KATHMANDU, Nepal—When a flood came roaring down from the mountains last year, Nepali engineer Santosh Adhikari narrowly escaped by scrambling to higher ground. Two weeks ago, another surge barreled down—this one bigger and faster, an unstoppable torrent of water, ice, rock, mud and horror.
The wave tore through the Rasuwagadhi hydropower plant where Adhikari served as the manager, ripping up steel and concrete defenses with explosive force and pouring into the project’s cavernous tunnels. Within seconds, it swallowed the cluster of buildings where the 34-year-old lived. Nothing remained except dark-gray sludge.
Rasuwagadhi was the first of nearly a dozen such installations—some active, others under construction—wrecked by the Aug. 26 disaster in Nepal. The roiling mass of water, unleashed by a glacial collapse, swept down the Trishuli river, devastating a roughly 40-mile corridor of dams that were supposed to drive economic growth for mountainous Nepal. Around 1,400 people have died overall and more than 5,000 are missing.
The tourism- and aid-dependent Himalayan nation, crisscrossed by snowfed rivers, has looked to hydropower as the answer to its energy needs and central to its development plans. Private investment has poured in, quadrupling installed capacity over the past decade. More than 210 projects currently under construction would expand that by 150%, according to industry estimates. The once chronically energy-starved country has even been exporting power in recent years.
The future of that strategy has come into question as a warming planet destabilizes Himalayan glaciers and river systems, increasingly putting human lives and billions of dollars at risk.
Last year’s flood began when water abruptly poured out of a glacial lake 20 miles upstream from Nepal’s border with China. The recent surge, at first thought to be the same, was something even more formidable.
It was sparked by the partial collapse of a glacier and some of its bedrock. That released an avalanche of ice and rock, initially triggering an earthquake report from the U.S. Geological Survey. After plummeting around 4,000 feet, the ice turned into a debris-laden flood that flowed into the Lhende Khola, a river coming down from Tibet, and later joined with the Trishuli river.
The deluge took the same path where power plants are concentrated. “That’s geography and opportunity, not negligence,” said Umesh Haritashya, a professor of geosciences and sustainability at the University of Dayton in Ohio, who is among the scientists studying the causes of the flood. “What’s changed is that the mountain is increasingly unstable, and the hazard is now much bigger, and reaches farther than the assumptions some of these projects were designed against.”
More than 2,000 hydropower workers were scattered across dams, riverside camps, underground power houses and miles-long tunnels when the flood hit. Rescue teams are racing to clear out the tunnels, choked with hardened mud and rock.
Rasuwagadhi’s acting chief executive, Pushkar Amatya, deployed crews and equipment in a last-ditch search for people who might be trapped in the facility’s transformer cavern, but found no one there. He is also searching for his own brother.
Amatya’s 31-year-old brother, Prabin, was an engineer at a hydropower plant under construction downstream. Amatya last heard from him in a text message the morning of the flood, asking if Rasuwagadhi was hit. He later learned from a friend of Prabin’s that the two had fled the surge together.
While the friend ran straight up the mountain, Prabin dashed diagonally across, putting him in the flood’s path.
Chaos of the cryosphere
River-straddling hydropower projects are built to handle monsoon floods, even heavy ones, but high-velocity debris flows are a different beast entirely.
The now-shattered Langtang Khola Hydro project was engineered to withstand a 100-year flood—which has only a 1% chance of occurring in any year and would raise the river level by around 20 feet at its narrow gorge, its managing director said. The recent flood swelled to 20 times that level.
A statistical approach, basing projections on how things have happened in the past, doesn’t work with climate change, said Pierre Biedermann, an environmental consultant for renewable energy projects.
When you have a rain-induced flood, you can calculate the likelihood of it happening again, he said. “But when you get a mountain collapse with a glacier and this kind of cataclysm, you cannot assign a likelihood to it,” Biedermann said.
The August flood was of a type that’s even more rare than glacial lake outburst floods, or GLOFs, and unlikely to be examined in risk assessments for existing projects.
“From my experience—I’ve looked at many of those reports—GLOFs are usually considered, but only to some degree,” said Wolfgang Schwanghart, a professor of geomorphology at Berlin’s Freie University. “The kinds of events that we have seen recently, I haven’t seen them being mentioned anywhere.”
At least a handful of them have taken place in the past five years. In 2021, an ice-and-rock avalanche in northern India killed more than 200 people and destroyed one hydropower project while severely damaging another. Last year, a partial glacier collapse wiped out the Swiss Alps village of Blatten. About 20 million metric tons of ice and rock traveled at a speed of over 120 miles an hour, according to an article published in the journal Nature.
Preliminary calculations based on the seismic signal the landslide produced indicate that the ice-and-rock avalanche in Nepal was likely 10 times the volume of the one in Blatten, said Schwanghart.
Scientists say that similar to the bursting of lakes formed by retreating glaciers, these collapses reflect a complex intersection of causes, including the effects of climate change. Vanishing ice and permafrost make glaciers more prone to snapping and the underlying bedrock more likely to fracture. A 2015 earthquake in Nepal that killed 9,000 people has also made the southern slopes of the Himalayas more unstable.
The largest hydropower project hit in the August disaster was the 216-megawatt Upper Trishuli 1, whose backers had commissioned extensive technical evaluations before breaking ground. Construction, which began five years ago, is being led by a state-owned South Korean company with financing from a host of international banks, including the World Bank’s International Finance Corporation.
A 2018 environmental assessment report identified an increase in the frequency and severity of floods as the project’s greatest climate risk, and said design modifications had addressed those concerns.
A flood in 2024 revealed some gaps. Part of a workers’ camp was swept away and an early-warning system failed, prompting officials to fix it. That proved effective the following year, helping personnel evacuate when water from a glacial lake thundered down. After that, further work was initiated to assess flooding risks, a World Bank spokesman said.
On Aug. 26, the alert mechanism failed again and the dam was dashed to pieces. Since the project was under construction, at least 1,400 people were on site across various fronts, more than 500 of whom are now missing.
Hydropower planners in Nepal need to rethink their approach and project design, otherwise investing in that sector in the Himalayan region will be a “huge risk,” said Giri Raj Adhikari, the project’s technical director, who is unrelated to Santosh Adhikari. Upper Trishuli 1 was constructed for water flows, not a massive debris-laden surge like in the August disaster, with boulders as big as 25 feet across, he said.
The World Bank spokesman said the project design reflected findings from independent assessments that looked at the risks of flooding and landslides, using studies of the glaciers and glacial lakes and historical evidence available at the time. As more information about the Aug. 26 flood emerges, the bank will consider any implications for risk assessment, monitoring, early warning and emergency response in hydropower projects, the spokesman said.
The surge
The Rasuwagadhi power plant was situated at a spot that made it even more vulnerable. Amid an energy gold rush, as Nepal emerged from a Maoist revolution that ended in 2006, investors began snapping up licenses for hydropower projects.
When the state-controlled Rasuwagadhi Hydropower Company was looking for a project site around the Trishuli, it found many river locations already taken. It ended up in a narrow gorge south of the confluence of two rivers. Commercial operations began in Dec. 2024.
Around that time, unknown to anyone, a cluster of small lakes atop the Purepu Glacier, nearly 17,000 feet above sea level, had begun growing. Over the next few months, they rapidly merged into a single supraglacial lake. In early July 2025, it gave way.
Sometime after 3 a.m. that July 8, the roar of the incoming surge jolted Santosh Adhikari awake. Within minutes, he and his crew were scrambling up the mountainside in darkness. There were no visible signs of bad weather that day, no flood had been forecast, and no safety measures were in place, Adhikari later wrote on his Facebook page.
As they watched from the slope above, the waters submerged their living quarters and swept away pickup trucks. Gantry cranes were washed away, silt and boulders jammed the headworks, and floodwaters entered the power house, knocking the plant offline. Ten hours later, a military helicopter airlifted the stranded team to safety.
He discussed the risks of his job with his older brother. Adhikari had two boys, one just a month old. But Adhikari didn’t want to abandon his post, said his brother, Tuka Nath Adhikari, a high-school science teacher.
He had quickly risen through the ranks to become the plant’s manager and felt hydropower was his calling. He frequently wrote Facebook posts about Rasuwagadhi’s trials and triumphs, and wanted to revive it. Besides, the brothers planned to build a house in Kathmandu, the country’s capital, and Adhikari’s job paid well.
The flood seemed like such a freak event that at the time, it was difficult for anyone at the company to imagine that a worse one could come—let alone the following year, said its former CEO Satya Ram Jyakhwa. “We are thinking that was the most dangerous flood” that could come, he said.
Amatya, the company’s acting chief executive, said the project was designed to survive intense, low-probability floods, but not glacial lake outbursts and catastrophic debris flows. After last year’s surge, executives urged local government officials to liaise with their Chinese counterparts across the border to help install early-warning instruments upstream that could save lives, but achieved no breakthrough, he said.
By December, part of the Rasuwagadhi facility was back online, recovering fully in June this year. Then, on the morning of Aug. 26, the immigration and customs office just north of it was engulfed in a massive wave that had traveled at a speed of more than 160 feet per second, according to Chinese state media. Adhikari had no warning.
At the Upper Trishuli 1 project lower down, Rabindra Hamal got a call from a colleague: Run. Outside, the sky was clear and the river appeared calm. Hamal piled into a pickup truck with co-workers and sped downriver. Glancing back half a mile later, he saw a towering wall of brown water churning through the gorge.
Abandoning the vehicle, the group clambered up the rocky mountainside, grabbing onto boulders and grass to haul themselves up. Though the main river channel lay some distance away, the surge had overflowed its banks, extending to the slope where Hamal was crouched behind a large rock.
The waters slammed into the rock, leaving Hamal covered in mud and water, but still breathing. Two others from his group didn’t make it. Moments later, the flood broke through the gates of the next hydropower facility with a bang, like a bomb blast, Hamal said. “Nobody expected this kind of flood, not a single person,” he said.
Gunnam Jaykrishna, a mechanical engineer from India, was deep in the main access tunnel. He knew nothing about the flood until he emerged.
He tried again and again to call his wife and 18-month-old daughter in Salletar, a settlement where many workers at Upper Trishuli 1 live. He couldn’t get through. If workers there had been warned when the first project was hit, so many lives could have been saved, he said.
He fears returning to hydropower work. “This is not just about one river,” he said.
Two days after the surge, there was still no word about Adhikari. His brother, Tuka Nath, embarked on a desperate search. The helicopter he was on, hired by Rasuwagadhi, was unable to land at the location of the project, which was a muddy wasteland. It dropped him off at a nearby town.
He and three others trudged through the jungle for hours but couldn’t find their way and spent the night in a goatherd’s shed. They set out again the next day, battling leeches and surviving on instant noodles, hiking through the mountains without any luck. On the third day, they climbed to a high point from which they could see the flattened area where his brother’s two-story residence building once stood.
“My mind stopped working,” said Tuka Nath. “I felt it was too late.”
The path down was rocky and difficult to cross. He returned, heartbroken.
Write to Niharika Mandhana at niharika.mandhana@wsj.com, Krishna Pokharel at krishna.pokharel@wsj.com and Tripti Lahiri at tripti.lahiri@wsj.com
