Tracking Flood-Inducing Rainfall in the Mid–Lower Reaches of the Yangtze River Basin, China: Climatology, Variability, and Spatial Signatures

Under the subtropical monsoon climate, summer floods in the mid–lower reaches of the Yangtze River basin (MLYRB) pose pressing challenges to flood control and disaster risk management in China. There are still gaps in understanding the climatology and variability of flood-inducing rainfall (FIR). This study proposes an identification algorithm designed to comprehensively characterize both the intensity and persistence of FIR in the MLYRB. We identified 142 FIR events between 1961 and 2020 and analyzed their variations across three dimensions: climatic patterns, temporal dynamics, and spatial signatures. The results reveal a unimodal temporal distribution of FIR events, with a distinct peak in July. Both FIR intensity and duration correlate significantly with its onset dates. The spatial dispersion of the FIR rainband exhibits greater variability than total rainfall. The spatial dynamics of the FIR centroid show a long-term trajectory: eastward migration trend from 1961 to 1984, westward retreat trend from 1985 to 2002, and resumed eastward trend since 2003. The decadal trends of FIR rainband are tightly linked to the interactions between cold vortices in mid–high latitudes and moisture transport in low latitudes, which are driven by the Indian Ocean Basin Mode and the El Niño–Southern Oscillation. The findings provide a foundation for improved regional flood prediction and disaster risk reduction.