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Across China: Researchers urge new system to measure precipitation on Qinghai-Xizang Plateau
update:June 13,2024
Chinese researchers have revealed that the amount of precipitation previously measured on the Qinghai-Xizang Plateau has been underestimated considerably, and called for the establishment of a new observation system to measure precipitation on the plateau.

The Qinghai-Xizang Plateau, also known as the Asian water tower (AWT), serves as the source of 10 major Asian river systems and supports the lives of nearly 2 billion people. Obtaining reliable precipitation data over the AWT is a prerequisite for understanding the water cycle within this pivotal region.

Ground-based instrument monitoring is currently believed to be the most important and reliable method for obtaining precipitation information.

However, researchers from the Institute of Tibetan Plateau Research under the Chinese Academy of Sciences and the Beijing Normal University have discovered that the "observed" precipitation over the AWT has been considerably underestimated in view of observational evidence from three water cycle components, namely, evapotranspiration, runoff and accumulated snow.

They found that the three paradoxes appear if the so-called observed precipitation is corrected, namely, actual evapotranspiration exceeding precipitation, unrealistically high runoff coefficients and accumulated snow water equivalent exceeding contemporaneous precipitation.

They explain the cause of precipitation underestimation from instrumental error caused by wind-induced gauge under-catch and the representativeness error caused by sparse-uneven gauge density and the complexity of local surface conditions.

In the Qinghai-Xizang Plateau region, snow makes up a relatively high proportion of precipitation, often accompanied by strong winds. Traditional ground-based monitoring instruments have limited open surface area and closed bottoms, which can lead to updrafts in strong wind conditions.

These updrafts can obstruct raindrops or snowflakes from entering the instruments, resulting in underestimation of precipitation. This wind-induced measurement error is the primary factor affecting the accuracy of precipitation measurements in alpine regions, with errors potentially exceeding 100 percent under extreme weather conditions.

The researchers have called for a re-evaluation of existing instrumental precipitation data and the acquisition of new findings related to water resources, the water cycle and water-related hazards. This includes metrics such as water resource volume, water cycle rates and the proportion of runoff components.

They have also proposed new solutions for precipitation monitoring on the Qinghai-Xizang Plateau, including instrument innovation, site construction and spatial optimization, the comparison of multiple monitoring methods, data assimilation and integration, and deep learning.

The study has been published in the journal Proceedings of the National Academy of Sciences.

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