Around 15 million people worldwide are at increased risk of flooding due to melting mountain glaciers, according to researchers in a report released on Tuesday. Communities in Asia are most at risk.

Often, runoff from melting glaciers pools in little lakes that are kept back by obstructions like boulders. The danger arises when a lake overflows, breaking through its protective natural barrier and unleashing a flood of water into mountain valleys.

Scientists have assessed for the first time how many people globally are at risk from these floods, finding that more than half of vulnerable populations live in India, Pakistan, China, and Peru.

Danger is highest, they report in a study published in the journal Nature Communications, when a large number of people live near a lake.

“Our work does not just focus on the size or number of glacier lakes – no disaster is natural – it is the presence of people, especially vulnerable people, in the landscape that causes a disaster,” said Stuart Dunning, a physical geographer at Britain’s Newcastle University, and a co-author of the study.

Glacial lake outburst floods are projected to worsen in a warming climate.

Collectively, the world’s glaciers lost about 332 gigatonnes of ice a year between 2006 and 2016. Since 1990, the number and volume of glacial lakes worldwide have each increased by about 50%.

In the high mountains of Asia, some 9 million people live near more than 2,000 glacial lakes. In 2021, more than 100 people were killed in India in an outburst flood in its northern mountains.