What Triggered the Devastating Floods in Nepal and Tibet, and Are We Due for More in the Future? Here’s What Scientists Know So Far
Natural hazards researchers suspect that a landslide involving a glacier triggered the event, and they say more could happen because of human-caused climate change
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On August 26, devastating flash floods washed away buildings, bridges and other infrastructure near the border between Nepal and China-governed Tibet. The natural disaster has killed more than 900 people and left nearly 5,000 missing as of August 31, according to authorities.
“It was a huge gush of mud coming straight towards us,” recalls Keshav Prasad Baral, a 68-year-old survivor, to a team of reporters at the Guardian. “My wife is still somewhere beneath the mud. She’s gone.”
But what caused the catastrophic event, and could more like it happen in the future? Scientists are still putting the pieces together. Here’s what they know so far.
What caused the flooding?
According to the U.S. Geological Survey’s August 27 update, an event in Nepal’s Lāṅṭāṇ National Park in the Himalayas triggered the flooding. The agency says that either a landslide carrying a glacier or a glacier collapse, in which part of it snaps off, may have generated the energy equivalent to a magnitude-5.2 earthquake. Then, debris tumbled downward and triggered the floods.
Many scientists are heavily leaning toward the landslide explanation. The physics of the glacier collapse hypothesis didn’t hold up, according to some natural hazards researchers in a Slack group analyzing the event, reports Science’s Hannah Richter. What’s more, satellite images obtained the evening of August 26 show a bald mountain, hinting at a giant landslide.
“The glacier just came along for the ride,” Göran Ekström, a seismologist at Columbia University, tells the outlet.
However, experts still aren’t sure where all the water came from. At first, scientists thought that a glacial lake had collapsed, but satellite imagery and weather data didn’t suggest any big ones were forming in the region, Ekström tells Mohana Basu at Nature.
It’s more likely that the rush of ice and sediments from the landslide accumulated river water as it barreled downstream, Kristen Cook, a geomorphologist at Grenoble Alpes University in France, tells Science. The USGS says the glacial debris picked up rocky material and water as it sped downhill, generating a debris flow and flood that traveled around 62 miles.
It’s “just a gobsmackingly unbelievable amount of water,” says Daniel Shugar, a geologist at the University of Calgary in Canada, to Laura Paddison, Angela Fritz and Ivana Kottasová at CNN. “Figuring out where that water came from is actually probably the hardest thing about all this.”
Did climate change play a role?
While no attribution study has been done yet, scientists already know that rising global temperatures caused by human activity are destabilizing glaciers in the Himalayas, which contain some of the world’s tallest slopes.
“There’s no question that this event was made more likely because of climate change and that we’re seeing more likely other similar glacier hazards occurring,” says Twila Moon, a glaciologist at the University of Colorado Boulder, to NPR’s Ava Berger, Diaa Hadid and Julia Simon.
Not only are thousands of glaciers losing ice at unprecedented rates; the permafrost they sit atop is also thawing. As that frozen blend of soil, rocks and organic material warms, the mountains and surrounding ice become less stable. In turn, this “can result in massive landslides, triggering a number of cascading processes that can lead to a massive flood and destruction downstream,” Alton Byers, a mountain geographer at the University of Colorado Boulder, tells Nature.
Quick fact: Glacier melt
Last year, researchers reported that even under the most ambitious Paris Agreement goal—keeping the global average temperature no higher than 2.7 degrees Fahrenheit above the pre-industrial level—Earth might lose half of its 200,000 glaciers by 2100.
Scientists say events like this are probably going to become more common as the world continues to heat up. That’s why Shisir Khanal, Nepal’s Minister for Foreign Affairs, called for a “global effort” to address climate change during an August 29 press conference, per the BBC News.
“We request the global community to come together and preserve the Himalayan ecosystem,” he said. The country is one of the world’s lowest contributors of planet-warming greenhouse gases, but it faces some of the worst impacts of climate change.
Shugar echoes that sentiment to PBS News’ Geoff Bennett. “We need to be stepping up to help mitigate these risks and to enhance the resiliency of people living in these environments that are subject to these disasters that, when there’s a climate change link, we in the rich West are largely responsible for,” he says.
What comes next?
Rescue efforts are still underway, and it will likely take weeks to recover all victims. That includes survivors who are stuck atop buildings that rescue teams are struggling to access and hundreds of workers who are trapped in hydropower tunnels.
A monthslong cleanup effort will follow, and some people may never find their loved ones’ bodies, which may have even been swept to India, reports the Guardian’s Hannah Ellis-Petersen.
According to Reuters’ Saurabh Sharma, Nepali officials estimate that it will cost $4 billion to $5 billion, or about a tenth of the country’s economy, to rebuild.
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