Spatial Structure and Lifecycle Variability of Compound Dry-Hot and Heavy Rainfall Events Over the North China Plain

Abstract

Spatially compound dry-hot and heavy rainfall events expose neighboring areas to simultaneous water and heat hazards, but regional averages obscure how their components are arranged and evolve. This limits identification of recurrent event structures and the conditions associated with them. We developed an object-based framework to detect and track paired dry-hot and heavy rainfall patches over the North China Plain during May–October 1979–2025. Displacement-based criteria classified spatial arrangement, whereas K-means summarized lifecycle and geometry descriptors into organization regimes. Among 182 events, 121 (66.5%) were meridional dipoles, including 103 wet-north/dry-south cases. The organization analysis identified 87 pulse-active and 95 persistent-migratory events. Persistent-migratory events lasted longer, migrated farther, and maintained stronger 850 hPa meridional moisture transport after onset (q adjusted for the false discovery rate = 0.011). Independent gridded products reproduced anomalies averaged over the domain (r = 0.695–0.953), although patch outlines agreed less closely. Temporally blocked antecedent models discriminated organization regime only weakly (balanced accuracy 0.542; Brier skill −0.407). Under fixed 1979–2010 thresholds, event frequency increased by 133.3% from 1979 to 2001 to 2002–2025. The catalog therefore reveals recurrent spatial and lifecycle structures, but event structure carries only a weak transferable antecedent signal. Its rising frequency broadens the range of configurations that regional risk management must accommodate.