Considerable increase in sub-daily precipitation extremes and its possible causes across the middle‒lower reaches of Yangtze River

To address the gaps in understanding the spatiotemporal changes of sub-daily precipitation extremes (SPEs) across different timescales and the quantitative role of urbanization, the study takes the Middle‒Lower Yangtze River (MLYR) as a case study region to quantify changes in SPEs during the summers (June–August) from 1971 to 2022 and explores the underlying mechanisms. Results indicate substantial increases of 4.3%–11.5% per decade in both the frequency and intensity of SPEs, with notably steeper upward trends observed between 2001 and 2022. The frequency of SPEs increased approximately twice as rapidly as their intensity. For shorter-duration SPEs (1–3 h), the upward rate of intensity was 12% faster and spatially 9% more extensive compared to longer-duration events (6–12 h). Rapid urbanization amplified the SPEs, contributing 8%–36% to these increases. Against the backdrop of global warming and rapid urbanization, the strengthened and westward-extended Western Pacific Subtropical High, increased saturated vapor pressure, enhanced specific humidity and moisture convergence, and upward K -index play key roles in rising SPEs, especially in urban areas. These findings provide critical insights for developing climate adaptation strategies in urbanizing regions.