Urban areas are increasingly facing economic and human costs due to extreme precipitation and flooding. Factors such as climate change and urban expansion intensify these risks. This paper delves into a quantitative comparison of how climate change and urban development patterns expose four European cities to pluvial flooding. We aim to understand if different geographical locations and flood severities are equally influenced by urban land cover changes and climate change.
Our study focuses on Odense, Vienna, Strasbourg, and Nice, chosen for their diverse climates, urban development histories, and topographical features. We employed a combined approach using remote sensing and flood modeling to simulate pluvial flood extent. This was done for historical (1984) and present-day (2014) urban land cover, and under two climate change scenarios (RCP 4.5 and RCP 8.5). Urban land cover changes were assessed using Landsat satellite imagery from 1984 to 2014. We then integrated this data with regional climate projections of extreme precipitation to conduct 2-D overland flow simulations and flood hazard assessments.
By examining flood variations across different simulations, we quantified the individual and combined impacts of urban development and climate change, including associated uncertainties. We also considered two scenarios for urban drainage system capacity: a stationary approach reflecting present-day design, and an evolutionary approach adapting to increased imperviousness and precipitation intensities due to urban development and climate change.
Our findings indicate that all four cities experienced increased flood exposure due to a 7–12% absolute growth in impervious surfaces over the past 30 years. Climate change also exacerbated pluvial flood exposure under both RCP 4.5 and RCP 8.5 scenarios. However, the relative significance of urban development versus climate change varied significantly among cities. In Odense, urban development impacts were similar to those of climate change under RCP 8.5 (2081–2100). For Vienna and Strasbourg, urban development impacts were comparable to an RCP 4.5 scenario. Notably, in Nice, climate change emerged as the dominant driver of increased flood exposure, overshadowing urban development.
This geographical variation stems from differences in soil infiltration, historical urban development trends, and regionally specific climate change projections affecting extreme precipitation. We found that upgrading urban drainage systems in response to urban development effectively mitigates increased runoff from sealed surfaces. However, adapting drainage systems solely to climate change-induced precipitation intensity increases only marginally reduces flooding during the most extreme events.
In conclusion, while both urban development and climate change intensify pluvial flood risks across European cities, their relative impacts differ significantly based on regional climate characteristics and urban growth patterns. Cities like Nice, experiencing more pronounced climate change impacts on precipitation, need to prioritize climate adaptation strategies. Conversely, cities like Odense, Vienna, and Strasbourg must address both urban development and climate change to effectively manage increasing flood exposure. Investing in adaptive urban drainage systems is crucial, especially considering the projected increases in extreme precipitation due to ongoing climate change.
