Rivers are known to naturally meander, change courses, braid and branch. But as rising temperatures melt glaciers and thaw frozen ground, the courses of Himalayan rivers are shifting and changing shape much more rapidly than before, according to a new study published in the journal Science. The rising instability of the rivers could pose a risk to water security and critical infrastructure, researchers say.
The Himalayas, often referred to as the “Water Tower of Asia”, provide vital water resources for nearly 2 billion people downstream. But according to the study, in the upper high Himalayan region, where several important river basins originate, temperatures have risen nearly twice as fast as the global average in the past four decades.
The researchers studied three upper high Himalayan river drainage basins: Yarlung Tsangpo, Indus and Ganges. The sources of these rivers occur at elevations of nearly 5,000 meters (16,404 feet), where there is extensive glacier, ice cover and permafrost. Meltwater from these glaciers and permafrost, which is sensitive to climate warming, forms the rivers’ primary water supply.
To find out how climate change is shifting and reshaping these upper high Himalayan river basins, the researchers analyzed 40 years of satellite imagery. In particular, they measured 1,079 river bends, covering roughly 1,582 kilometers (983 miles), from 1980 to 2020. Since valleys can confine and influence river movements, the researchers chose unconfined bends or meanders that flowed freely through the landscape for their analysis.
Their analysis found that the rivers’ courses were shifting sideways faster from 2000-2020 compared to 1980-2000. There was also a significant increase in new channels and shortcuts created by the rivers over the decades. These are signs of rising river instability, the authors say.
The study attributes the instability to cryosphere degradation, suggesting that as temperatures rise, the thawing of permafrost weakens riverbanks while increasing meltwater and sediment loads, making the landscape more prone to erosion.
“The upper high Himalayas stand out as a region where climate warming and channel migration interact strongly,” said study lead author Zhongpeng Han of the China University of Geosciences, Beijing, in a news release. He noted that the region serves as a natural laboratory for studying climate-driven changes in river movements and shape.
The researchers warn that the increasingly unstable rivers pose significant risks to water security and critical infrastructure like roads and bridges.
“For the billions who rely on Himalayan water sources, the acceleration of river dynamics documented in our study poses implications for water security, sediment-related hazards, and the stability of riparian infrastructure,” said study co-author Chengshan Wang of the China University of Geosciences.
Banner image: Using satellite imagery and field observations spanning four decades, researchers found that as global temperatures rise, rivers across the upper high Himalayas are becoming more unstable. Image courtesy of “Steingletscher Moods” by ScrewJ Image (CC BY-NC-SA).