Photograph by Enrique Lopez-Tapia, Minden Pictures
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Prayer flags cross Changri Shar Glacier in Sagarmatha National Park in the Himalaya in Nepal. The region is rapidly warming and ice is melting, which can be dangerous.

Photograph by Enrique Lopez-Tapia, Minden Pictures

Flash floods threaten more people than thought, as ice melts

With climate change, ice holding back glacial lakes is melting faster in the Himalayan Tibetan Plateau, threatening downstream communities.

This article was created in partnership with the National Geographic Society.

The Himalaya, the breathtaking consequence of the battle between two tectonic plates, is home to spectacular mountains and a family of glaciers whose waters sustain 1.65 billion people across the region. The thawing of these glaciers leaves behind a myriad of lakes, some of which can suddenly burst their banks and flood downstream.

Plenty of these lakes can also be found in the Tibetan Plateau, an elevated region containing Tibet and parts of western China, and a team of researchers wanted to know if any of them posed a threat to those that live nearby. Their satellite-based assessment of 1,291 glacial lakes in the Tibetan Plateau and along the main Himalaya range found that 16 percent of them potentially threaten human settlements.

All these lakes form naturally, and localized topographical, geological, and hydrological conditions determine which lakes can or will eventually overflow. Anthropogenic climate change, however, is becoming an increasingly antagonizing presence.

“Temperatures are rising, we’re seeing these lakes growing, and the smaller ponds are starting to coalesce,” says Ulyana Horodyskyj, a visiting assistant professor of environmental science at Colorado College and National Geographic Explorer not involved in the work. “This problem is only going to get worse.”

When the levee breaks

Glacial lakes form when glaciers thaw, their waters hemmed in by rocky barriers left over by ancient glaciers that once carved out the landscape. Ice dams can also form a barrier. If something causes the water level to suddenly rise, such as an avalanche of ice or rock, or those barriers break—via an earthquake, say, or prolonged weathering—you can get a glacial lake outburst flood, or GLOF.

These have happened all around the world, and since 1935, around 40 GLOF disasters have taken place across the Tibetan Plateau. Wanting to know what the contemporary danger to human populations were in the area, researchers mixed satellite work with Open Street Map, an open-access, street-level cartography database, to find out.

The size of lake, the size of watershed, the slope of the dam, and the potential for ice avalanches to hit those lakes were all taken into account, as were the number of buildings in the way of the worst-case scenario floods.

As reported in the journal Science Bulletin this week, 210 glacial lakes in the region potentially threaten human settlements. Simon Allen, a glaciologist at the University of Zurich and lead author of the new study, says that he was surprised that the number of potentially hazardous lakes was so high, despite the region being sparsely populated.

Cirenmaco came out as the most dangerous lake. It had already been the source of three major documented GLOF events in the recent past, including one in July 1981 that killed 200 people. Presented the research earlier this month at the annual gathering of the European Geosciences Union in Vienna, Allen told reporters that his team identified a hotspot of high danger on the Chinese-Nepalese border, demonstrating that a single flood can devastate communities in multiple countries at once.

The researchers are already calling for the same remote sensing work to be carried out across much of the wider region, where many more hazardous lakes lie in wait.

Turning back the tide

Sergiu Jiduc, an environmental geoscientist and research consultant for the World Energy Council, emphasizes that ground-based research will always play a vital role in identifying glacial lake hazards. This certainly applies when local communities are involved: their long histories of residing in and living with their surroundings may, among other things, capture environmental changes that might not be detected through remote sensing, says Jiduc, who is also a National Geographic Explorer.

Horodyskyj, who has worked extensively in the region, agrees, while adding that an advantage of remote sensing is that it can catalogue lake hazards over a huge area far more quickly. “This kind of satellite-based approach is basically tailormade for some of the region’s conflict zones,” says Allen.

It’s not just about identifying hazards. This research is designed to help prioritize where mitigation resources are sent. That matters, because danger reduction plans are at present somewhat limited.

Related: Why does this ice bridge keep collapsing?

Joseph Shea, an assistant professor of environmental geomatics at the University of Northern British Columbia, explains that the Nepalese armed forces, among others, sometimes artificially drain lakes—“not an easy undertaking in the slightest,” he adds.

Early warning systems, similar to those that aim to warn populations of volcanic mudslides, can help too, explains Shea, but false alarms and making sure they can run continuously can prove challenging. At the same time, GLOFs can happen so quickly that people might not have much time to get out of harm’s way. You could even set up cheap webcams and add water gauges to the lakes to keep an eye on things, says Horodyskyj, so long as the valleys have a decent WiFi network.

Jiduc, who was also recently funded by the National Geographic Society to head to Pakistan’s Karakoram mountain range to help communities adapt to GLOFs, explains that even if places have an autonomous, effective early warning system in place, it doesn’t solve the problem.

“It’s just buying some time,” he says.

Mercury rising

A recent comprehensive report on the Hindu Kush Himalaya region found that our rapidly warming world is decimating its glaciers. “Irrespective of whether we manage to curb greenhouse gases in line with the Paris agreement, we will lose a third of these glaciers,” says Jiduc. “If not, we could lose up to two-thirds of them.”

Sudeep Thakuri, an associate professor and glaciologist at Tribhuvan University in Kathmandu, says that thanks to this general pattern of glacial shrinkage, glacial lakes are growing rapidly in number and size. Accumulating evidence suggests the potential threats these lakes pose is increasing too.

The calculus is relatively straightforward. Larger lakes lead to larger GLOFs, Allen explains, and the increasing population of lakes higher upslope means that ice avalanches can hit them more easily. As time goes on, GLOFs should increase in frequency and magnitude.

Adam Emmer, an environmental scientist at the Global Change Research Institute of the Czech Academy of Sciences, says that researchers are still trying to pin down the change in GLOF daner over time. It’s fair to say, though, that “the formation and evolution of lakes, as well as some of the GLOF causes, are tied with climate change-driven glacier retreat.”

The clock, therefore, is ticking. If disasters are to be averted, everyone—from policymakers and researchers to charities and communities—has to work closely together. “Transboundary issues require transboundary partnerships,” says Jiduc.