Flood-sensitive land take (FSL) analysis: A new way to read how urban sealing shapes flood risk

Urban flooding is an increasing environmental hazard. It is intensified by land take and the conversion of natural landscapes into sealed urban surfaces. These changes reduce stormwater management capacity. The hydrological processes driving flooding are well understood. However, the impact of land-use transitions on flood sensitivity is less explored, especially in different urban contexts and integrating land take into flood risk management remains a major challenge. In response to this gap, this study analyses land use changes in Gdańsk (Poland), Milan (Italy), Ghent (Belgium), and Oslo (Norway) between 2012 and 2018. It examines their relationship with urban water accumulation using the InVEST Urban Stormwater Retention Model. The study introduces the Water Accumulation Sensitivity Index (WASI) and the Normalised Water Accumulation Sensitivity Index (NWASI), which provide a quantitative framework for assessing urban sensitivity to water accumulation. The findings show how local land take patterns influence flood risk. Comparative results show that Gdańsk and Milan exhibit increased accumulated water linked to conventional residential and industrial expansion. Oslo displays high hydrological sensitivity despite minimal land take, due to forest and agricultural conversions. Ghent demonstrates that land take directed toward green infrastructure can stabilize or even reduce water accumulation. WASI and NWASI enable managers to identify high-risk areas for targeted interventions, such as green infrastructure related measures or restrictions on impervious surface development. This research supports evidence-based land use policies to balance urban growth with flood resilience and to improve environmental management and climate adaptation.