15 million people live in a possible flood path due to melting glaciers

Glacial lakes could cause flooding if an ice or rock dam holding back the water fails, putting about 15 million people at risk, the analysis found.

According to the first global hazard analysis, up to 15 million people live in areas that could be flooded by a natural glacial lake dam failure.

Tom Robinson of the University of Canterbury in New Zealand and colleagues have identified glacial lakes in satellite imagery. They then determined the number of people living within 50 kilometers of each lake and within 1 kilometer of a river where water would flow in the event of a glacial lake outburst (GLOF). These floods can occur when an ice or rock dam holding back a glacial lake fails, or a landslide causes water to slosh over a natural dam.

The researchers found that up to 15 million people could be affected, with 9 million in the Himalayas, 2.5 million in the Andes and 2.2 million in the Alps. More than half of the 15 million live in India, Pakistan, Peru or China.

Flash floods are unlikely in many glacial lakes, says Simon Allen of the University of Zurich in Switzerland, and the study provides a simplistic view of areas that could be affected by any flood, but he says the global view helps draw attention to vulnerable and understudied regions.

In Pakistan, for example, 2.1 million people live in areas of potential risk, but the lakes there are less explored than those in neighboring Nepal, where the government has built expensive spillways on the most dangerous lakes and installed early warning systems. In some cases, a flood wave from a breakthrough may arrive in less than an hour without prior warning.

Lakes in Peru and elsewhere in the Andes, where thousands have died in glacial lake floods since the 1950s, have also been neglected, Robinson said.

Glacial lakes are growing rapidly in number and size as climate change melts more ice, but the frequency of glacial flooding has declined since the 1970s, says Stephan Harrison of the University of Exeter in the UK. As with the warming after the Little Ice Age of the 19th century, it could take several decades between warming and the growth of lakes, he said.