Planning Nature Based Solutions against urban pluvial flooding in heritage cities: A spatial multi criteria approach for the city of Florence (Italy)

Aiming at defining a nature-based strategy to mitigate pluvial flood risk, a two-tiered methodology is proposed. Firstly, the areas prone to pluvial flood are identified by a spatial multi-criteria analysis that combines five criteria (imperviousness, slope, hydrologic soil groups, density of sewer system and social vulnerability) to build a Pluvial Flood Index (PFI). The PFI is validated by the comparison with historical pluvial flood events in the city and it is used for the identification of high priority areas for intervention. Then, this information is merged with the analysis of urban planning and NBS design constraints to identify the suitable areas for NBS installation. Results allow the definition of a NBS implementation strategy against pluvial flooding in the city of Florence, identifying for each pluvial flood hotspot the set of measures that can be implemented to solve the problem. The proposed approach represents a flexible assessment technique that can be reproduced in other urban context and provide useful support for NBS adoption in urban flood risk management for heritage cities.