What is southwest warm and humid airflow?

The southwest warm and humid air flow comes from the Bay of Bengal, and it will produce obvious precipitation when it meets the continental cold air mass. If there is no cold air confrontation, the force is weak, mostly cloudy to cloudy weather, and precipitation will occur when it is vigorously developed. What you said about overhauling Yunnan Reservoir has nothing to do with Three Gorges Reservoir. Even if the Three Gorges Reservoir evaporates excessively, it will not affect the atmospheric circulation.

The most important and direct reason for the formation of this large-scale rain and snow weather process is actually the anomaly of atmospheric circulation, especially in Europe and Asia. When it maintains a stable circulation state for a certain period of time, especially in low latitudes, the Qinghai-Tibet Plateau has a low-value system and Siberia has a relatively high-value system. These two systems have existed in these two regions for a long time. Low-value system brings abundant water systems to southern China, mainly in the southern sea and Indian Ocean, because the warm and humid airflow from southwest affects most parts of China to the north, while the high-value system in the north is stable, mainly bringing cold air from Siberia. Cold and warm air meet in the south of the middle and lower reaches of the Yangtze River, and the density of cold air is relatively high. Relatively speaking, the warm and humid airflow at the bottom slides upward on the heating pad. Because the water vapor formed by the warm and humid airflow itself will condense, some rainy and snowy weather will be formed. Because this cold and warm air meets in this area for a long time, it has caused a long period of rain and snow.

This cold and warm air flow is equivalent to two rivers, one from north to south and the other from south to north. In this case, the two rivers are basically stable and run in a certain channel. In this case, the middle and lower reaches of the Yangtze River always keep the intersection of the two rivers. At the same time, under the background of stable airflow, there will be some small disturbances, such as above the basic airflow, and some small disturbances. After each disturbance, it may bring a rain and snow weather process. In fact, the three rain and snow weather processes in southern China were basically located in the westerly airflow in the south, which disturbed the warm and humid airflow in the southwest for three times and caused three relatively large rain and snow weather processes.