Impacts of Urbanization on Precipitation of Mega-cities in the Northern Hemisphere

Urbanization significantly alters land surface characteristics, thereby influencing precipitation patterns. However, whether urbanization leads to urban wet islands or dry islands remains controversial. Here, we assess the sensitivity of precipitation to urbanization, defined as the slope of the regression between precipitation and the proportion of impervious area at each site or grid within a city, for 290 mega-cities in China, 51 in Europe, and 108 in the United States, using in situ datasets and two satellite-based products (MSWEP and GPM). Our results show that 46–70% of Chinese, 39–78% of European, and 37–71% of US cities exhibit negative sensitivity, depending precipitation product used, which highlights the uncertainties in precipitation products. We further examine how urbanization influences the frequency and intensity of heavy and light rainfall events, and find that it tends to enhance heavy rainfall and reduce light rainfall. Consequently, the reduction in light rainfall predominantly drives the negative sensitivity of annual precipitation to urbanization. Our study reveals the complexity of urban precipitation dynamics, and underscores the need for high-resolution and accurate datasets to better quantify urbanization impacts on hydrological processes.