Flood risk to cultural heritage: a voyage through scales

Floods are among the most frequent and damaging events worldwide, affecting population and residence buildings, economic activities, agriculture but also cultural heritage (hereinafter CH). Flood impacts to CH are very challenging to evaluate, due to their intangible values (e.g., spiritual, social, aesthetic) and difficulty in replacing unique objects. These aspects make the evaluation of CH exposure and vulnerability complex, also depending on the scale of analysis adopted. This work aims at illustrating the differences in risk evaluations, as the scale of analysis varies. It highlights the information usually available for flood risk analysis of CH when moving from a large scale, e.g. regional/national level, to building scale, with different stakeholders perspectives, and demonstrates a very detailed approach for hazard modelling inside the CH building. The regional/national scale considers CH often as a point feature and usually aims at identifying geographic damage hotspots, i.e., river basin authority perspective. Few information is available at this scale, mostly hazard classification (low to high probability of occurrence) and often a tailored taxonomy for exposed assets has to be developed. The site/city scale usually considers cultural heritage as a polygon feature with a better description of flood depths and of building characteristics such as the building type (e.g., religious or rural), the presence of underground floors or the presence of artworks. It identifies risk priorities and potential damage, i.e. it adopts a mayors perspective. The building scale analysis, i.e., heritage manager perspective, requires moving towards a 3D geometric description of the cultural building by incorporating elevations of features with respect to the terrain to better understand actual inundation depths and their effects. On-site inspections are required to measure specific characteristics of the structure such as the location and the height of the openings, which let floodwater enter inside the building. Such information allows for a downscaling of a city inundation model, that provides the hydrograph to assign as boundary condition to the building. The method is applied to the Florence area (central Italy) and to a museum inside the city center. The 2D inundation model at building scale shows the inundation inside the basement of the museum, formerly a crypt, where a part of the permanent art collection is exhibited. The museum model reveals the flow and the quantity of water within different part of the building. A comparison with the historical records of the 1966 flood in the Museum, confirms the findings of the simulation. Acknowledgments. This work received co-funding by (i) Regione Toscana, Fondo per lo Sviluppo e la Coesione 2014-2020, Project GiovaniS and by (ii) the RETURN Extended Partnership, European Union Next-GenerationEU (National Recovery and Resilience Plan NRRP, Mission 4, Component 2, Investment 1.3 D.D. 1243 2/8/2022, PE0000005)