Under global warming, projected changes in precipitation have shown an asymmetrical shift from light to heavy precipitation (HP) over China. Meanwhile, HP events can be preceded by moist heatwaves (HWs; i.e., hot and humid weather). However, the role of urbanization in this shift and the effect of moist HWs on increasing urban HP remains unknown. Based on statistical analyses of daily weather observations and ERA5 reanalysis data, we show that increases in total rainy-season (May-September) precipitation over the Yangtze River Delta (YRD) urban agglomeration of East China are characterized by decreasing light precipitation and increasing heavy precipitation during 1961–2019. This asymmetrical shift toward heavier precipitation is even more prominent in urban than rural areas. Areas with faster urban expansion rates exhibit stronger negative (positive) trends in light (heavy) precipitation. Furthermore, we divide summer HP events into NoHW- and HW-preceded events in the YRD urban agglomeration of China. During the period 1961–2019, the YRD has experienced more frequent, longer-lasting, and stronger intense HP events in the summer season (i.e., June–August), and urbanization has contributed to these increases. In contrast, urban effects on HP are almost absent if we remove HW-preceded HP events from all HP events. Urbanization-induced increases in HP are associated with, and magnified by, moist HWs in urban areas of the YRD region.
 

urbanization, heatwaves, heavy precipitation