Climate change caused Nepal floods, but a 2015 earthquake may have contributed

A new study has blamed human-induced global warming for the catastrophic Nepal floods, saying the rising temperatures had thawed permafrost and thinned glacier ice that had been holding the mountainside together for centuries. Led by the World Weather Attribution (WWA), the study states that decades of warming had weakened the slope that collapsed on August 26, setting the stage for a disaster that went beyond the capacity of the existing disaster adaptation systems.

They also found during their course of the study that the freezing line in the Himalayas has been moving up by 100 metres every decade. This is the point above which the ground remains permanently frozen. After the devastating floods killed over 1,300 people in Nepal and Tibet, scientists have been trying to understand what transpired on the day. Every study done so far has blamed climate change for it. Glaciers are melting in the Himalayas, which can cause similar floods in the future.

"Climate warming, as a result of humans burning fossil fuels, is melting ice and snow in the Himalayas, decreasing glacier coverage and thawing permafrost," which destabilises the mountainsides, Bethan Davies, professor of glaciology at Newcastle University, said.

Mechanism of Nepal floods similar to Chamoli disaster

They stated that even though the scale of the disaster was unlike anything seen before, the signs of an imminent threat were always there. Walter Immerzeel, a mountain hydrologist at Utrecht University, told reporters, “The mechanism of the disaster is comparable to what happened in India in Uttarakhand, which is called the Chamoli disaster.”

Comparing the two disasters, the team further said that in the Chamoli incident, the material that flowed down was only a fifth of what was seen in Nepal and the impact was much less, making the Nepal tragedy “unprecedented.”

2015 earthquake could have been a reason as well

They also presented another possibility. In 2015, a magnitude-7.8 earthquake struck the Langtang Lirung mountain on Nepal's northern border, where the glacier collapse occurred this year. This may have weakened the slope that gave way in August. The intense shaking of the ground probably damaged the bedrock and increased the number of fractures. However, there is no proof that this happened, Immerzeel said.

He added that these two factors combined may have had an impact, although they are sure that the changing climate was definitely responsible for the Nepal disaster.

Hotter monsoon months before Nepal tragedy

The researchers further stated that climate change had increased the temperatures in the months of July and August, which were the highest ever recorded in the region. During the monsoon, it was 1.5 degrees Celsius warmer, and the annual temperature had spiked by nearly 2 degrees Celsius.

Professor Friederike Otto of Imperial College London said that even though they did not run a specific attribution model on the Langtang Lirung glacier's thinning, glacier thinning is the only cause of the tragedy that unfolded on August 26.