Himalayas face severe glacial flood risks in years ahead, UN official warns

Reutersin an interview. Researchers identified 47 potentially dangerous glacial lakes in Nepal, China and India in 2020. The real number has since been estimated to be significantly higher.

The population at risk "goes into the millions", said Wignaraja, who also serves as regional director for Asia and the Pacific at the United Nations Development Programme (UNDP). She cited updated data compiled by UNDP and partner organisations in June.

Last week's devastating flood in Nepal was triggered when parts of a glacier near the Langtang Lirung mountain peak collapsed and fell to the valley floor, unleashing a landslide that sent a flood wave down the Trishuli River.

Glacier lake outbursts are a somewhat different phenomenon; they happen when melting glacier water builds up behind a natural barrier, with pressure eventually resulting in a break or overflow that sends a flash flood downstream.

Both threats are on the rise, UN officials say, as climate change accelerates glacier melt in the region, loosening rocks and putting more pressure on glacier lake barriers. The region's mountains are also relatively young, Wignaraja said, and thus more liable to tectonic shifts that can also trigger sudden glacier or lake barrier collapses.

Nepal highly dependent on glaciers. Researchers have found potentially dangerous glacial lakes across large parts of the Hindu Kush region. Read More:Nepal flood death toll crosses 1,000, rescuers reach remote areas.

But Wignaraja said no country in the region depends more on glaciers for both water supplies and income than Nepal, which now faces "some very, very hard choices". For many who live along rivers, moving to higher ground may not be financially viable.

Critical infrastructure will also remain vulnerable. Nepal's loss of power production could be more severe than indicated by some assessments. UNDP said the flood had taken out 15 major power stations under construction, in addition to those in operation.

Wignaraja said electrical networks and hydropower stations could be made more resilient to floods with new technology. But last week's "mud and ice tidal wave" would have overcome most of the defences available. "There's no construction that could have ​stopped this," she said.