As the Himalayas melt, deadly floods become the new normal

For men aged 40 years climate researcherwho grew up in the hills of eastern Nepal and is now studying the dangers of mountains in UN University in Bonn, Germany, the subjects are both professional and deeply personal.

He has watched the risks facing the region change in his lifetime.

“When I was a kid, it wasn’t like that,” he told me. “Or when my parents were little or my grandparents, that wasn’t the biggest challenge [they faced].”

Glaciers collapse, mountains crumble

Then, at 8:37 a.m. Wednesday morning, a mountainside high in the Himalayas collapsed.

The collapse was so large that seismic instruments registered it as a magnitude 5.2 event, and initially thought it was an earthquake. The bedrock beneath the glacier collapsed, carrying large amounts of ice and rock approximately 1,200 meters to the valley floor.

Water, sediment and boulders flow into rivers below, washing away towns and villages along one of Nepal’s most important trade routes with China. At one monitoring station, water rose as high as nine meters in half an hour.

As of Friday, more than 500 people were reported dead in Nepal and Tibet and more than 1,500 people remained missing, including hundreds of foreign nationals.

Dr. Dr. Chapagain is safe. However, the news had a bad impact on him.

“It’s always difficult to convey these bad messages from home,” he said. “It’s becoming more frequent and more intense.”

This disaster is a brutal illustration of the climate problem that scientists have been warning about for years. The frozen architecture of the Himalayas is changing, exposing millions of people to dangers that are increasingly difficult to predict and, in some cases, even more devastating.

How mountains collapse into deadly floods

Experts are still piecing together the chain of events that led to Wednesday’s disaster. Analysis of satellite imagery shows that the bedrock beneath the glacier has collapsed, sending large amounts of ice and rock into the Lhende Khola, a tributary of the Bhotekoshi River, and triggering the destructive flow that followed.

The mechanism is different from the floods caused by glacial lake explosions that Dr. Chapagain and his colleagues at the Global Mountain Safeguard Research program, known as GLOMOlearn to traverse the Hindu Kush Himalayas. GLOMOS is part of UNU Institute for Environment and Human Security.

Theirs latest research analyzed 493 floods from the earliest available records through 2024. It found that these events have become about five times more frequent since 1950, increasing from an average of about seven times per decade to 34 times.

Such floods usually occur when melt water collects in lakes around retreating glaciers, often held back by unstable ice or loose rock and sediment. When these natural dams are broken, large amounts of water can be released in an instant.

Wednesday’s disaster appears to follow a different chain of events.

“This time, an intermediate step was skipped,” says Dr. Chapagain.

Instead of the glacial lake exploding, rock and ice tumbled down the mountainside, producing a torrent beneath it. Researchers are investigating whether the debris temporarily dammed the river before the barrier was removed, an event that Dr. Chapagain has not yet been confirmed.

For scientists, the distinction is important. Downstream, the impacts can be very similar: huge amounts of water, ice and debris are simply released without warning into narrow, inhabited valleys.

It was unclear whether climate change caused Wednesday’s collapse. But global warming is rapidly changing the highland environment where the disaster occurred. As glaciers melt and ice sheets melt, rocks once supported or bound by the ice can become unstable, while increased meltwater can further weaken mountain slopes.

The impact goes far beyond the mountain villages. The Hindu Kush Himalaya drains 10 major river basins where some 2.1 billion people depend for water, food, energy and livelihoods.

When people move in a dangerous direction

But the mountains are not the only thing that has changed. Likewise with the geography of human life beneath it.

When Dr. While Chapagain is small, he said, many families in Nepal’s hilly areas have traditionally built their homes higher on the slopes while growing rice and other crops on flat land close to rivers. The garden of his family’s house is at the top of the mountain. The rice fields are located below, near the river.

Over time, road, business, hotel, and hydroelectric projects became increasingly concentrated in river valleys, where development was easier and economic opportunities were greater. Water sources in some higher-altitude settlements have also dried up, said Dr. Chapagain, thus encouraging people to move to lower ground.

This has created a dangerous convergence: as warming changes the mountains above, more people and infrastructure are congregating in corridors through which water and debris flow.

The valley devastated by flooding on Wednesday was an embodiment of that collision. The Bhote Koshi-Trishuli corridor is the main trade route to Kathmandu and is lined with hydroelectric power stations, bridges, roads, hotels and residential areas. The flood damaged electricity facilities and cut off transportation and communication networks throughout the region.

The danger is obvious. A glacial lake burst hit the same river system last year, killing nine people and leaving 24 missing.

When the minutes matter

For Dr. Chapagain, Wednesday’s disaster also exposed critical weaknesses. How little warning the people received before the disaster that occurred in the mountains befell them.

Nepalese authorities, he said, only became aware of the flooding when they approached the border. Alerts are then channeled downstream via text messages, social media, phone calls, and alarms.

Reducing the danger, he says, starts at a higher level: continuous monitoring of glaciers and unstable slopes, satellite observations, weather and river gauges, and an early warning system capable of giving people enough time to evacuate. Because rivers and glaciers cross national borders, China, Nepal and countries further downstream must also exchange data quickly.

There is a deeper problem. Even if greenhouse gas emissions fall sharply, says Dr. Chapagain, glaciers will continue to lose mass for decades as warming is built into the climate system. How much is lost is ultimately still within humanity’s control. However, what happens in the short term is not the case.

This makes adaptation, in his view, no longer preparation for the distant future.

For communities beneath the Himalayas, that future arrived on Wednesday.