Urbanization and Climate Change Impacts on Rainfall: A Numerical Sensitivity Study over Milan

Over the past decades, urbanization has surged globally, with more than 50% of the population now residing in cities. Projections indicate a continued increase in urban populations, accompanied by significant changes in land use and land cover. These alterations are expected to affect the temporal and spatial distribution of precipitation. Combined with the effects of climate change, which is likely to increase the frequency and intensity of short-duration heavy rainfall, the risk of flooding in urban environments is expected to rise. Understanding the combined impacts of urbanization and climate change on rainfall dynamics is therefore critical for effective flood risk management and urban planning. 
In this study, we investigate the influence of urbanization and climate change on short-duration rainfall events in Milan. We used the Weather Research and Forecasting (WRF) model to simulate 8 rainfall events in the current urban setup and climate, and to assess how these events will alter in different scenarios of urbanization and climate change. Results reveal that the impact of global warming on rainfall space-time characteristics is stronger than that of urbanization. However, urbanization significantly contributes to the urban heat island effect, which, when combined with global warming, amplifies its influence on rainfall patterns. These findings underscore the importance of accounting for the combined impacts of climate change and urbanization in studies of future rainfall patterns, particularly for flood risk assessments and urban resilience planning.