Three years ago on this day, Sikkim experienced a devastating Glacial Lake Outburst Flood (GLOF) when a massive landmass slipped into the South Lhonak lake, triggering a flash flood downstream along the Teesta river basin. The GLOF officially claimed 55 lives, left 74 people missing and 7,025 people displaced, according to the National Disaster Management Authority’s “Post Disaster Needs Assessment (PDNA), 2023” report. Overall, the October 4, 2023 GLOF has affected around 80,000 people across 100 villages.
The GLOF also devastated bridges, buildings, agricultural land, roads, and the Teesta III hydropower dam at Chungthang. According to the PDNA report, the total damage and losses amounted to Rs.1,480.066 crore across social, agricultural, tourism and infrastructure sectors.
Three years on, it is pertinent to reiterate the need to better understand GLOF hazards and their impact, and to develop suitable GLOF management policies to mitigate future events.
GLOFs are among the most complex natural disasters occurring in high-altitude regions. When a glacial lake collapses, it starts a chain of events such as landslides, mudslides, flash floods, and flow of debris downstream.
Frequency and intensity of these events is only increasing with time. A December 2025 study, published in the journal Nature Communications, confirms that 609 GLOF events occurred worldwide from 1900 to 2020, causing a total of more than over 13,000 fatalities. The study further shows that, on average, the annual frequency of GLOFs increased from 5.2 events in 1981-90 to 15.2 in 2011-20.
Around 39.6 per cent of the total GLOFs occurred in Southwest, Southeast and Central Asia, followed by the Low Latitudes, or the geographical regions located close to the Earth's equator, specifically between 0° and 30° north or south latitude at 21.7 per cent. Then come the Southern Andes (15.8 per cent), western Canada and the US (8.5 per cent), Central Europe (4.3 per cent) and Svalbard (3.8 per cent).
At the country level, Peru is the most affected by GLOFs, recording 117 events during the period of study, followed by China (112 events) and Chile (74 events).
The study attributes the increasing occurrence and spatial heterogeneity of GLOFs to rising global temperatures, which expand glacial lakes, along with regional topography and human activities such as constructing hydropower plants, roads and dams.
Although the disaster is experienced globally, the Hindu Kush Himalaya (HKH) region, comprising eight countries—Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal, and Pakistan—is a hotspot for GLOFs and their associated impacts.
The HKH region's vulnerability stems from its geography, climate and socioeconomic factors such as high poverty levels, rapid population growth, heavy dependence on agriculture, and inadequate disaster management policies and infrastructure. In particular, the lack of early warning systems for GLOFs leave the region’s 270 million people at risk.
According to a September 2025 preprint, the HKH region contains approximately 9,600 glacial lakes covering about 1,088 sq km, with the highest GLOF risk concentrated along the China-Nepal border.
The preprint, “Glacial Lake Outburst Flood Risks, Response Strategies and Adaptation Gaps in the 2 Hindu Kush Himalaya Region”, which has not been peer-reviewed, documents approximately 333 GLOF events in the HKH region between 1833 and 2024. Similar to the global landscape, GLOF frequency in this region increased significantly after 1950, averaging about seven events per decade. China recorded the most GLOF events (202), followed by Pakistan (149), India (60), Nepal (57), Bhutan (21), and Afghanistan (4). Approximately 70 per cent of GLOF events occurred during the monsoon season.
In terms of fatalities, India experienced the highest number of deaths associated with GLOF events (6,119), followed by Pakistan (1,991), China (617), Nepal (36), Bhutan (20) and Afghanistan (15). India also recorded the highest number of people displaced by GLOFs, followed by Nepal and Pakistan. Furthermore, the reported economic losses amounted to US $ 5.3 billion, from just 13 GLOF events. These figures are likely underestimated, as GLOF-related fatalities, displacement, and economic losses are often underreported.
According to the preprint, India experienced 60 GLOF events between 1833 and 024, which claimed 6,119 lives.
The number of recorded events alone does not provide a complete picture of GLOF risk in India. Assessing the expansion of glacial lakes can help assess the risk in the country. In 2011, the Central Water Commission (CWC) and National Remote Sensing Centre (NRSC) identified about 2,028 lakes and waterbodies draining towards India. CWC also monitored 477 glacial lakes and water bodies with a water-spread area of more than 50 hectares that year.
In contrast, NRSC’s 2023 inventory identified 28,043 glacial lakes larger than 0.25 hectares. Monitoring was expanded in 2025. The Swiss Agency for Development and Cooperation (SDC), for the National Disaster Management Authority, monitored an additional 425 glacial lakes measuring 10-50 hectares, including 40 classified as high priority for GLOF risk. In June 2025, the CWC expanded monitoring to another 1,941 glacial lakes larger than 10 hectares.
By June 2025, CWC was monitoring 2,485 glacial lakes and 358 waterbodies across the Indian Himalayan river basins. The total area covered by these glacial lakes and waterbodies increased from 5,28,329 hectares in 2011 to 5,39,402 hectares in June 2025, a 2.1 per cent increase.
While agencies like CWC and NRSC undertake monitoring at the national level, for the Himalayan states, focus must be on improving warning systems and resilience to imminent GLOF events. After the Sikkim event, the Union government in 2025 approved Rs.150 crore for Arunachal Pradesh, Himachal Pradesh, Sikkim and Uttarakhand to implement the National Glacial Lake Outburst Flood Risk Mitigation Project (NGRMP).
Under this initiative, the government aims to construct GLOF-resilient infrastructure and develop early warning systems; implement mitigation measures such as controlled drainage of high-risk glacial lakes; strengthening or protecting lake boundaries; real-time monitoring using remote sensing; installing automatic weather stations; and strengthening downstream dams; and create awareness programs to reduce the risks associated with GLOF hazards.
Already, the Centre has installed two automatic weather stations in Sikkim under NGRMP. However, translating the sanctioned funds and planned interventions into comprehensive, last-mile monitoring, early-warning and community preparedness systems across high-risk locations will take time. This creates an important interim challenge, as a major GLOF could occur before all planned infrastructure and early-warning mechanisms become fully operational.
Therefore, immediate preparedness measures are also necessary while NGRMP is being wholly implemented. These should include strengthening real-time monitoring and early-warning coverage, improving downstream preparedness and evacuation plans, and enhancing community-level awareness in high-risk areas.
Moreover, governments should identify regulations for GLOF-hazard zones that restrict the construction of hotels, settlements and critical infrastructure, and create community-based disaster preparedness with local communities.
Finally, governments should use advanced technologies such as artificial intelligence and increase spending on research and development related to GLOF hazards. The government should prepare a national GLOF disaster database for Himalayan states, reporting frequency, damage, and fatalities, and collect parameters for reducing GLOF, to help policymakers and academics devise possible policies.
In addition, cooperation between the Centre and states, all the way to the district administrations, is essential for immediate preparedness and interim measures to prevent loss of life to an extent. These steps may prove crucial in saving lives and infrastructure, should another Sikkim-like event occur again.
Views expressed are the authors’ own and don’t necessarily reflect those of Down To Earth