What is happening to the Qinghai-Tibet Plateau under the influence of global warming?

The latest research by the team led by Academician Yao Tandong of the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, shows that under the influence of global warming, the lake effect of the Qinghai-Tibet Plateau is showing an increasing trend. Through data analysis and simulation of 24 lakes such as Nam Co and Selin Co, typical lakes on the Qinghai-Tibet Plateau, and 12 large lakes with an area of ​​more than 300 square kilometers, researchers show that lake effect snowfall on the Qinghai-Tibet Plateau has a significant impact on downstream areas. Under the influence of future climate warming, it is expected that the intensity of lake effect snowfall triggered by the southward movement of the westerly circulation will increase. The snow disaster effect caused or aggravated by lake effect snowfall in the future needs to be continuously paid attention to, studied in depth, and countermeasures proposed.

Large-scale lake-effect snowfall occurs on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau, with an average altitude of more than 4,000 meters, has the world's largest group of plateau lakes, with a total lake area of ​​about 50,000 square kilometers. Among them, Selin Co and Nam Co are the two largest lakes in the Tibet Autonomous Region, with an area of ​​more than 2,000 square kilometers each. In autumn and winter, when cold air passes over relatively warm unfrozen lakes, snowfall usually occurs in the downwind area of ​​the lakes. This phenomenon is called lake effect snowfall. The physical mechanism of the lake effect is that due to the blocking effect of the unique terrain of the Qinghai-Tibet Plateau, the mid-latitude westerly jet stream moves from the north to the south of the Qinghai-Tibet Plateau around October and prevails between 30° and 35°N above the Qinghai-Tibet Plateau. The southward movement of the westerly jet stream is accompanied by the invasion of cold air, which affects dozens of unfrozen lakes, triggering lake effect snowfall and bringing a series of consequences.

Lake-effect snowfall on the Qinghai-Tibet Plateau is showing an increasing trend

Through comprehensive remote sensing and reanalysis data, researchers found that the southward movement of the westerly circulation in autumn caused a sharp drop in temperature, triggering the lake effect of the lake group on the Qinghai-Tibet Plateau, thereby causing heavy snowfall.

Figure 1 The southward movement of westerly winds in 2013 triggered the lake-effect snowfall process over Selin Co, the largest lake in Tibet

Figure 2 The southward movement of westerly winds in 2013 triggered the lake-effect snowfall process over the Qinghai-Tibet Plateau lakes

The researchers' study also found that the intensity of lake-effect snowfall triggered by the southward movement of the westerly circulation is positively correlated with the area, wind speed and longitude of the 12 large lakes (area greater than 300 square kilometers). Larger lakes have longer wading distances, allowing cold continental air masses to pass through open waters and carry more water vapor evaporated from warm lakes, which promotes the development of lake-effect snowfall events in areas downwind of the lakes. Secondly, higher wind speeds will lead to increased evaporation on the lake surface. In addition, under the influence of the westerly wind, as the longitude of the lake moves eastward, the lakes closer to the east in longitude will be affected by the interaction between lakes caused by the westerly jet stream from west to east, which intensifies the lake-effect snowfall.

Figure 3 Relationship between lake effect snowfall intensity and lake area, lake surface wind speed and longitude from 2002 to 2017

The researchers' research further found that under the future climate warming scenario, the intensity of lake effect snowfall triggered by the southward movement of the westerly circulation is expected to increase. Snow disasters caused or aggravated by future lake effect snowfall deserve continued attention and in-depth research.

Figure 4 The intensity of lake effect increases under the background of global warming

The disaster effect of enhanced lake-effect snowfall on the Qinghai-Tibet Plateau is an urgent issue for sustainable social development

The disastrous effects of lake-effect snowfall are a global problem. It is particularly evident in the Great Lakes and Salt Lakes of North America, where snow depths can reach 30 to 200 centimeters, causing a significant impact on the economic and social life of residents in the downwind areas of the lakes. Lake-effect snowfall on the Qinghai-Tibet Plateau also causes major disastrous consequences. In 2013, an autumn snowstorm was observed in the downwind area of ​​Nam Co (an area of ​​about 2,015 square kilometers), with a snow depth of about 45 centimeters, which is comparable to the snow depth record (about 36 centimeters) observed in North America such as Salt Lake (an area of ​​about 4,400 square kilometers) on December 7, 1998. There are currently about 10,000 permanent residents living in the downwind areas of the two lakes, Selin Co and Nam Co, and there are about 355,000 livestock. The economic and social impacts that may be caused by the enhancement of lake-effect snowfall should not be underestimated, and the society needs to pay close attention and propose response plans.

Dai Yufeng, Wang Tao, Sheng Yongwei, et al. Westerly-triggered lake-effect snowfall enhanced with climate warming over the Tibetan Plateau. Science Bulletin, 2024, 69(7): 968-977