Flood risk in historic built environments: how do safe human behaviours matter?

Historic Built Environments (HBEs) in riverine contexts are flood-prone scenarios due to risk factors such as narrow and compact configurations of squares and streets, closeness to sources of risk, relevant population density, and possible presence of tourists (unaware of built environment and emergency planning). Differences in urban layout and behavioral responses of exposed users could significantly influence flood risk levels. This study investigates the impact of proper (safe) users’ emergency evacuation behaviors on flood risk assessments in different HBE layouts. Two evacuation strategies are tested (“leaving HBE” and “sheltering-in-place”) in six different parametric scenarios traced according to recurring conditions in Italian HBEs. The risk is measured through a risk index which includes hydrodynamic effects and evacuation outputs. Results show that flood risk can be lowered by adopting safe behavioral responses. Shelter-in-place resulted in the most effective strategy as it lowers the risk by up to about 35%. Such an approach not only eases holistic assessments and comparisons between different scenarios (thus highlighting which HBE layout characteristics most impact the risk, such as the square position and dimension), but it also allows evaluating the impact of users’ behaviors on risk and thus how emergency management strategies can contribute to risk mitigation.