkim, West Bengal, and Bangladesh and damaged infrastructure as far as 385 kilometres away from the flood’s origin.
According to the authors, the findings underscore the inadequacy of current GLOF models, which often fail to account for erosion, sediment transport, and cascading processes, and highlight the need for enhanced early warning systems, policy reforms, and adaptive risk management strategies, particularly in remote, high-altitude, vulnerable glacial regions like the Himalayas.
Science is published by the American Association for the Advancement of Science (AAAS).
Read Professor Petley’s blog about research into the 2023 Sikkim flood in India here.