Flood evacuation models: A simplified probabilistic approach with application to a case study in Rome

Flood events clearly induce significant impacts in urbanised regions. Over the last decades, advances in computational capacity, high-resolution digital elevation data, and open-access geospatial datasets have enabled the development of Evacuation Models (EM). However, many EMs are often not so suitable for operational use by civil protection authorities, due to their significant data requirements, high computational burden and complex parametrisation. In this context, this work aims to bridge this gap by proposing a screening-level, operational tool based on a simplified probabilistic methodology, that integrates pedestrian movement under uncertainty with a streamlined representation of flood arrival time, and then produces evacuation-time distributions and spatially explicit estimates of floodwater-pedestrian interaction probability. The approach is applied to a flood-prone urban area in Rome (Italy). Results highlight the role of network topology, route branching and behavioural variability in determining evacuation performance, revealing critical areas where existing Evacuation Plans (EPs) may require revision. Finally, we state the need for integrating simplified evacuation models into emergent decision-support frameworks, including Digital Twins for urban flood management.