Flood exposure analysis of road infrastructure - Comparison of different methods at national level

Assessing the flood exposure of infrastructure is crucial for sustainable flood risk management. We propose to define road exposure to floods as any road segment/element located within a flood hazard zone. On the example of Switzerland, we develop and compare three methods to assess the flood exposure of the road infrastructure: absolute road area potentially flooded (method A), relative road area potentially flooded (method B), and a network-based approach using the edge betweenness centrality index (method C). The results are aggregated and ranked in grid cells of 2 km by 2 km for comparison. The ranks are directly proportional to exposure levels. The results present distinct spatial patterns; grid cells with higher values in method A indicate where more road surfaces are in a flood hazard zone (urban or high road density areas in flood plains), while method B highlights where most of the road surface is in flood hazard zones of predominantly mountainous areas of Switzerland. Higher values in method C present areas where the most-connected road links within a network are exposed to floods. Most of the grid cells that have higher values in method B than in method C indicate isolated mountain valleys that can be accessed only by a single mad exposed to floods. The study demonstrates the importance of an appropriate choice of methods in flood exposure analysis. As exposure analysis is a key step in flood risk assessment, the presented results provide information essential for decision making in disaster risk reduction.