Optimizing Shelters and Evacuation Paths Against Flood in Historic Urban Built Environments

When floods occur, pedestrians may be forced to evacuate the risk areas, and the presence of emergency plans is fundamental to reduce fatalities. Historic Urban Built Environments (HUBEs) in flood-prone territories are critical scenarios because of complex and compact layouts, poor implementation of risk-mitigation strategies, and attractiveness for tourists unfamiliar with the spaces. This work provides a novel risk-based methodology to determine the optimal evacuation solution by varying the approach for the path choice, and the number of available shelters in the HUBE. First, an Integer Linear Program is defined to consider different pedestrians’ approaches to the path choice (i.e.: minimizing the path length, time, effort). Then, to select the best overall evacuation solution, a synthetic Risk Index RI is developed based on Key Performance Indicators that jointly consider aspects concerning the urban layout, the event intensity, and the human motion. The application scenario is a typological HUBE with narrow streets perpendicular to each other and a square close to a river, and the pedestrians’ motion conditions depend on the hydrodynamic conditions generated by a real-world flood within the HUBE. Results identify the minimum number of shelters to guarantee the minimum RI, the optimal shelter positions depending on the path choice approach, and the best evacuation paths from each position of the HUBE. Results offer first insights on where/how to install wayfinding systems and urban furniture and could represent a first step toward the development of tools for the communication of real-time risk update.