As glaciers melt, flood risks threaten millions

The Shishpar glacier in northern Pakistan started rapidly thawing during a record heat wave last spring. The melted snow and ice flowed into a nearby ice-dammed lake until water levels grew too high, triggering a large flash flood that wiped out a key bridge and battered a downstream village.

This is not a unique event. Across the world’s iciest regions, communities live with the looming threat of inland tsunamis — massive walls of water moving quickly and forcefully from melting glaciers, known as glacial lake outburst floods.

A study published last week in Nature Communications found that around 15 million people live in danger of such glacial flooding. More than half of those at risk are in four countries: India, Pakistan, Peru and China.

“It sounds quite dire, but it doesn’t need to be,” said Tom Robinson, a co-author of the study and risk researcher at the University of Canterbury in New Zealand. “With thoughtful investment and careful planning, we can avoid these (flooding disasters).”

Glacial lake outburst floods have existed for as long as gla- ciers, but the risk has greatly increased in recent decades due to climate change, Robinson said. The floods “pose a globally significant hazard, and that hazard appears to be getting significantly worse with climate change,” he said.

While not all glacial floods are caused by heat waves like the one that triggered the Shishpar flood, climate change is also making extreme heat more common. A study showed that climate change made last year’s record heat in India and Pakistan 30 times more likely to occur and elevated temperatures of the heat wave by about 1.8 degrees Fahren- heit compared to preindustrial times.

Global populations also have skyrocketed, particu- larly downstream of many glacial lakes. In 1942, a gla- cial lake outburst near Huaraz, Peru, killed more than 1,000 people. A breach on that glacial lake today, which many fear, could affect more than 100,000 people living downstream.

Taking into account lake conditions and the number of people within 30 miles down- stream, the study assessed the areas with the highest danger from glacial lake outburst flooding. They also looked at the level of human development, determined by the United Nations, and a corrup- tion index from nonprofit Transparency International for each location, which could influence how resources are allocated in flood prevention and response.

They found that highmountain Asia, home to the Himalayas, ranked the most dangerous, with 9 million people exposed to 2,211 lakes. Pakistan and China had the highest risk globally, with nearly 2 million and 1 million people exposed, respectively.

The High Arctic, such as Greenland, had the lowest danger. Even though Green- land had the highest number of glacial lakes worldwide, very few people live there and are in harm’s way. The Pacific Northwest, particu- larly in Canada, also had a large number of glacial lakes, although the population is not as vulnerable.

The most surprising part of the study came in the Andes, Robinson said. Peru ranked third globally in dan- ger risk. Danger overall in the Andes comes in a close sec- ond behind high-mountain Asia, but the study found the area receives much less attention from the scientific world.

The number of glacial lakes across the Andes increased by 93% over the past two decades, compared to 37% in high-mountain Asia. Yet the researchers found the Hima- layas accounted for 142 studies in English language jour- nals between 1990 and 2015. Fewer than 100 studies on glacial lake outburst flooding in the Andes have been published in similar journals since 1979, the study said.

“The focus over the last few years on high-mountain Asia is good,” Robinson said. “But that shouldn’t come at the expense of other places with really high danger as well.”

Juan Torres, a risk researcher at National Institute for Research on Glaciers and Mountain Ecosystems in Peru, said he and his colleagues have published many Spanish-only studies in four sub-basins in the region and plan to publish more in the upcoming year. He agrees that the area is not well-researched in general and wants more collaboration between his organization and other universities around the world.