Climate change boosted risk of devastating Himalayan flood

Climate change is leading to conditions that can destabilise high-mountain rock and ice, strengthening prospects for disasters such as this week's Himalayan flood along the border between Nepal and China's Tibet that killed 165, scientists say.

At least 800 foreigners are among the nearly 1,500 missing, authorities said on Thursday, a day after a massive wall of mud and rock collapsed into a Himalayan river, sending catastrophic floods through towns and valleys.

"Climate change is generating conditions that can destabilise high-mountain rock and ice," said Simon Cox, chief scientist at the Mountains to Sea programme at Earth Sciences New Zealand.

That in turn makes collapses and cascading hazards of the kind seen this week more frequent, he added.

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Exact cause of disaster still being analysed

While the exact cause of Wednesday's disaster is still being analysed, scientists say it probably began with a massive ice-rock avalanche on the northern slopes of Nepal's Langtang Lirung peak into the Lhende Khola river on the Tibetan side.

At least six major hydropower plants and infrastructure at the Gyirong Port trade hub were damaged in a multi-stage hazard chain across borders triggered by the initial collapse.

It also altered river channels more than 100 km (62 miles) downstream, near the Indian border.

While experts caution against describing climate change as the sole, immediate trigger for Wednesday's collapse, they say that rising temperatures and melting glaciers probably played a role in the disaster.

Warming can reduce ice support on steep slopes, boost meltwater, and change patterns of freezing, thawing and rainfall, which can weaken mountainsides and make large collapses more likely in some spots, Cox added.

Similar surges in recent years were on smaller scale

Similar catastrophic surges have convulsed the region in recent years, but on a smaller scale.

These range from a 2025 flood at Gyirong on the Tibet-Nepal border to a glacial lake outburst in the Sherpa village of Thame in 2024, preceded by another in India's northeastern state of Sikkim in 2023.

Floods, landslides, avalanches, and droughts are increasing in frequency and ferocity across the Hindu Kush mountain range.

The accelerating changes to water, land and air pose a major threat to people in the region, the Nepal-based International Centre for Integrated Mountain Development says.

Rising mountain temperatures make the cryosphere, or the ice-clad part of the earth's surface, far more vulnerable than in the past, said Farooq Azam, senior cryosphere specialist at ICIMOD.

He said he believed that heavy snow melt, coupled with seismic activity, probably triggered the initial rock and ice avalanche that cascaded into Wednesday's downstream flash flood.

Long-term trend appears stark

The long-term trend appears stark, with the United Nations saying in 2023 that global warming caused Nepal's snow-capped mountains to lose close to one-third of their ice cover in just over 30 years.

It added at the time that glaciers in Nepal had melted 65% faster in the prior decade than in the preceding one.

Wednesday's disaster could be a classic example of a "compound event", said Benjamin Horton, dean of the School of Energy and Environment at the City University of Hong Kong.

That happens when an earthquake interacts with climate-driven changes, such as glacier loss, thawing permafrost, and slope instability, to "create a more complex and damaging disaster than would occur from any one factor alone", he added.

Understanding these cascading risks will be essential for improving resilience in high mountain regions, Horton said.