Increasing urban flash flood risk attributable to both climate and development

Abstract

Urban flooding is one of the most damaging impacts of climate change. The two main causes of changes in rainfall‐driven flooding are altered precipitation and changes in urbanisation. Yet attribution studies only focus on the former. Furthermore, very few event attribution studies examine subdaily rainfall extremes, the timescale at which such extremes are accelerating the most. Here, for the first time, we carry out an impact event attribution study examining the effects of both climate change and urbanisation on a flash‐flooding event in the U.K. city of Leeds. By combining a convection‐permitting climate model with a flood inundation model, we show that the extent of flooding in the urban area of Leeds was increased during this event in 2014 by 49% compared to the potential flooding that would have occurred if a similar rainfall event had taken place 30 years earlier. The increase from urbanisation (29%) is almost twice that from climate change (16%). Both factors combine nonlinearly to increase flood extent by more than the sum of their parts. Our results also show that urban flood risk could be significantly misrepresented if changes in rainfall intensity are used as a proxy for changes in pluvial flooding.