Characteristics of the Summer Regional Precipitation Events in the Middle and Lower Yangtze River Basin and Associated Mechanisms

Based on the hourly rainfall gauge data and ERA5 reanalysis data of 1980–2022, this study reveals the characteristics of regional precipitation events (RPEs) over the middle and lower Yangtze River basin (MLYRB) in summer and associated mechanisms. Results show that the RPEs contribute more than 60% of the summer total rainfall over most of MLYRB and dominate the morning diurnal peak, interannual variation, and phased increasing trend for the summer total precipitation over MLYRB. The RPEs mainly occurring under two monsoonal types with shear line (Type1 and Type2; 91.4%) and landfalling tropical cyclone type (Type3; 8.6%) show higher precipitation occurrence probability in southern/northern and eastern MLYRB. The synoptic types of summer RPEs over MLYRB show a clear sub-seasonal variation associated with the development of East Asian summer monsoon, with Type1, Type2, and Type3 concentratively occurring in June to early July (78%), late June to July (62%) and late July to August (81%), respectively. Meanwhile, the diurnal variation of RPE precipitation amount under the synoptic Type1 and Type2 (Type3) exhibits a predominant morning (afternoon) peak. Meanwhile, the increasing trend of total RPE rainfall during 1980–1999 (2000–2022) is mainly contributed by the RPEs under Type1 (Type1 and Type2 together). The reduced coverage rate and the occurrence hours of RPEs under the monsoonal synoptic types dominate the weakened diurnal variation of the RPE precipitation amount during 2000–2022 compared with 1980–1999. This study provides a new scientific reference for the differences in the characteristics of summer RPEs in the MLYRB under different synoptic types.