Scientists link Nepal-China border flood to climate-induced permafrost thaw and prior earthquake
A team of international researchers says the August 2023 rock-ice avalanche and flood on the Nepal-China border resulted from a combination of factors, including a 2015 earthquake, permafrost melt and glacier loss, all amplified by human-driven warming.
More than 20 scientists from the World Weather Attribution network have concluded that the deadly August avalanche and flood on the Nepal-China border were the product of several interacting processes rather than a single weather event. The collapse of a 2,000-foot-wide section of rock and ice from Langtang Lirung mountain on August 26 released energy comparable to a magnitude 5.2 earthquake and generated a fast-moving flood that traveled over 20 miles downstream, killing at least 1,300 people and leaving thousands missing.
The researchers note that the mountain slope was likely weakened by the 7.8-magnitude earthquake that struck Nepal in April 2015, which triggered earlier rock-ice movement and increased landslide activity in the area. Subsequent warming has raised the altitude of the 0 °C isotherm by more than 320 feet per decade, eroding permafrost that normally binds rock, soil and ice together. "Thawing permafrost reduces the rock strength and allows more water to penetrate into the slope," said Walter Immerzeel, a mountain hydrologist at Utrecht University.
Glacier observations show that the Langtang-Lirung glacier has thinned markedly since 2010, creating additional meltwater that can infiltrate rock fractures. The region also experienced unusually heavy snowfall in October-November 2022, followed by record-high July-August temperatures in 2023, which the team estimates are about 1.5 °C warmer than they would have been without human-induced climate change. "There is absolutely no doubt that human-induced climate change played a role here in the preconditioning of the disaster," said Friederike Otto, a climate science professor at Imperial College London.
The analysis, which follows peer-reviewed methods but has not yet undergone formal peer review, finds no clear link between climate change and changes in precipitation, citing measurement challenges in the Himalayas. The authors caution that existing early-warning systems were insufficient for an event of this magnitude and speed, and they warn that similar large-scale disasters could become more frequent without rapid reductions in fossil-fuel emissions.