The Impact of Urban Heat Island on Extreme Rainfall Events in Presummer Over the Pearl River Delta Metropolitan Region Under Different Synoptic Systems

Urban heat island (UHI) effects significantly influence regional extreme rainfall. However, their varying impacts on presummer extreme rainfall events (EREs) under different synoptic systems in the Pearl River Delta (PRD) metropolitan region remain inadequately understood. Based on rain gauge observations from 2008 to 2021 and the K‐means clustering algorithm, this study aims to clarify how UHI effects influence the spatial distribution and diurnal variation of presummer EREs in the PRD across three dominant synoptic categories: Warm‐Sector (WS), Front/Shear Line (FS), and Cyclonic‐Anomaly (CA) systems. The results demonstrate that the association between UHI and EREs varies according to differing synoptic conditions. For WS EREs, strong UHI is accompanied by a shift in peak rainfall intensity from the early morning to the afternoon. The intensified precipitation is concentrated in the northern Pearl River Estuary during the afternoon coinciding with the accumulation of thermal energy that favours the development of local circulation. Regarding FS EREs, strong UHI conditions are associated with a northward retreat of the front and intensified sea breezes in the afternoon, with precipitation primarily concentrated over inland urban and downwind areas within the PRD region. In contrast, CA EREs, which are primarily influenced by cyclonic circulation, exhibit a reversed diurnal rainfall pattern under strong UHI conditions, with rainfall intensification occurring in coastal areas during the morning. This study provides observational evidence to enhance fine‐scale predictions of urban extreme rainfall and offers practical insights for urban flood risk mitigation and regional meteorological disaster prevention. Notably, these correlational results are physically plausible. However, further numerical sensitivity experiments are necessary to explicitly validate the proposed UHI‐driven mechanisms.