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Average temperatures in high elevation areas have risen twice as fast as the global average, causing more river runoff and sediment flows, and the trend could worsen – ScienceDaily

Rivers flowing from the Tibetan Plateau and the surrounding high Asian mountains that are home to one-third of the world’s population have seen a rapid increase in annual water and sediment runoff since the 1990s, and the volume of sediment washed downstream. could more than double by 2050 under the worst case scenario, a team of scientists has found.

The cause is an “amplified warming”: since 1950, the region of Asia of the high mountains, or the region of Asia containing five mountain ranges, including the Himalayas and the Hindu Kush around the Tibetan plateau, s ‘is warmed by about 2 degrees Celsius, which is double the warming. worldwide. This warming precipitates melting glaciers and thawing permafrost, while annual precipitation is also increasing, the researchers note.

“These findings have far-reaching implications for hydroelectric, food and environmental security in the region,” the researchers observe. The results also highlight the underestimated importance of sediment fluxes and have implications for potential changes in the global carbon cycle, they add.

The research, published today in the journal Science, is led by the National University of Singapore and includes three researchers from the University of Colorado Boulder, including Irina Overeem, Jaia Syvitski and Albert Kettner, all researchers from the Arctic and Alpine Research Institute. Overeem is also Associate Professor of Geological Sciences at CU Boulder, and Syvitski is Emeritus Professor of Geological Sciences.

Scientists analyzed observational data for runoff and sediment flows from 28 headponds over the past six decades.

Sediment flow is the mass of sediment that passes through a specific point in a river basin over a period of time, “like trucks of sand being transported, in this case by water,” Overeem said. Although river runoff, the amount of water entering a river system, and the flow of sediment both increase, they increase at different rates.

In the river basins studied by scientists, runoff increased by about 5% per decade, while sediment flow increased by about 12% per decade.

Overeem explained that variability is affected in two ways: “With melting glaciers and thawing permafrost, new sources of sediment, which were previously frozen in place in the landscape, can now collapse into the river. In addition, if more precipitation triggers more flooding. , you’ve suddenly crossed a threshold and you can pick up so much more sediment “than average conditions.” If you increase the source and proportion of a few of these extreme events, you will get disproportionately much more sediment. So maybe that’s what’s going on in this system. “

River sediments can benefit densely populated areas like Bangladesh, where sediments help maintain the coastal zone. But in other regions such as Tibet and Nepal, which have hydroelectric power stations, rising sediment levels can wear down dam turbines and fill reservoirs with sand and silt.

By harming existing or planned hydropower projects and reducing irrigation capacity, increased sediment flows may thus “threaten the region’s food and energy security,” the authors write. Additionally, increasing levels of sediment, which can carry nutrients, pollutants and organic carbon, can have implications for water quality and flooding, potentially affecting millions of people.

Research on the Asian high mountain watershed has been aided by the exceptionally good long-term records of streamflow and sediment flow, Overeem said, adding that there are no sets. data of similar quality for Greenland or the entire Arctic.

In the Arctic, scientists have also recorded increases in water flow from melting ice and increased precipitation, but have few measurements of sediment flow.

“What is happening on the Tibetan Plateau can also be happening in the Arctic, but we just don’t have enough long recordings there and observational support to really know it yet,” he said. declared Overeem.

The research was led by Dongfeng Li and Xi Xi Lu of the National University of Singapore.

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