Analysis of Flood Disasters and Heavy Precipitation Events in the Sichuan–Chongqing Region in the Summer of 2020

This paper investigates flooding events caused by heavy precipitation and the corresponding 15 heavy rainfall events in the Sichuan–Chongqing area in the summer of 2020 and compares them with the situation in the 2006 drought year. The western Pacific subtropical high (WPSH) was stronger than its climatological mean, and its western edge was beyond 110°E, which is to the west of its climatological position. Since the Qinghai–Tibet high was strong and extended eastward, the upper and lower layers worked together to keep the WPSH stable. The cold air that causes precipitation in the Sichuan–Chongqing region is primarily caused by short waves in the westerlies. Short waves were frequent in the mid-latitudes and influenced the region. The Sichuan–Chongqing region forms an area of major water vapor flux convergence due to the joint influence of the southwesterly flows on the western flank of WPSH and the northerly wind. It provides the best water vapor conditions for the occurrence of heavy rainfall events. Furthermore, the monsoon air stream, which travels from northern India to the east side of the plateau, rounds the south side of the plateau and transports water vapor eastward, forming another important water vapor channel. 2006 was a typical drought year in the Sichuan-Chongqing region, with the fewest heavy rainfall events. In contrast with 2020, the WPSH is easterly this year, the short-wave trough in mid-latitude westerlies is less active, the southwest monsoon is weaker, and water vapor convergence in the Sichuan–Chongqing region is lower.