Urbanization Exacerbated Rainfall Over European Suburbs Under a Warming Climate

• Published in: Geophysical research letters 2021-11, Vol.48 (21), p.n/a
• Main Authors: Yang, Long, Ni, Guangheng, Tian, Fuqiang, Niyogi, Dev
• Format: Article
• Language: English
• Subjects: climate change; Europe; extreme rainfall; urbanization
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL095987

The impacts of cities and climate warming on extreme rainfall under strong synoptic conditions are not well understood. Here, we carry out the first model‐based assessment of urban impacts on extreme flood‐producing storms for the European region. We identify contrasting roles of cities and climate warming in determining the space‐time variability of the July 14, 2021 storm over western Europe. While climate warming dominates the temporal rainfall variability over the domain, cities further enhance total rainfall over their suburbs by dynamically modifying the intensity and position of moisture convergence. There is a cyclonic structure of flow anomalies around the city induced by urban surface roughness. The rainfall anomaly induced by the interactive impacts of cities and climate warming is 50% larger than by those urban impacts alone. We highlight a need to develop a regional framework by reconciling the emerging urban‐rural contrasts in vulnerability and preparedness to hydrometeorological extremes. Plain Language Summary Western Europe experienced catastrophic extreme rainfall and flooding during mid‐July 2021 with >200 fatalities, making it one of the deadliest floods in European history. Based on high‐resolution weather simulations, we show urbanization plays an important role in enhancing rainfall and flood hazards for this storm over the suburbs of the Rotterdam‐Brussels‐Cologne metropolitan region. The rainfall anomalies are a result of both dynamical and thermo‐dynamical feedbacks from urban roughness, heat, and the mesoscale convergence. We show that the impact of urbanization on rainfall is different from that of global warming, with the latter mainly influencing the temporal variability of rainfall over the entire domain. Urban‐induced rainfall anomalies are more pronounced under a warmer climate compared to the pre‐industrial climate conditions. This is the first model‐based study to show strong urban signatures in extreme rainfall for the European region. The role of cities has not been adequately considered in the attribution analysis of weather extremes. Future adaptation and mitigation strategies to climate change need to consider the emerging urban‐rural contrasts in the exposure and vulnerability of hydrometeorological extremes. Key Points We present the first model‐based assessment of urban impacts on extreme rainfall for the European region Climate change dominates temporal rainfall variability over the entire domain, while cities en