Climate Change Amplifies Risk of Catastrophic Floods as Death Toll Rises in Nepal and Tibet

Scientists have warned that landslides and glacial collapses like those behind this week’s devastating flooding in Nepal and Tibet are likely to become more common as a result of climate change. Huge waves of water and debris swept away people, roads and buildings, leaving more than 500 dead, most of them in Nepal but a small number in Tibet, and many more missing. Rescue efforts continue, though they are sometimes interrupted by fears of further floods amid concerns that lakes in the area could overflow.

The landslide and glacier collapse is thought to have originated on the Langtang Lirung peak in Nepal, which is part of the Himalayas and around 15km away from the area around the Nepal-China border hit by floods. Himalayan glaciers have been “retreating like crazy” as the climate warms, according to Mike Searle, a professor of earth sciences at the University of Oxford. Along with the retreat of glaciers, a related problem is the thawing of mountain permafrost, with the ice that holds together the shattered rock surface material of mountains melting. This can cause a landslide from the mountain that shears off a glacier, as is thought to have happened this week.

“You have got this precarious glacier perched on the side of a really steep mountain characterised by permafrost that’s melting. You have this cocktail of factors that leads to this totally apocalyptic event,” said Dr Richard Waller, a senior lecturer in physical geography at Keele University in the UK. Images suggest that there was snow a day or two before on the surface of glaciers in the area, said Dr Ethan Lee, a postdoctoral researcher in glacial modelling at the University of Sheffield in the UK, but none on the day of the event. “So a major warming event occurred, potentially allowing water to enter the glacier through crevasses, and if more water enters the base of the ice, it can lubricate it and allow it to slide along the rock more easily,” he said.

Another factor, said Prof Searle, who several decades ago climbed high up the Langtang Lirung peak, is the continued growth of mountains in the area because of tectonic activity. “We know from GPS that these mountains are still rising,” he said. This makes the glaciers steeper and more at risk of falling. The huge waves of water that caused such destruction were probably not an immediate result of the collapse of the glacier, he said, as debris probably created a dam in the river and, behind it, a lake, which may have taken two days to fill up. “Lakes build up behind rock debris flows, and when the lake breaches its dam, it causes catastrophic floods, as we have seen,” Prof Searle said.

Dr Waller said he hoped that this week’s devastation would lead to detailed hazard mapping to identify other locations at risk of similar events, allowing for early warning of potential disasters. He drew a contrast between this week’s events on the Nepal-Tibet border with what happened in May last year at the Swiss mountain village of Blatten, which was evacuated more than a week before it was destroyed by a glacial collapse and landslide. The Khumbu glacier, located on the slopes of Mount Everest, is the only glacier in the area currently monitored in detail, Prof Searle said. He added that more aid is desperately needed, especially to UN organisations, noting that the cutting off of USAID has had a disastrous effect on poor countries like Nepal.

Dr Lee noted that while this week’s events could not be directly linked to climate change, warming has a destabilising effect. There have been previous examples of this, including the 2021 Uttarakhand flood in north-eastern India and the 2022 collapse of a block of glacial ice on Marmolada in Italy. Dr Diana Francis, an associate professor at Khalifa University in Abu Dhabi, stated that glaciers in mountainous regions are even more sensitive to climate change than those in polar regions due to a lack of a protective sea ice margin.