Climate change swells Himalayan glacial lakes, raising flood risk: Study

Dehradun: Rapid warming across the Himalaya-Karakoram is not just shrinking glaciers -- it is creating a fast-growing flood hazard. Rising temperatures are accelerating glacier melt, causing hundreds of glacial lakes to expand across the high mountains and increasing the risk of sudden Glacial Lake Outburst Floods (GLOFs) that can devastate downstream communities within hours, a new study by researchers from the Indian Institute of Science, the University of Kashmir and New York University has warned.Published in Nature, the study, ‘Glacial lakes and GLOFs in a warming Himalaya-Karakoram region: current understanding, challenges and the way forward', found that the region is warming "significantly faster than the global average", triggering widespread glacier retreat and the rapid formation and enlargement of unstable ice- and debris-dammed lakes. As glaciers melt, water accumulates in depressions to form glacial lakes. These lakes are often held back by loose rock and ice -- natural dams far less stable than solid bedrock. When such dams fail, massive torrents of water can surge downstream within hours.
According to the research, at least 388 GLOF events have already been documented in the Himalaya-Karakoram region, with the highest numbers recorded in Karakoram, followed by the Central and Eastern Himalayas. The researchers highlighted that most floods originate from moraine- or ice-dammed lakes, typically triggered by ice avalanches, landslides, or extreme rainfall.Satellite data show a steady increase in both the number and area of glacial lakes in recent decades. While figures vary across inventories due to differences in mapping methods, the overall trend, the authors emphasise, is unmistakable: glacial lakes are expanding in both size and number. In some sub-regions, the total glacial lake area has grown by nearly 1% annually, according to the findings.The danger is amplified by rising human exposure. Around 1 million people live within 10 km of a glacial lake in High Mountain Asia. Roads, hydropower projects, bridges and settlements are increasingly being built in fragile mountain valleys, magnifying the potential impact of sudden outbursts, the study said.Despite advances in satellite monitoring, significant knowledge gaps remain. "Many glacial lake inventories use different definitions and size thresholds, making comparisons difficult. Most datasets provide static snapshots and fail to capture rapid changes or seasonal fluctuations. Critical information, such as lake depth, dam stability and downstream vulnerability, is often missing due to limited field access in remote terrain," the authors said. The study found that while temperatures across the Himalaya-Karakoram show a consistent rise, rainfall patterns are more complex. Unlike warming trends, precipitation does not follow a uniform pattern across the region, the researchers noted. They added that local geography, including mountain height, slope orientation and valley systems, strongly influences rainfall and snowfall, leading to sharp differences even between neighbouring areas.Long-term records showed a notable decline in monsoon and annual rainfall in the northwest Indian Himalayas since the late 19th century, and in the western Himalayas since the 1960s. For Uttarakhand, the study highlighted a marked decline in precipitation between 1901 and 2003. Winter snowfall has generally decreased in many western Himalayan areas since the mid-1970s, though trends vary locally. Some pockets, such as parts of the upper Indus basin, saw rising winter precipitation, while the Everest region shows contrasting north-south trends. Overall, while warming is widespread and steady -- particularly since the 1980s -- rainfall trends remain mixed and uncertain. Climate models also showed greater uncertainty in predicting future precipitation than temperature. This combination of rising heat and unpredictable rainfall adds further instability to glaciers, affecting how quickly ice melts and lakes evolve, the research said. To reduce risks, the researchers recommended a mix of structural and non-structural measures. "Structural interventions include controlled drainage, spillways and dam reinforcement to safely lower lake levels, though these projects are costly and technically demanding. Community-based approaches such as early warning systems, evacuation planning, public awareness campaigns and regular drills are equally critical, particularly in developing mountain regions," they said.The authors argued that GLOF risk must be integrated into national development planning, land-use policies and infrastructure design. Cross-border cooperation is also essential, as rivers and glaciers span multiple countries. "The overarching message is clear: as the Himalaya-Karakoram continues to warm, glacial lakes will expand and GLOF hazards will intensify. Managing this growing threat requires coordinated science, policy and community action -- before the next outburst strikes," they added.