How much do users matter? An integrated method for building flood vulnerability and exposure assessment in Historic Urban Areas

The definition of sustainable strategies for risk mitigation in Urban Built Environments (UBEs) prone to flooding should be based on holistic yet quick approaches that comprise hazard, physical vulnerability, and user factors. In particular, the ways users occupy, live and behave in UBEs introduce significant spatiotemporal dynamics in the final risk due to their user exposure (how many?) and vulnerability (of which type?). These effects can be relevant in Historic UBEs (HUBEs), due to building heritage features and the related need to balance mitigation strategies with conservation and preservation. Therefore, quickly applicable analyses, exploiting available databases, should be developed, and the reliability of methods that incorporate user-related, dynamic parameters should be demonstrated in comparison to established “static” analyses of hazards and physical elements. This work proposes a building-scale approach for vulnerability and exposure assessment to floods, aimed at identifying “hot-spots” in HUBEs, by combining “static” and “dynamic” assessment methods. “Static” (e.g. material degradation, construction typology, urban morphological features) and “dynamic” (e.g. daily occupancy schedules, occupant densities/typologies) are combined within a GIS database, using single and multi-factor metrics. The method is demonstrated using a relevant Italian case study. Results remark that considering user exposure and vulnerability over time introduces significant differences in flood risk metrics and HUBEs hotspots, for both public buildings, due to daytime occupancy schedules, and residential buildings, where risk levels increase up to 80%, considering the possible low physical vulnerability of these buildings. This work therefore provides robust approaches to support informed decision-making in the prioritisation of targeted mitigation strategies within HUBEs.