Geography: the causes and countermeasures of drought in the middle and lower reaches of the Yangtze River in China

First of all, the atmospheric circulation system affecting the eastern part of China is extremely significant.

At present, the subtropical high in the western Pacific (10. 14, -0. 12,-1. 17%) is stronger in the north than the multi-year average, and the western ridge is west. There is an anticyclone abnormal circulation in the middle and lower troposphere, which causes no precipitation for a long time and less precipitation, thus forming drought. Due to the influence of subtropical circulation system in previous spring, there will be long-lasting continuous rain in Jiangnan area in spring.

Secondly, the water vapor transport conditions are insufficient, and the water vapor channel cannot be effectively established.

At the turn of spring and summer, with the development of tropical convection system and the outbreak of summer monsoon in the South China Sea, there are usually three channels that affect China's water vapor-Somali cross-equatorial southwest airflow, Bay of Bengal cross-equatorial southwest airflow southward, and southwest airflow from the South China Sea and its eastern vicinity, but the water vapor transport in the three channels is generally weak.

According to the analysis and diagnosis of the water vapor budget of the whole troposphere in the arid area of the middle and lower reaches of the Yangtze River by the Climate Monitoring Office of the National Climate Center, the water vapor loss in this area was large in May, and there was a lack of material conditions for precipitation.

In addition, since the beginning of this year, the cold air activity has been remarkable and powerful, and it is impossible to form a cold and warm convergence situation in the middle and lower reaches of the Yangtze River.