Friday, January 31, 2025

Drivers, causes and impacts of the 2023 Sikkim flood in India



Summary author: Walter Beckwith


American Association for the Advancement of Science (AAAS)


Concrete dam of the Teesta III hydropower plant completely destroyed by the flood disaster

In a comprehensive analysis, researchers present the divers, 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. South Lhonak Lake – perched at 5200 meters above sea level in the Upper Teesta basin of Sikkim, India – is among the region's largest and most rapidly expanding glacial lakes, posing severe hazards due to its potential for GLOFs. These hazards were realized on October 3, 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 modeling, Ashim Sattar and colleagues present 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-meter tsunami-like wave that breached and eroded the frontal moraine containing the waterbody, releasing roughly half of the lake’s volume (~50 million mof water) and ~270 million m3 of sediment into the Teesta River valley. Moreover, Sikkim 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 kilometers 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.


Earth scientists study Sikkim flood in India to help others prepare for similar disasters



UCalgary scientist says it’s important to determine what happened and what can be learned




University of Calgary

University of Calgary scientist Dan Shugar 

image: 

Dan Shugar, an associate professor with the Department of Earth, Energy and Environment in the Faculty of Science at the University of Calgary, says it’s important to analyse what happened in the Sikkim flood and what can be learned from it as rapid climate warning affects mountain regions around the world.

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Credit: Courtesy: Dan Shugar/University of Calgary




Experts from the global Earth science community – including a scientist from the University of Calgary – have pieced together what happened during the massive Sikkim flood to try to help others prepare for similar disasters.

On Oct. 3, 2023, a multi-hazard cascade in the Sikkim Himalaya, India, was triggered by a permanently frozen (permafrost) lateral moraine – debris from erosion along a glacier – collapsing into South Lhonak Lake.

“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,” explains Dr. Dan Shugar, PhD, an associate professor with the Department of Earth, Energy and Environment in the Faculty of Science.

Known as a glacial lake outburst flood, it killed at least 55 people, left dozens more missing, damaged agricultural land and destroyed a hydropower dam.

The Sikkim flood was declared one of the worst climate-related disasters to have occurred on the continent that year by the World Meteorological Organization’s State of the Climate in Asia 2023 report.

new paper in the prestigious journal, Science, presents a collaborative effort by scientists, academics, government departments, non-governmental organizations and others to investigate the event.

Shugar, a geomorphologist who’s a co-author on the paper, says it’s important to forensically analyse what happened and what can be learned from it as rapid climate warning affects mountain regions around the world.

The paper looks at the drivers and causes and assesses the downstream impacts of the hazard cascade using high-resolution satellite imagery, seismic data, meteorological data and field observations. It also explores the triggers of the flood and reconstructs its hydraulic dynamics, evaluates downstream implications and considers the long-term impacts of the event.

“The assessment indicates that the high hazard level arises not only from the flood itself but also from the subsequent processes it triggers,” says the paper.

Dr. Ashim Sattar, PhD, the study’s lead author who’s an assistant professor in the School of Earth, Ocean and Climate sciences at the Indian Institute of Technology, adds that the Sikkim flood had devastating effects for downstream regions.

“This is high time to be building resilience in downstream regions that are exposed to such potentially catastrophic events in the Himalaya,” he says in a statement.

“The threat of these catastrophic events is growing, urging us to act with urgency in protecting both our environment and communities in the Himalaya and similar regions around the world.”

Sattar says glacial lakes are growing in number and size, so they 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.”

In Canada, for example, a glacial lake outburst flood in British Columbia’s southern Coast Mountains destroyed forest and salmon spawning habitat in November 2020.

Shugar, who has studied both events, says they can have serious implications for people and infrastructure.

“This study (on the Sikkim flood) is a good example of a mountain disaster galvanizing the global Earth science research community to work together on a common goal,” he says.

“Advances in Earth observation technologies over the last decade have dramatically improved our ability to understand these sorts of events, and ultimately, leading to disaster risk reduction.”

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