Leaving or Sheltering? a Simulation-Based Comparison of Flood Evacuation Strategies in Urban Built Environments

When sudden-onset disasters occur in the urban Built Environment (BE), people must quickly leave the dangerous areas to reach safety. Floods in urban BEs surely represent a critical emergency, especially considering users who cannot evacuate upstairs, such as those placed outdoor. Management strategies focused on the evacuation planning could increase the users’ safety in a flexible but effective manner. This study compares two evacuation strategies in typological BEs through a simulation-based methodology based on the evacuation process analysis. The first strategy considers that users leave the BE, thus moving away from the source of danger flood. The second strategy adopts gathering areas positioned where the risk is lower, thus sheltering-in-place for the BE users. These strategies are tested considering fluvial flood conditions in four typological BEs, characterized by different layout in terms of streets and squares positions. The simulation-based methodology represents pedestrian evacuation under the two considered strategies depending on the hydrodynamic conditions of the BEs. Comparisons between evacuation time, flows, path length and the users’ risk depending on floodwater conditions (in terms of depth and speed) are provided. Results show that sheltering strategies can increase the users’ safety in each typological BEs, and mainly in case of the proximity between the square and the river. For instance, the users’ risk is generally reduced up to − 70%. These findings suggest that effective interventions should be designed to support the users toward “sheltering” areas, by increasing they awareness on the evacuation plan, and implementing wayfinding signs and raised platforms in the BE.