Will river floods ‘tip’ European road networks? A robustness assessment

River flooding is a profound climate hazard in Europe and a threat to its road transport infrastructure. However, its impact on road network interruptions is mostly unexplored, while some have suggested that national road networks may experience tipping points. This study assesses the robustness of road networks of European countries and their potential for a tipping point: an abrupt and disproportionally large loss of network functionality, due to unfavourable combinations of floods. Methodologically inspired by percolation analysis, ten-thousands of flood combinations are sampled and their impacts on road network performance are assessed. The results show that Albania, Croatia, Serbia and Austria are relatively vulnerable, whereas Belgium, Estonia, Lithuania and Portugal are relatively robust. Tipping points in the sense of nationwide network fragmentation seem unlikely, but regional-scale tipping points can happen. Flood-proofing the identified weak spots could result in quick wins for national road operators.