An innovative approach to assess the impact of urban flooding: Modeling transportation system failure due to urban flooding

The transportation system is often considered a critical infrastructure as the failure of its components can have a substantial impact on the economy and social well-being of a country. Extreme weather events such as urban flooding disrupt transportation networks with delays, diversions, and partial or full closure of roads and, thereby, influence human movement patterns. Most studies in the field of transportation network failure due to urban flooding are focused only on micro-scale, in-situ approaches rather than referring to the holistic impact on the entire transportation system. Moreover, such approaches are failed to address the changes in travel behaviour concerning their trip purpose, mode choice, and income which can be changed due to inundation. Hence, this study presents a novel approach to assess the entire transportation system failure due to urban flooding. Consequently, the impact of urban flooding on human movement patterns was assessed. The proposed framework is developed based on the network centrality measures, namely, betweenness centrality and closeness centrality. The study is predominantly based on Open-Source GIS tools and the case study is carried out in Colombo, Sri Lanka which has the highest concentration of population and transportation network. The hotspots of the failure of the network were statistically and spatially illustrated. The study revealed three key findings; (a) the fragmented network due to inundated road segments triggers the spatial changes in the accessibility, particularly decreasing the accessibility in most of the core areas whereas increasing the accessibility in some peripheral areas which are not significant under the baseline condition (2) the functional changes of the entire transport network occurs due to flooding events (3) the considerable changes in the trip length occurs due to the disruption of transport network links and the impact is mostly notable in long-distance trips compared to short distance trips. The proposed framework can be utilized as a planning tool for both disaster practitioners and infrastructure operators in identifying the flood risk; and prioritizing flood mitigation investments, thereby, making the transportation system more robust to extreme flooding.