Spatiotemporal Features and Associated Synoptic Patterns of Extremely Persistent Heavy Rainfall Over China

Extremely persistent heavy rainfall (EPHR) is characterized by high rainfall intensity and long durations, which can cause destructive natural disasters. In this study, hourly merged precipitation data for 2009-2019 are used to investigate the spatiotemporal distribution of EPHR over China. Reanalysis data are used to classify synoptic patterns related to EPHR. Observations show that the EPHR process is substantially asymmetrical, occurring mostly in South China, whereas its strongest intensity takes place in North China. There is a tendency for EPHR to occur near coastal and mountainous areas, basins, and urban agglomerations. Monthly and diurnal patterns of EPHR exhibit complex regional disparities in frequency and cumulative precipitation. EPHR exhibits a bimodal structure during summer in South and Southwest China, whereas a unimodal structure is observed in Huang-Huai valleys, and early morning peaks are substantial elsewhere. Furthermore, the synoptic patterns associated with EPHR also differ by region. Using an objective synoptic classification method, typical synoptic patterns are classified in each region. Combining the effect of land-sea contrast, the low vortices system, low-level jets (LLJs), and shear lines play a key role in supporting EPHR in South China. The location of EPHR south of the Yangtze River is substantially controlled by the intensity of southwest vortex, LLJs, and the shear line, while the southwest vortex dominates in Southwest China. The effects of the low vortex, shear lines, and terrain are prominent in Jianghuai region. Furthermore, EPHR in the northern region is closely related to western Pacific subtropic high and local vortices.