Urbanization-Induced Increases in Heavy Precipitation are Magnified by Moist Heatwaves in an Urban Agglomeration of East China

Heavy precipitation (HP) events can be preceded by moist heatwaves (HWs, L., hot and humid weather), and both can be intensified by urbanization. However, the effect of moist HW on increasing urban HP remains unknown. Baked on statistical analyses of daily weather observations and ERAS reanalysis data, we herein investigate the effect of mdist HWs on urban intensified HP by dividing summer HP events into NoHW and HW preceded events in the Yangtze River delta (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 (ie., Jung August), and urbanization has contributed to these increases (by 22.66% 37.50%). In contrast, urban effects on HP are almost absent if we remove HW preceded HP events from all HP events. Our results show that urbanization induced increases in HP are associated with, and magnified by moist HWs in urban areas of the YRD region. Moist HWs are conducive to an unstable atmosphere and stormy weather, and they also enhance urban heat island intensity, driving increases in HP over urban areas.

Automated summary

Moist heatwaves can intensify urban heavy precipitation events, especially in the Yangtze River delta region. In recent years, there has been an increase in the frequency and intensity of heavy precipitation events caused by moist heatwaves in the summer season. Urbanization has further exacerbated this trend.