Modest flooding can trigger catastrophic road network collapse due to compound failure

Compound failures occur when urban flooding coincides with traffic congestion, and their impact on transportation network connectivity is poorly understood. Prior studies have typically considered either three-dimensional road network structure or traffic on roads, but not both, and there is a lack of network science frameworks for compound failures in infrastructure networks. Here we present a network-theory-based framework that considers compound structural, functional, and topological failures. Using high-resolution traffic data and percolation theory, we analyze the response of the Harris County, Texas (USA) transportation network to Hurricane Harvey (2017). We find that 2.2% flood-induced compound failure can reduce the size of the largest connected cluster by up to 17.7%. The results show that indirect effects, such as traffic pattern changes, must be accounted for when assessing flooding impacts on transportation network connectivity and functioning.