Impacts of urbanization on extreme precipitation in the Guangdong-Hong Kong-Macau Greater Bay Area

The effect of urbanization on extreme precipitation in the Guangdong-Hong Kong-Macau Greater Bay Area (GBA), which has been undergoing dramatic urbanization, is explored in this study. Two comparative urban development scenarios (2000 and 2015) were designed to examine the sensitivity of extreme precipitation to urbanization in numerical experiments. The simulation reveals that extreme precipitation remarkably increased in the core and northeast areas of the urban agglomeration, a finding that is also verified by statistics of the secular trend of observed data. Through the classification of extreme precipitation, it was found that urbanization significantly impacts only convectional extreme precipitation, while it has little effect on frontal or typhoon extreme rainfall. Further comparative analysis of model outputs revealed that urbanization increases surface roughness, which enhances mechanical turbulence and results in stronger low-level convergence and convection enhancement. Urbanization also leads to a change in the surface energy balance. The increased sensible heat flux enhances the temperature and boundary layer circulation and transports more water vapor, mixing it into the upper atmosphere in urbanized areas and increasing the intensity and frequency of convectional extreme precipitation.