As Himalayan glaciers melt faster, rivers become increasingly unstable

The Himalayas are losing glacier stability at the same time that their rivers are becoming harder to predict. Flash floods triggered by glacial collapse in Nepal and Tibet last week have renewed attention on a mountain range that contains more glaciers than any region outside the polar areas.

The glaciers act as Asia’s “water tower,” feeding rivers that supply water to 2 billion people. But their melt is also sending more water and sediment downstream. Climate change has doubled the rate of glacier melt, while temperatures in the high-altitude Himalayas have risen twice as fast as the global average since the 1980s, according to reports cited in the study.

Researchers led by scientists at China University of Geosciences in Beijing examined satellite images and field observations covering three major upper-Himalayan basins. They tracked 1,079 bends along 1,582 kilometers of river channels between 1980 and 2020.

The results showed that river changes accelerated over the four decades. The rate at which meanders moved increased by 33%, while lateral migration nearly doubled. River disruptions rose 115%, changes in course increased 77%, and channel bifurcations, where rivers split into separate paths, climbed 97%. An index measuring changes in a river’s overall shape doubled, while travel time fell 40%.

Melting glaciers increase river volume and sediment, while thawing permafrost weakens banks that once resisted water pressure. Rivers can then move faster, break through their banks and divide into more channels. The resulting flooding and erosion threaten infrastructure, farmland and settlements in the mountain region.