How urban layout and pedestrian evacuation behaviours can influence flood risk assessment in riverine historic built environments

Riverine Historic Built Environments (HBEs) in urban centres are relevant scenarios for flood risk, due to the compact layout of their outdoor spaces, that are squares and streets, and their position in flood-prone areas. Differences in HBE layout can provide differences in flood risks, but excluding the response of exposed individuals can lead to risk underestimation or overestimation, as for other hazards. This work is a first attempt to compare how accounting or not pedestrian evacuation behaviours can affect flood risk assessment and emergency strategies evaluation. Parametric configurations of typical HBEs are provided on case-studies, and existing tools for hydrodynamic and pedestrian evacuation simulation are applied to them. Risk indexes for the whole HBE (macroscale) and each of its outdoor space (microscale) in it are provided. Results show how the risk indexes trends accounting or not pedestrian evacuation behaviours at the macroscale are similar, while differences at the microscale exist (about 15% in absolute terms). Concerning emergency strategies, sheltering seems to decrease the risk for the whole HBE up to 33% in comparison to leaving the flood-affected area. Results also support where/how to place gathering areas in the HBE.