Floods often cause significant damage to transportation infrastructure such as roads, railways, and bridges. This study identifies several topographic, environmental, and hydrological factors (slope, elevation, rainfall, land use and cover, distance from rivers, geology, topographic wetness index, and drainage density) influencing the safety of the railway infrastructure and uses multi-criteria analysis (MCA) alongside an analytical hierarchy process (AHP) to produce flood susceptibility maps within a geographic information system (GIS). The proposed methodology was applied to the catchment area of a railway track in southern Italy that was heavily affected by a destructive flood that occurred in the autumn of 2015. Two susceptibility maps were obtained, one based on static geophysical factors and another including triggering rainfall (dynamic). The results showed that large portions of the railway line are in a very highly susceptible zone. The flood susceptibility maps were found to be in good agreement with the post-disaster flood-induced infrastructural damage recorded along the railway, whilst the official inundation maps from competent authorities fail to supply information about flooding occurring along secondary tributaries and from direct rainfall. The reliable identification of sites susceptible to floods and damage may provide railway and environmental authorities with useful information for preparing disaster management action plans, risk analysis, and targeted infrastructure maintenance/monitoring programs, improving the resilience capacity of the railway network. The proposed approach may offer railway authorities a cost-effective strategy for rapidly screening flood susceptibility at regional/national levels and could also be applied to other types of linear transport infrastructures.

This study explores the application of the Rain-on-Grid approach within the two-dimensional (2D) Hydrologic Engineering Center’s River Analysis System (HEC-RAS, version 6.6) for a selected area (~ 230 km²) of the Low Calore River catchment in Southern Italy, which was heavily hit by an extreme rainfall event on October 14–15, 2015. This event, lasting about 17 h, triggered a range of geo-hydraulic phenomena, including extensive flooding of the Calore River, with physical damage to the railway infrastructure. The hydrodynamic model was used to reconstruct the effects of the observed rainfall event by including relevant processes such as spatially distributed rainfall, upstream discharge input, infiltration losses, and flow propagation across hillslopes and within the Calore River. The results demonstrate that 2D Rain-on-Grid HEC-RAS simulations, which account for the minor tributary network, can reproduce realistic correlations with recorded damage to linear transport infrastructure. The comparison with a traditional fluvial flooding approach, where a given discharge hydrograph is used as the only input to the hydrodynamic model, shows that the traditional approach fails to evaluate the activation of the minor tributary network, leading to an underestimation of potential infrastructure damages, and the inability to explain observed damages. These results suggest that hazard maps should explicitly model pluvial and compound pluvial-fluvial flooding when assessing risks to transportation networks. However, the findings also highlight certain limitations, including the need for more detailed and spatially distributed input data and increased computational time.