What caused the rainstorm?

Heavy rain is caused by sufficient water vapor, strong and lasting upward movement of airflow and unstable atmospheric structure. The favorable combination of various scales of weather system and underlying surface, especially topography, can produce heavy rain. The main weather systems that cause large-scale rainstorm in China are fronts, cyclones, shear lines, eddies, troughs, typhoons, easterly waves and intertropical convergence zone. In addition, thermal thunderstorms will also cause short-term and small-scale heavy rains in arid and semi-arid areas.

Rainstorms often fall from cumulonimbus clouds. The condition for the formation of cumulonimbus clouds is that the atmosphere contains enough water vapor, and there is a strong upward movement to transport the water vapor rapidly upward. The water droplets in the cloud are constantly affected by the upward movement until the upward airflow can't support them, and they drop sharply to the ground.