Scientists have explained the causes of the catastrophic flood on the border between Nepal and China
The catastrophic flood that occurred in late August on the border between Nepal and China was caused by a complex chain of natural processes. According to more than 20 international scientists, the effects of climate change may have exacerbated some of these factors.
On August 26, a massive mass of rock and glacial ice, approximately 600 meters wide, broke away from Mount Langtang Lirung. It cascaded about 2,100 meters down into the valley.
The impact was so powerful that its force is comparable to a 5.2-magnitude earthquake. As a result of the collapse, the ice melted almost instantly.
The torrent of water, ice, and debris swept up moisture-saturated sediment and likely collided with ice at the bottom of the valley. This created a powerful wave that traveled more than 30 km downstream at high speed, destroying towns, roads, and bridges.
Researchers from World Weather Attribution believe that this disaster cannot be explained by a single extreme weather event alone.
According to their assessment, the avalanche was the result of a chain of interconnected processes that may have been exacerbated by global warming over the course of decades.
One contributing factor may have been the magnitude 7.8 earthquake that struck Nepal in April 2015. It triggered a rock-and-ice avalanche on the mountain’s southern slope and likely weakened the rock formations.
After that, landslides became more frequent in the area, which could have further affected the stability of the slopes.
Researchers cite rising temperatures in the Himalayas as another important factor.
In the region, the altitude at which the temperature drops to 0 °C has risen by more than 100 meters over the past decade.
As a result, permafrost—a mixture of ice, rocks, sand, and soil that helps hold the rock together—is gradually thawing in the high mountains.
“The thawing of the permafrost reduces the strength of the rock and allows more water to penetrate the slope,” explained hydrologist Walter Immerzel.
Changes in the Langtang-Lirung Glacier may also have affected the slope’s stability.
Over the past few decades, the glacier has noticeably thinned and shrunk, especially since 2010. Meltwater may have seeped into cracks in the rock, further weakening it.
Weather may also have played a role. Last fall, the region received an unusually large amount of snow, and July and August were the warmest on record for the area.
According to scientists’ calculations, due to climate change, summer temperatures in this region are now approximately 1.5 °C higher than before.
At the same time, the researchers note that establishing a clear link between global warming and changes in snowfall and precipitation is much more difficult. The reason is the limited ability to conduct observations in hard-to-reach areas of the Himalayas.
The scientists concluded that climate change played an important role in creating the conditions for this disaster, although it was not the sole cause.
According to their estimates, the scale, speed, and complexity of the avalanche were so unusual that even existing early-warning systems would not have provided enough time to evacuate the population.
CNN reports on this.
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