A mountain collapse unleashed a wave with extraordinary force, but the deeper story lies in the slow changes that weakened the landscape for years.
A powerful flood along the Nepal–China border in late August may have resulted from several natural processes intensified by human-caused warming. That is the conclusion reached by more than 20 international scientists in a new analysis.
As highlighted by CNN
A rock-and-ice avalanche from Langtang Lirung Mountain swept into narrow mountain valleys, destroying towns, roads, and bridges. According to the estimates provided, at least 1,300 people were killed, while more than 5,000 are still considered missing.
On August 26, a mass of rock and ice approximately 610 meters wide broke away from the mountainside. It fell about 2,134 meters into the river channel, releasing energy comparable to that of a magnitude 5.2 earthquake.
The force of the impact melted some of the ice almost instantly. The flow swept up water-saturated sediment and likely collided with buried ice at the bottom of the valley. This caused a powerful wave to form, which rapidly traveled more than 32 kilometers downstream.
This was an unprecedented disaster for the Himalayas.
– Walter Immerzeel, a mountain hydrologist at Utrecht University
How climate change may have intensified the collapse
Researchers from World Weather Attribution, an initiative that analyzes the influence of climate change on extreme events, believe the tragedy was not caused by a single weather event. In their assessment, various factors linked to warming caused by fossil fuel combustion accumulated over decades.
One possible factor was the magnitude 7.8 earthquake that struck in April 2015. It triggered a rock-and-ice avalanche on the southern slope of the mountain and likely weakened the massif. Landslides became more frequent in the area afterward.
The scientists identified several processes that may have affected the stability of the slope:
Before the collapse, the region received unusually heavy snowfall, particularly in October and early November of the previous autumn. July and August were the warmest months in the entire period of local observations, which may have accelerated the melting of the ice.
Historical data and climate models indicate that temperatures in July and August in this area are approximately 1.5°C higher because of global warming. The average annual temperature has risen by 2°C, well above the global average.
At the same time, the researchers were unable to establish a clear link between warming and an increase in snowfall and precipitation. They attribute this to the difficulty of taking measurements in the mountainous regions of the Himalayas.
There is no doubt that human-caused climate change played a role in creating the conditions that preceded the disaster.
– Friederike Otto, professor of climate science at Imperial College London
Could warning systems have prevented the tragedy?
According to the researchers, this collapse was distinguished by its scale, speed, and complexity from all similar events the region had previously experienced. In their view, no existing early-warning system could have given people enough time to prepare.
The scientists warn that without rapid cuts to emissions from fossil fuel combustion, disasters of this scale could happen again. At the same time, the analysis, prepared using methods from peer-reviewed research, had not undergone independent scientific peer review at the time of publication.