MONITORING SYSTEMS STOPPED TRANSMITTING IN FLOOD

Around 8.32am Nepal time on Wednesday, the deluge blasted through a border crossing in Tibet as people attempted to flee, according to surveillance footage that has become a defining image of the disaster.

Twenty-six minutes later, Parajuli got a call from the chief of Nepal's National Disaster Risk Reduction and Management Authority, alerting him to a flood on the Trishuli River. Parajuli's team found that a border monitoring station had not transmitted any data since 8.40am.

"We also then tried to contact downstream stations, but downstream stations also couldn't post the data," leaving the team to suspect those devices had been washed away, he said.

After contacting local Nepali authorities to confirm the flooding, Parajuli said, his team sent a public alert to mobile phone users at 9.13am.

At least four monitoring stations were destroyed by the flood that rampaged 168km downstream from the Nepal-China border, carrying some 57.4 million cubic metres of water, more than half again as much as normal, according to a Nepali government assessment.

"HUGE GUSH OF MUD COMING STRAIGHT AT US"

Surging floodwaters, which dislodged giant boulders and pulled large buildings into the overflow, damaged 19 bridges and some 40km of highway, and knocked out more than 10 per cent of Nepal's power-generation capacity, according to the Stimson Center.

"It wasn't water. It was a huge gush of mud coming straight at us," said Keshav Prasad Baral of Tupche village, about 25km downstream of the border. "I tried to grab my wife's hand, but she was swept away by the mud."

When part of the glacier broke away, crashing to the valley floor hundreds of metres below, it unleashed high-speed flash floods, according to preliminary assessments by Nepali authorities.

The Hindu Kush Himalayas, home to hundreds of millions of people from Afghanistan to Myanmar, contain the world's largest volume of ice outside the poles, with more than 63,700 glaciers covering nearly 56,000 sq km, almost the size of Croatia, and storing up to 5,700 cubic km of ice.

By comparison, the glacier chunk that caused the latest disaster carried an estimated 5 million cubic metres of ice and rock, according to Basanta Raj Adhikari, director of the Centre for Disaster Studies in Nepal's Tribhuvan University.

Driven by climate change, glacier melt is accelerating as snow cover declines and snowfall becomes more erratic, according to a 2023 study by the International Centre for Integrated Mountain Development.

These changes will increase the likelihood of floods and landslides, as mountain communities also deal with such hazards as sedimentation and erosion, the centre projects.

"WARN OUR PEOPLE, SAVE OUR PEOPLE"

Several of Nepal's major river systems originate in Tibet, then flow through one of the world's most seismically active and flood-prone regions.

Nepal's authorities will seek to work with China to conduct research and build systems to monitor avalanches and the release of water from glacial lakes – major risks for mountain communities – Parajuli said.

He said his department will propose a data-sharing agreement with China, along the lines of an arrangement that Nepal has with neighbouring India, for more frequent information on precipitation and river levels, not just high-precipitation forecasts.

Nepal will seek data every 10 minutes so that "we can warn our people, save our people", he said. "Our main target is we shouldn't miss any future disaster."