floods on mobility is more prominent and discrepant. The average share of the road network that is flooded by at least 30 cm is 3.64% (or 24.84%) under the 5-year (or 1000-year) return period–yet 11.58% (or 65.67%) of simulated trips fail in the same scenario.

Past case studies on city or regional road networks proposed a positive correlation between road network resilience and graph-theoretic metrics, such as network density. Our study at the global scale, examining a total number of 2,564 road networks shows that network density helps partially understand network resilience to floods. The degree to which the variance of network resilience can be explained by network density alone varies case by case. When combining network density with flood exposure patterns, we show an increase in the overall explainability of network resilience. Furthermore, the proportion of the variance for percentage failed routes that can be explained by flood exposure and network density increases with flood return period. Nevertheless, it should be noted that the underlying governing factors that influence network resilience are inherently complex and vary across space. In locations where the political, socioeconomic, environmental, and cultural conditions for road infrastructure development are complex, additional factors need to be taken into the equation to fully understand road network resilience to floods.

Considering the scale of this study, we made several generalizations and assumptions when modeling the impact of floods on the mobility within settlement clusters. Due to limitations in data availability, we are unable to fully consider traffic congestion, local travel behavior patterns, or road conditions in the disruption simulation process. In addition, the exclusion of tertiary and residential road networks is able to reduce but not exclude selection bias that stems from the incompleteness of the OSM data set at the global scale. In locations where primary and secondary road network data is incomplete, our approach will likely overestimate the adverse impact of flood hazard on mobility.

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