Overlooking probabilistic mapping renders urban flood risk management inequitable

Characterizing flood-related hazards has mostly relied on deterministic approaches or, occasionally, on particular uncertainty sources, resulting in fragmented approaches. To analyze flood hazard uncertainties, a fully integrated floodplain modeling information system has been developed. We assessed the most relevant uncertainty sources influencing the European Floods Directive’s third cycle (2022–2027) concerning extreme flood scenarios (a 500-year flood) and compared the results to a deterministic approach. Flood hazards outputs noticeably differed between probabilistic and deterministic approaches. Due to flood quantiles and floodplain roughness characterization, the flood area is highly variable and subject to substantial uncertainty, depending on the chosen approach. Model convergence required a large number of simulations, even though flow velocity and water depth did not always converge at the cell level. Our findings show that deterministic flood hazard mapping is insufficiently trustworthy for flood risk management, which has major implications for the European Floods Directive’s implementation.