On Aug. 26, a rock and ice avalanche triggered a huge flood that swept through a steep valley in Nepal, leaving thousands dead and missing. It was an extreme example of a growing problem across the Himalayas. As glaciers melt, glacial lakes expand and mountain permafrost thaws, the risks from floods, landslides and other high-mountain hazards are increasing. At the same time, more people and infrastructure are moving into the valleys where these hazards are most likely to strike.

Our new study shows how quickly this exposure is growing. We focused on Nepal and the catchment areas of rivers that drain into Nepal. In that region, between 2016 and 2023, the built-up areas potentially exposed to flooding increased by 46%. Across the Nepalese Himalayas, we estimate almost 300,000 people live in these flood-prone areas, including more than 100,000 downstream of glacial lakes.

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