China News Service, Beijing, November 21 (Reporter Sun Zifa) As the "third pole of the earth" and the "roof of the world", the changes in the ecological environment of the Qinghai-Tibet Plateau have long attracted attention.

Monitoring in recent years has shown that the water level of lakes in the western Qinghai-Tibet Plateau has risen significantly during the winter when the lakes freeze. What causes this?

What will be the impact?

　　The Qinghai-Tibet Plateau Institute of the Chinese Academy of Sciences (Qinghai-Tibet Plateau Institute of the Chinese Academy of Sciences) announced on the 21st that the environmental change and multi-sphere process team and collaborators of the institute have used the latest five-year lake water level and hydrometeorological monitoring data in the western Qinghai-Tibet Plateau to complete targeted research. The study found that groundwater recharge leads to a significant rise in lake water level during the winter lake freezing period, which can significantly affect the seasonal and interannual variation characteristics of lake water level in the western Qinghai-Tibet Plateau.

Schematic diagram of the water cycle in the study area of ​​the Qinghai-Tibet Plateau.

Photo courtesy of the Qinghai-Tibet Plateau Institute of the Chinese Academy of Sciences

　　This research paper, which is of great significance to understanding the water cycle process and the reasons for lake changes in the western Qinghai-Tibet Plateau, was recently published in the international professional academic journal "Geophysical Research Letters" (Geophysical Research Letters).

The data related to this achievement - the lake water level monitoring data in the western part of the Qinghai-Tibet Plateau, has also been shared on the website of the National Qinghai-Tibet Plateau Scientific Data Center.

　　According to Yanbin, the first author and corresponding author of the paper, and an associate researcher at the Qinghai-Tibet Plateau Institute of the Chinese Academy of Sciences, the Qinghai-Tibet Plateau is home to the highest lake group in the world and is one of the most important lake distribution areas in China.

Since the late 1990s, due to the increase in precipitation and the accelerated melting of the cryosphere, the lakes in the inland area of ​​the Qinghai-Tibet Plateau have expanded significantly, affecting the regional ecological environment and surrounding infrastructure, which has attracted widespread attention from Chinese and foreign scholars.

　　There are many factors affecting the water balance of lakes, including atmospheric precipitation, lake surface evaporation, melting of the cryosphere, groundwater recharge or seepage, etc.

Previously, due to the lack of systematic hydrometeorological observation data, most academic studies on the water balance of plateau lakes focused on surface water, making it difficult to directly monitor and quantify the recharge of groundwater to lakes.

　　Lei Yanbin pointed out that the water levels of most lakes on the Qinghai-Tibet Plateau remain stable or drop slightly during the winter icing period, but the latest monitoring results show that the lakes in the west of the Qinghai-Tibet Plateau, such as Luma River Dongcuo, Meima Co, Jiezechaka and Longmu However, the water level rises significantly during the icing period of the lake. Among them, the water level of Lumajiangdongcuo and Meimacuo can rise by 0.25-0.35 meters during the icing period of the lake, accounting for about half of the annual lake water level increase. .

The geological structure map of the Qinghai-Tibet Plateau study area and the location of the lake water balance observation points.

Photo courtesy of the Qinghai-Tibet Plateau Institute of the Chinese Academy of Sciences

　　He said that considering factors such as snowfall on the lake surface in winter, runoff into the lake, and evaporation (sublimation) of the lake surface, the research team believes that the main reason for the increase in the water level of the Qinghai-Tibet Plateau during the freezing period of the lake in winter is groundwater recharge, which accounts for the total summer precipitation in the basin. 13%-25%.

The calculation results of the annual lake water balance show that groundwater recharge accounts for 59%-66% of the total inflow into the lake, which shows that groundwater recharge not only plays a key role in the water balance of lakes in the western plateau, but is also an important part of the regional water cycle.

　　Further analysis by the research team found that the formation of groundwater in the western Qinghai-Tibet Plateau may be related to the regional geological structure characteristics.

The bedrock in the study area is dominated by Carboniferous and Permian limestone, and active normal fault zones generated by crustal faults are distributed in each watershed, which is conducive to the downward infiltration of surface water to form groundwater and recharge the lake downstream.

"Glaciers and snowmelt in high-altitude areas recharge groundwater through active fault fracture zones and flow into lakes in low-altitude areas. Due to the stable groundwater recharge and long cycle period, a large amount of groundwater recharge significantly changes the seasonal variation of lake water levels in the western Qinghai-Tibet Plateau. "Lei Yanbin concluded.

(Finish)