Urbanization and climate change impacts on future heavy summer rainfall in Milan, Italy

Over the past fifty years, urbanization has undergone a swift surge, with over 50% of the global population now residing in cities. A further rise in urban population in the forthcoming decades is expected based on future projections. This surge in urbanization, along with associated alterations in land use/land cover, has the potential to modify the temporal and spatial characteristics of precipitation. Additionally, the anticipated escalation in global warming is likely to amplify both the magnitude and frequency of short-duration (convective) heavy rainfall. These two factors separately have the potential to lead to an increased risk of urban flooding. Consequently, it is imperative to comprehend how urbanization and climate change together may impact short-duration heavy rainfall events - a crucial aspect for effective flood risk assessments and planning sustainable urban drainage systems. To this end, we explore the influence of climate change and urbanization on the spatiotemporal properties of rainfall. Our investigation involves the simulation of current and future scenarios of urban development and warming over Milan, utilizing the convection-permitting Weather Research and Forecasting (WRF) physically-based atmospheric model. The findings of this study underscore that future urbanization will influence the distribution of rainfall in terms of both time and space. Furthermore, the combined effects of urbanization and climate change can significantly reshape the structure of short-duration heavy precipitation events.