Exploring the potential impact of rainfall extreme dynamics on river intersections

Railway systems represent critical transportation networks across Italy, ensuring socio-economic development. Due to their linear configuration and frequent intersections with watercourses, such infrastructures are particularly exposed to flood hazards. This analysis examines how evolving precipitation extremes interact with catchment response dynamics at railway–river intersections, with the goal of identifying critical spots (e.g., bridges, viaducts) that may face increased flood risk. Railway–river intersections are identified using OpenStreetMap and Copernicus EU-Hydro data, ensuring comprehensive coverage of the Italian railway network. For each intersection, upstream catchments are delineated from 25m EU-DEM data using D8 algorithm. These points serve as catchment outlets for a watershed-specific hydrological characterization, including area, channel length, slope, and time of concentration Giandotti (1934). A catchment analysis of approximately 9,400 railway-river intersections reveals significant spatial variability in time of concentration, which ranges from less than one hour in steep Alpine catchments in northern Italy to over 20 hours in the extensive plains of the Po Valley and southern regions (Figure 1-a). Time of concentration can define critical rainfall durations for each catchment, enabling identification of areas where this parameter corresponds to durations that may exhibit intensifying extreme events. This study aims to evaluate how these catchment characteristics interact with potential changing precipitation patterns. Long-term rainfall trends across Italy are obtained from the I²-RED dataset (1916–2022, covering 5,563 stations) that reveals significant temporal shifts in extreme rainfall behavior. Short-duration extremes (1-6 hours) are intensifying across the country, while longer-duration events show more complex, spatially variable trends (Mazzoglio et al., 2025). When examining precipitation trends specifically across railway catchment areas, a clear spatial variability emerges, with considerable changes for 24-hour extremes (0.95 quantile) reaching up to 1.5 mm/year increases in northwestern regions such as Liguria and southern Piedmont, while other areas show stable or declining patterns, as illustrated in Figure 1-b. Notably, around 29% of the examined railway-river intersections present a time of concentration between 2-7 hours, which overlaps with the duration range of precipitation extremes that are intensifying across Italy. Such conditions prove critical: catchments that respond faster to rainfall can overlap with the types of extreme events that are becoming more frequent and intense. Additional analyses examining the influence of catchment morphological characteristics (e.g., aspect and elevation) on precipitation trend patterns are being conducted to better understand orographic controls on extreme rainfall changes. The present study improves the characterization of flood risk at railway–river intersections, thereby supporting more informed infrastructure planning decisions and targeted flood mitigation measures to enhance railway network resilience in the context of ongoing climate change.