Two sides of the same coin? Hydrometeorological uncertainties in impact-based flood warning systems and climate change sensitivity of floodplains

The sensitivity of floodplains to floods of various magnitudes is strongly influenced by the relationship between hydrogeomorphology and the built environment. To provide a nuanced measure of impact sensitivity to changes in flood magnitude, we introduce a novel floodplain sensitivity index (FSI) that integrates slope and curvature metrics derived from the magnitude–impact curve. We apply the method to 179 floodplains in Switzerland. Our analysis reveals that higher flood magnitudes might substantially amplify impacts, given that many of the most sensitive magnitude thresholds have not yet been exceeded. We did not find coherent patterns in the FSI across geographic or topographic regions or along entire rivers. The shape of the impact curves and thus the impact sensitivity is specific not only to the floodplain but also to the type of impact. The FSI contributes to flood risk management by providing a method to identify critical flood magnitude thresholds that lead to severe impacts if exceeded. The FSI helps in assessing the effects of uncertainties in hydrometeorological forecasts on impact-based warnings and of uncertainties in climate change projections for long-term flood risk management strategies.