Analyzing the Impact of Floods on Urban Mobility Using Mobile Phone Data: A Case Study of the Vesdre Catchment Area

In Belgium, floods are acknowledged as one of the most frequent natural disasters, posing serious threats to people's lives and property. Growing evidence suggests flood risks will intensify in the coming decades, driven by climate change, population growth, and evolving land use patterns at the catchment scale. These compounding factors make improved flood risk understanding and management an urgent priority. The impact of floods on the transportation system primarily stems from road interruptions, which significantly affect travel demand. Exploiting mobile phone data collected by providers makes it possible to geolocate mobile phone users over time to derive time-dependent crowding maps. By intersecting these maps with flood inundation data, we can quantify human exposure to flood risks. This integrated approach enables a detailed analysis of both the spatial extent of floods and temporal changes in population movement patterns during flood events. In this context, we propose a sensitivity analysis based on mobile phone data collected from pre- and post-flood calendar periods in the Vesdre catchment area (Wallonia, Belgium). In light of the floods that occurred in July 2021, mobile phone data collected in 2018 and 2022 have been processed and compared. Meanwhile, we investigate the impact of the transportation infrastructure disruptions on mobility within the Vesdre catchment area and apply a Tobit regression model to analyze the significant parameters. As a result, we observe a decrease in interaction between the valley and the plateau, except between urban centers in the valley and neighboring residential communes in the heights, along with a general decline in mobility in the most affected communes. This suggests that the flooding has incited people to get further away from the river. Besides, we find that the parameter representing the number of out-of-service transportation infrastructures per kilometer is significant in the 2022 flow regression.