How and why has extreme hourly precipitation changed in the major urban agglomerations over China?

Understanding changes in sub-daily precipitation extremes and its attribution is critical for urban planners to build more sustainable and reliant cities. Three major urban agglomerations have been formed in China as a result from fast economic development since about the early-1990s, namely, the Pearl River Delta (PRD) in coastal South China, the Yangtze River Delta (YRD) in coastal East China, and the Beijing-Tianjin-Hebei (BTH) region in northern China. In this study, the hourly precipitation data in 1971-2018 from national weather stations are combined with historical land-use change data to investigate changes in extreme hourly precipitation (EXHP) in the three regions. Also, a large ensemble of extreme rainfall events (EXREs) during 2011-18 are analyzed using observations collected by densely-distributed automatic weather stations and radar network combined with reanalysis data. The results suggest that the strong urban heat island (UHI) effect in these urban agglomerations is conducive to intensification of hourly precipitation. However, statistically insignificant changes in EXHP are observed over the BTH region. In contrast, significantly increasing frequency of EXHP occur over the other two coastal urbanized regions, with some distinct features in the evolution of EXHP-producing storms and the relevant synoptic situations between the two regions. The individual and combined effects of land-cover and land-use (LCLU) change and increasing anthropogenic aerosol emission are investigated by use of an integrated modeling approach. An ensemble of convection-permitting simulations is performed, combining two LCLU and aerosol emission scenarios. The influences of these two factors are discussed based on the simulations.