Characteristics of Extreme Daily Precipitation Events in the Hydropower Basin of Chongqing (1981–2023) during the Autumn Rainy Season

Abstract This study analyzes the characteristics of extreme daily precipitation events in the hydropower basin of Chongqing from 1981 to 2023, using precipitation data from 115 meteorological observation stations and ERA5 reanalysis data. Through methods such as the empirical orthogonal function (EOF) decomposition and composite analysis, the study further investigates the atmospheric circulation drivers of extreme daily precipitation events with different spatial distribution patterns. The results indicate that over the past 43 years, 45 extreme daily precipitation events have occurred, predominantly between late August and mid-September. Notably, the frequency of these events has increased significantly since the beginning of the twenty-first century. The spatial distribution of precipitation during these events typically exhibits a north–south dichotomy within the basin, allowing classification into northern and southern types of extreme daily precipitation events. The primary atmospheric circulation drivers for the northern type include a northward shift of the 200-hPa upper-level jet stream, a west-northwestward extension of the 500-hPa subtropical high, northward vertical ascent, northward upper-level divergence, northward moisture transport, and an enhanced atmospheric apparent heat source primarily due to latent heat release from water vapor condensation. In contrast, the southern type is primarily driven by a stronger 200-hPa upper-level jet stream, a westward extension of the 500-hPa subtropical high, southward vertical ascent, southward upper-level divergence, southward moisture transport, and an enhanced atmospheric apparent heat source due to not only latent heat release from water vapor condensation but also radiative heating, surface sensible heat, and latent heat transport.