About 294,000 people in Nepal live in areas of extreme flood risk, including 108,000 directly downstream of glacial lakes that could release water without warning, according to a study published on Thursday in Scientific Reports.
The analysis was largely finished before August, when a slab of rock and ice fell from Langtang Lirung, a peak close to 24,000 feet, and sent a debris flow roughly 120 miles down the Bhote Koshi river and its tributaries. Nepali authorities report at least 1,455 deaths, 5,285 people still missing, and nearly 14,000 rescued. In some communities the water rose about 330 feet.
Where the exposure is
The team mapped every river originating in Nepal's transboundary basins along the borders with Tibet and India, isolated areas within 50 kilometres downstream of glacial lakes or basin headwaters, and then marked what a 50-metre rise in water would reach.
Most of the danger is not in the mountains but at the bottom of them. "There's a lot of development going on very close to the river channel in these potentially hazardous zones," said Scott Watson of the University of Leeds. Tourism and trade routes pulled construction downhill, and hydropower investment brought paved roads into high catchments.
Building in the wrong place
The study found that the area built within 50 vertical metres of riverbanks increased by about 46 percent between 2016 and 2023. Once a settlement forms, schools and clinics follow, and moving it becomes politically and financially painful.
Upstream, the hazard is growing. As glaciers retreat and permafrost thaws, thousands of glacial lakes are forming, many dammed by ice that can fail suddenly. "The risk could even be higher" than the paper estimates, said Dipesh Chapagain of the United Nations University, who was not involved in the work. The August event, he said, set a new threshold.
What the authors ask for
Their recommendations are unglamorous: land-use zoning that keeps new construction out of the highest-risk corridors, and early-warning systems that work on the timelines these floods actually give communities, which can be minutes.
Nepal is also rebuilding. Researchers argue that recovery spending is the moment to move people and infrastructure away from channels that have now demonstrated what they can do.