Modeling the effects of urbanization expansion on convective precipitation: Insights from Shanghai

With the expansion of large metropolitans and the increasing global population, there is a pressing need to have a better understanding of how cities affect extreme weather, especially heavy rainfall events that can potentially trigger urban floods. With the complex interplay and feedback between land, sea, and atmosphere, our understanding of how urbanization expansion impacts precipitation in coastal areas is limited. Here we use a high-resolution Weather Research and Forecasting (WRF) convection-permitting model to simulate 24 summer convective storms over Shanghai, China. We simulated the storms for the present urban setting and considered additional 3 urban expansion scenarios. Our results show that diverse urban-induced precipitation anomalies occur over the Shanghai metropolis due to different urban-surroundings gradients of low-level temperature and water vapor. 37.5% of storms show a constant increase in precipitation accumulation in response to urban expansion, whereas 29% have the reverse trend. The findings provide the potential mechanisms of urban rainfall modification in areas where land and water interact, offering useful insights for urban planning and flood control strategies in Shanghai, as well as other rapidly urbanizing cities.