Circulation Patterns and Dynamic Drivers of Persistent Severe Rainfall over South China and the Middle-Lower Yangtze River Basin during 2012 to 2021

Persistent severe rainfall (PSR) events, defined as regional-scale rainfall processes with daily precipitation no less than 50 mm for at least three consecutive days, frequently occur over South China (SC) and the Middle-Lower Yangtze River Basin (MLYRB), with distinct dynamic mechanisms and moisture conditions in the two regions. Based on daily precipitation observations from China’s national meteorological stations and ERA5 reanalysis during 2012-2021, this study investigates the spatiotemporal distribution of PSR events in SC and MLYRB and their associated three-dimensional circulation dynamics. The analysis integrates diagnostics of 200 hPa Wave Activity Flux (WAF), perturbation streamfunction, 500 hPa geopotential height, 850 hPa wind fields, and Integrated Water Vapor Transport (IVT). Results show that PSR events in SC mainly occur during May-June, with rainfall centers over coastal and central Guangdong and Guangxi. In contrast, MLYRB events peak during June-July, with a banded rainfall pattern along the middle-lower Yangtze River. Dynamical diagnostics indicate that in SC, sustained northwest-southeast propagation of 200 hPa disturbances, the southward shift of the 500 hPa trough, and steady subtropical high maintenance provide continuous dynamical support. Concurrently, strong and persistent 850 hPa southwesterlies and long-lasting moisture transport form favorable moisture conditions. In contrast, MLYRB events are marked by rapid phase transitions of 200 hPa streamfunction anomalies and northward-westward expansion of the 500 hPa subtropical high, triggering intense rainfall development. Simultaneously, abrupt enhancement of 850 hPa southwesterlies and rapid formation of a southwest moisture corridor ensure abundant and timely moisture supply, facilitating PSR onset.