Failure mode and effects analysis as a screening tool for urban drainage systems failures: A comparison with hydrodynamic modelling in Feldbach, Austria

Study region The case study is the small city of Feldbach, Austria, a semi-urban catchment recently affected by flooding. Study focus Malfunctions in urban drainage infrastructure significantly increase flood risk, however resource-constrained municipalities often lack the means for complex hydraulic analysis. This study assesses the consistency of an adapted Failure Mode and Effects Analysis (FMEA), a qualitative, expert-driven tool, by comparing its severity ratings against outputs from a coupled 1D-2D hydrodynamic model. The comparison is limited to environmental and neighbouring system severity dimensions, as occurrence, detectability, and infrastructure-level severity lie outside the scope of model-based assessment. We analysed 25 failure scenarios across both centralized (grey) and decentralized (blue-green) infrastructure to assess whether expert-based FMEA severity ratings are consistent with quantitative model outputs for a range of failure types. New hydrological insights for the region Results indicate that failures in centralized "grey" infrastructure cause substantially greater system-wide impacts than malfunctions in decentralized elements within this catchment, a finding that reflects the grey-dominated structure of Feldbach. FMEA severity ratings show strong consistency with quantitative model outputs for high- and low-severity failures, though divergence remain at mid-range severity. These findings support the use of FMEA as a practical first-stage screening tool for small municipalities. We propose a tiered management strategy: utilizing FMEA for broad screening and reserving resource-intensive hydrodynamic modelling for the in-depth analysis of critical infrastructure failures.