Investigating pedestrian behavioral patterns under different floodwater conditions: A video analysis on real flood evacuations

Understanding how people behave during emergencies is fundamental to improve their safety. In the case of flood evacuation, people have to deal with built environments extremely modified by the floodwaters and that hence influences human-environment interactions both from a qualitative and quantitative standpoint. In this sense, the observation of real events is fundamental to define behavioral patterns and their relation to floodwater conditions. To this end, in this work, we analyzed 139 videotapes of recent real-world flood evacuations in outdoor Built Environments involving about 1000 people all over the World (the largest set analyzed so far). The frequencies of behavioral patterns are associated with water depth (measured with respect to ankles, knees, and waist), flow (i.e., still or flowing), and evacuation phase in which they are observed (that is before, during, and after the evacuation). Specific factors like voluntariness, human response, and presence of reference elements in the flooded built environment are also considered. Frequent by-literature behaviors have been considered, and new-noticed ones have been assessed. Results unveil that the most frequent floodwater conditions and thresholds to trigger each behavior concern waters between the ankles and the waist, thus excluding slight and extreme interactions with floodwater. The retrieved behavioral patterns could be employed to develop and validate behavioral models for flood evacuation simulators, and to create critical scenarios for people's training. Furthermore, they trace quick insights to help safety planners in the design of risk-reduction measures also considering local and/or temporary risks due to the floodwater conditions.