World Weather Attribution scientists say fossil fuel-driven warming played a role in the occurrence and intensity of Nepal’s August 26 cascading flood disaster.
The disaster began when rock and ice collapsed from a glacier on Langtang Lirung, triggering a fast-moving flood of water, ice and debris in the Lhende river.
Researchers said climate change acted as a destabilising factor on a slope already weakened by geology, the 2015 Nepal earthquake, glacier retreat and thawing permafrost.
The study said the event was beyond the design and predictive limits of existing risk-reduction measures, highlighting the limits of adaptation in rapidly warming mountain regions.
Warming of the atmosphere caused by greenhouse gas emissions from burning fossil fuels, and the consequent changes in climate and geology, played a role in the occurrence and intensity of Nepal’s cascading flood disaster on August 26, 2026, according to an attribution analysis by World Weather Attribution (WWA).
WWA is an international group of scientists that analyses and quantifies the role of warming and climate change in the frequency, intensity and duration of extreme events and related disasters.
The researchers said the Nepal disaster was “beyond the design and predictive limits of existing risk reduction measures”, and that no existing early warning system could have provided enough lead time or prevented the scale of impacts seen in the worst-affected areas. They said this highlighted the limits of adaptation in a rapidly warming mountain region.
The disaster began when a mass of rock and ice collapsed from a glacier on Langtang Lirung mountain, near the Nepal-China border, triggering a chain of events that released a catastrophic flood into the Lhende river on the morning of August 26.
The flood carried huge volumes of water, ice and debris into downstream rivers, travelling at speeds of up to 188 kilometres per hour and washing away villages and hydropower projects in its path.
As of September 12, 1,386 people had died, 5,130 remained missing and 13,728 had been rescued.
The humongous volume of water in the flood came from several sources. The first was water released from the melting of glacial ice that fell from the mountain at an elevation of 5,150 metres above mean sea level onto the valley floor at about 3,750 m. This water was then carried forward by the river.
When the rock and ice fell onto the valley floor, it generated enormous energy, producing seismic waves that were recorded as an earthquake-like signal by detectors. The mechanical energy of the moving debris melted glacial ice, which became the primary source of water in the flood.
A second source was water stored beneath the glacier. A third was water from thawing permafrost. A fourth came from the melting of buried ice on the valley floor, while a fifth came from the pressure wave generated by displaced river water ahead of the debris flood.
The combination of ice, rock, water and sediment travelled about 35 km downstream, causing widespread destruction. The resulting floodwater travelled much farther through the Bhote Koshi and Trishuli river systems, reaching areas close to India.
The WWA study analysed the disaster as a combination of factors, rather than as a single extreme weather event. The research team included experts in glaciology, mountain hydrology, climate science, humanitarian aid, seismology and social science.
The scientists examined why the initial rock and ice collapse happened, and what role warming and climate change may have played. They found that while the underlying geological structure controlled where and how the slope failed, longer-term warming and changing precipitation from snow to rain may have reduced slope stability.
This could have happened by weakening ice-filled fractures and rock-ice contacts, and by increasing water pressure. “Climate change is thus best understood as a destabilising factor acting on a pre-existing geological predisposition, rather than the fundamental cause of the failure,” the scientists said.
The geological structure of Langtang Lirung had already been conditioned for collapse by the 7.8 magnitude earthquake that struck Nepal in 2015, according to the analysis.
Further weakening of the slope may have occurred as warming pushed the freezing line higher in the region, allowing permafrost deep in the bedrock to thaw. The scientists estimated that the freezing line has moved upward by about 100 m per decade during the monsoon and post-monsoon seasons.
Another factor was the thinning of the glacier over time, also linked to warming. As the glacier retreated, it removed surrounding ice that had helped stabilise the slope. “Since 2010 the rate of recession of the Langtang-Lirung glacier extent has accelerated, increasing from 0.5 per cent per annum over the previous two centuries to 1-2.3 per cent per annum in the past 16 years,” the report said.
Immediate weather conditions in July and August also added to the risk. Average temperatures in the region were much higher than normal, with some days recording anomalies of 5 degrees Celsius to 10°C. The two-month period was the hottest on record locally, according to the analysis. The 12-month period from September 2025 to August 2026 was also unusually warm.
Long-term warming in the region has been higher than the global average. While global warming since the pre-industrial period is about 1.5°C, the region has warmed by about 2°C annually, and by as much as 3°C in winter months.
Warmer temperatures also increase the share of precipitation falling as rain rather than snow at higher elevations. “Rain produces an immediate liquid-water input to the slope, whereas snowfall temporarily stores water at the surface. Intense or prolonged rainfall can therefore rapidly increase water supply to fractures and potentially increase fracture-water pressure,” the researchers said in the report.
“At the rock-ice-avalanche location, stations recorded exceptionally high precipitation during October 2025, which combined with subsequent warmth may have been a source for meltwater during the following spring and monsoon seasons,” they added.
The scientists said that fully attributing the entire event to warming would require more evidence linking atmospheric conditions to subsurface temperatures, fracture-water pressures and the mechanical evolution of the slope.
However, they said rapidly rising temperatures, driven by fossil fuel emissions and increasing at a rate beyond the global mean, are making such hazards in the Himalayas more likely and more severe.
“This report isn’t a traditional World Weather Attribution study because we aren’t looking at a single extreme weather event but a multi-stage mountain disaster with many factors influencing causality,” said Friederike Otto, professor of climate science at Imperial College London. “Yet the climate justice reality is as sharp as ever. Communities in Nepal are paying with their lives for a crisis driven by fossil fuel emissions thousands of miles away,” she said.
Manjeet Dhakal, director of Climate Analytics South Asia, said the scale of the disaster was testing Nepal’s response capacities and the limits of adaptation. “Every fraction of a degree of warming matters,” he said.
“Science must now drive urgency: deeper and faster global emission reductions, greater investment in understanding complex mountain risks, strengthened monitoring and early warning, climate-resilient development, and international climate finance support at the scale and speed that frontline countries like Nepal need,” he stated.