Effects of urbanization on short-duration and long-duration intense rainfall across China's three major urban agglomerations

Under the combined influences of climate change and urbanization, rainfall patterns in densely populated megacity clusters have experienced significant changes. However, the impacts of urbanization on rainfall patterns, particularly across regions with distinct climatic and geographic contexts, are still poorly understood. In this study, we focused on China's three major urban agglomerations (Pearl River Delta, Yangtze River Delta, and Beijing-Tianjin-Hebei) and systematically analyzed the effects of urbanization on short-duration intense rainfall (SDIR) and long-duration intense rainfall (LDIR) using high-resolution precipitation data, revealing distinct regional divergence patterns. The results demonstrate that urbanization most significantly intensifies SDIR, with marked regional heterogeneity. SDIR hotspots are concentrated in urban cores within the YRD and PRD regions. However, in the BTH region, topographic disturbances and urban moisture suppression shift the SDIR hotspots toward piedmont transition zones. Diurnal SDIR variations are regulated by local circulations and hydrothermal conditions; nocturnal urban heat islands combined with mountain-valley circulations enhance nighttime SDIR events in the BTH, while afternoon sea breezes with moisture transport and high convective potential dominate SDIR frequency in the PRD and YRD. For LDIR, nocturnal monsoon intensification and topographic effects drive high coastal occurrence in the BTH and PRD, whereas the topographically homogeneous YRD exhibits LDIR hotspots linearly aligned with the Yangtze River and urban areas during both day and night, potentially linked to elevated convective available potential energy.