Why do severe droughts occur again and again in Yunnan?

Yunnan is located in the southwest of China and belongs to a typical subtropical plateau monsoon climate. The annual temperature difference is small, the daily temperature difference is large, the dry and wet seasons are distinct, and the temperature changes obviously with the height of the terrain.

A large part of precipitation in Yunnan comes from the intersection of cold and warm air. After the southwest monsoon broke out in spring and summer, a large amount of water vapor was transported to Yunnan through the Bay of Bengal. As the cold air goes south, once the cold and warm air meet, a large range of precipitation will be formed.

However, due to the high altitude, the warm and humid airflow from other places is easily blocked by mountains, resulting in less rainfall in high altitude areas. Not only that, strong ultraviolet rays at high altitude aggravate the evaporation of water, and the problem of water shortage is hard to imagine.