A nation-wide classification of the Italian Railway Network susceptibility to flood hazard

Floods pose significant threats to railway infrastructure, given their linear extension across diverse landscapes and frequent intersections with rivers. While European countries have developed Flood Risk Management Plans (FRMPs) following the EU Floods Directive, a comprehensive analysis of railway network flood susceptibility at national scale is still lacking for Italy. Here we develop a comprehensive flood hazard classification for the Italian Railway Network (IRN). Our methodology integrates flood hazard maps, railway infrastructure data, and digital elevation models to characterize flood hazard classes along flood-prone railway routes. The approach distinguishes between steep rapid, rapid and slow flood processes, based on topographical characteristics. Results demonstrate that, for the low probability flood hazard scenario (return period ≥500 years), 25.63 % of the IRN (4,523.4 km) exhibits flood susceptibility, with this proportion declining to 19.09 % and 9.77 % for medium and high flood hazard, respectively. By performing a regional analysis across seven hydrographic districts in Italy, a substantial spatial variability emerges, with the Po River district encompassing nearly half (47.5 %) of all flood-prone railway sections. Our analysis reveals also a marked predominance of rapid flood processes, characterized by values for the time of concentration <12 h. Our classification framework provides crucial insights for risk mitigation and resource allocation, relying exclusively on FRMPs and digital elevation models. The methodology presents a scalable approach applicable to other transportation networks and study areas, supporting infrastructure managers in developing targeted flood protection measures.