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Flash flood in Nepal: Researchers are now investigating the role of climate change
Experts still do not understand why such enormous volumes of water appeared in such a short time.
At least 1,455 people have been confirmed dead following the flood disaster in Nepal on 26 August. Over 5,000 are missing.
14 power stations and 38 schools have been completely or partially destroyed.
68 bridges and 42 kilometres of roads were washed away.
Staggering scale
“The scale of the tragedy is immense and overwhelming. This is likely the greatest disaster we have seen in the Himalayas in decades. The videos we have seen show that this is a type of event that is extremely difficult to predict or issue warnings for,” says Pascal Emanuel Egli.
He is a glaciologist and associate professor at NTNU. Egli is an expert in geophysics and glacier hydrology.
These are two fields that together map the Earth's subsurface water resources.
Egli researches natural hazards and water resources related to permafrost, snowmelt, and glaciers.
Researcher friend lost his entire village
Egli monitored the disaster in Nepal closely after the tragedy.
Updates from international research colleagues arrived in his inbox several times an hour.
These included analyses, seismic data, new satellite photos, and aerial and drone imagery. He also received data logs from whatever monitoring equipment remains along the riverbed.
Egli has conducted fieldwork in the region on several occasions. He has also visited the area in Nepal that has been hardest hit.
He explains that a friend and fellow researcher, who currently works abroad, is from a village that has been completely wiped out by the mudflow.
By the time the warning came, many were already dead
On Wednesday 26 August, at 08:37, the disaster began at an altitude of over 5,000 metres in the Rasuwa region.
The region lies along the border between Nepal and Chinese-controlled Tibet.
According to Egli, the disaster was likely triggered when the mountain slope next to the glacier collapsed, taking part of the glacier with it.
A massive block of the glacier's front collapsed and fell hundreds of metres straight down. The debris then continued at tremendous speed into the Trishuli River.
The flash flood raced 20 kilometres down the river course in the first 7 minutes.
"The warning from the authorities arrived at 9am, 23 minutes after the glacier collapse. Approximately 623,000 people received an SMS alert about the approaching disaster. By then, it was far too late for many of them. The warning only reached people living furthest downstream,” says Egli.
What role did the glacier play?
The massive landslide was initially registered as an earthquake. Between 100 million and 250 million cubic metres of rock, ice, and soil were set in motion.
Together, they formed a wall of debris that, at its fastest, travelled at speeds approaching 170–190 kilometres per hour, smashing everything in its path.
“Experts are currently debating what actually triggered the disaster. The landslide itself was massive. Geological factors may be to blame. But the question also remains as to what role the glacier played,” says the NTNU researcher.
Egli has conducted fieldwork on alpine glaciers in Norway, Switzerland, Chile, Pakistan, India, and Nepal.
He currently leads a project in which researchers from 9 countries and 20 research institutions are investigating the impact of climate change on snow and retreating glaciers.
They are also mapping the natural hazards that can arise as a result.
Mountain lost its structural support
Egli explains that the Himalayan glacier in question has been retreating for years due to climate change.
Part of the mountainside had been supported by the glacier for thousands of years. As the glacier melts, the mountain also loses that support.
“In addition, large quantities of meltwater may have exacerbated the instability already present in the mountain,” the researcher says.
The third factor is permafrost, which acts much like a glue holding the rock mass together. As temperatures rise, the permafrost also degrades. This can also make the mountain less stable, Egli explains.
Maps and satellite images of the area show that the landslide originated at an altitude of over 5,000 metres. It cascaded down to 3,800 metres and continued towards the Lhende River.
An area of nearly 2.3 square kilometres collapsed.
How much did climate change contribute?
Drawing on field studies from Norway and Switzerland, Egli’s research group aims to contribute more knowledge about water flow from melting glaciers and glacial lake outburst floods.
The latter originate from lakes formed by glacial ice, meltwater, and precipitation.
Glacial lakes can drain in a matter of hours, and these outbursts can cause extensive damage as they surge downstream.
It was not an outburst flood that caused this disaster, contrary to what many people have assumed.
Egli notes that some researchers believe what happened had less to do with climate influences and more to do with purely geological instability.
“Others, perhaps the majority, believe the timing and massive scale suggest that multiple mechanisms were at play simultaneously. There appears to be a broad consensus that melting and warming have accelerated, destabilising the mountain massif surrounding the glacier,” he says.
The challenge of early warning
Egli is also in the early stages of a project with Swiss and Indian colleagues. The project will take place in Ladakh, India.
The aim is to develop an affordable system for monitoring natural hazards and providing early warnings.
“The early warning technology itself often works well. However, the risk of failure increases if the scale of an event is massive. Training the local population on how the systems operate can also be a challenge,” he says.
In a situation report last updated on 31 August, researchers at Nepalese universities and research institutions raise critical questions:
'Why did we fail to foresee the risk? Why did our warning system not work? Why were the consequences for lives, livelihoods, and infrastructure so severe? And, most importantly: What could we have done differently to reduce such losses?'
Egli refers to a research forum he is part of, where discussions indicate that the authorities have some warning and monitoring measures in place, but that many aspects of the system are failing.
A memo seen states that 'the system is collapsing in several ways.'
Standard SMS alerts about floods and high water levels are sent out, but they lack specific advice about what people should do. Responsibility is unevenly distributed among local, regional, and national authorities.
Low trust in researchers and authorities
Furthermore, people in local communities have little trust in either researchers or the authorities.
Many openly admit to having ignored warnings in the past. Some only take action when they see for themselves that 'something’s happening in the river,' or when a warning comes from someone they trust in the village.
Many initiatives intended to improve the situation come to a halt once external funding runs out. Training and technical maintenance are not sustained.
This region of the Himalayas alone has thousands of glaciers and glacial lakes. What lies ahead as the planet grows warmer?
“The number of glacial lakes has increased as glaciers retreat. This is dangerous, but fortunately we know a lot about their locations. Almost all of them have been mapped. What we know less about, and need to investigate more, is the stability of the moraines damming these lakes,” says Egli.
He explains that there is still a lot we do not know, such as how much permafrost the moraine contains.
As a result, we do not know whether, or when, they might collapse. We also know relatively little about lakes beneath glaciers, or about unstable mountainsides and moraines that could trigger landslides.
Where did all the water come from?
The flash flood in the Himalayas carried between 100 million and 250 million cubic metres of rock and ice.
According to Egli, one of the mysteries is why such enormous volumes of water were released in such a short time.
Why did the water not slow down when the terrain flattened out after approximately seven kilometres, but instead continue with almost the same tremendous force and speed?
He speculates aloud. Perhaps part of the explanation lies in the significant drop in elevation and the fact that the meltwater originated not only from beneath the glacier but also partly from within the mountain itself.
On its way down, the mass of rock and ice struck remnants of another glacier and may have melted them.
“But that's just a hypothesis. We still have a lot to figure out,” says the researcher.
References:
Irarrazaval et al. Shifts in glacier dynamics during land-to-lake terminus transition in western Patagonia, Journal of Glaciology, 2026. DOI: 10.1017/jog.2026.10144
Twinomuhangi et al. Analysis of stationary and non-stationary hydrological extremes under a changing environment: A systematic review, HydroResearch, 2025. DOI: 10.1016/j.hydres.2024.12.007
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Read the Norwegian version of this article on forskning.no
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