What are the main reasons for the summer drought in July and August in the Yangtze River Basin?

Every April or so, warm and humid air from the Pacific Ocean begins to land in China, where it meets the Mongolian high pressure entrenched in Chinese mainland. The interface between cold and warm air is called front. When cold and warm air meet, it will rise because of the low density of warm air. With the increase of height, the ability of air to contain water vapor will decrease, so it is easy to form precipitation, which is called frontal rain. The rain belt is in South China in early April, and it is called Meiyu in Jianghuai in May and June. Since then, with the direct point of the sun moving northward, the temperature in the northern hemisphere is rising, the warm air is getting stronger and stronger, and the cold air is retreating northward, so the front does not advance northward. At this time, the warm and humid air flow controls the south of China, including the middle and lower reaches of the Yangtze River.

The weather under the control of warm and humid airflow will not produce drought, and it cannot be said that the northward movement of the front leads to the summer drought in the middle and lower reaches of the Yangtze River.

In normal years, July and August in the lower reaches of the Yangtze River are also hot and rainy. However, if the western Pacific subtropical high is stronger than in previous years, it will extend westward to the mainland and control the middle and lower reaches of the Yangtze River in China. Under the control of subtropical high, the weather is dry and rainy, and at the same time, the front will be pushed northward in advance, making the south extremely dry, which is the summer drought in the lower reaches of the Yangtze River.