Building-scale flood loss estimation through vulnerability pattern characterization: application to an urban flood in Milan, Italy

The vulnerability of flood-prone areas is deter- mined by the susceptibility of the exposed assets to the haz- ard. It is a crucial component in risk assessment studies, both for climate change adaptation and disaster risk reduc- tion. In this study, we analyse patterns of vulnerability for the residential sector in a frequently hit urban area of Milan, Italy. The conceptual foundation for a quantitative assess- ment of the structural dimensions of vulnerability is based on the modified source–pathway–receptor–consequence model. This conceptual model is used to improve the parameteri- zation of the flood risk analysis, describing (i) hazard sce- nario definitions performed by hydraulic modelling based on past event data (source estimation) and morphological features and land-use evaluation (pathway estimation) and (ii) the exposure and vulnerability assessment which consists of recognizing elements potentially at risk (receptor estima- tion) and event losses (consequence estimation). We charac- terized flood hazard intensity on the basis of variability in water depth during a recent event and spatial exposure also as a function of a building’s surroundings and buildings’ in- trinsic characteristics as a determinant vulnerability indica- tor of the elements at risk. In this sense the use of a geo- graphic scale sufficient to depict spatial differences in vul- nerability allowed us to identify structural vulnerability pat- terns to inform depth–damage curves and calculate potential losses from mesoscale (land-use level) to microscale (build- ing level). Results produces accurate estimates of the flood characteristics, with mean error in flood depth estimation in the range 0.2–0.3 m and provide a basis to obtain site-specific damage curves and damage mapping. Findings show that the nature of flood pathways varies spatially, is influenced by landscape characteristics and alters vulnerability spatial dis- tribution and hazard propagation. At the mesoscale, the “con- tinuous urban fabric” Urban Atlas 2018 land-use class with the occurrence of at least 80 % of soil sealing shows higher absolute damage values. At microscale, evidence demon- strated that even events with moderate magnitude in terms of flood depth in a complex urbanized area may cause more damage than one would expect.