Post-Fire Urban Runoff Assessment in a Mediterranean Basin Using Integrated UAV–SWMM–HEC-RAS Modelling

Abstract. Understanding urban hydrological systems in the Mediterranean environment is a crucial scientific and practical issue, particularly the disturbances caused by heavy rainfall and forest fires, which affect seepage dynamics, surface roughness, and drainage efficiency. This study presents an integrated hydrological spatial scenario combining high-resolution UAV-photogrammetry, GIS-based analysis, and SWMM-HEC-RAS-2D modelling to simulate the post-fire runoff response in a Mediterranean urban basin. A digital surface model derived from drones (0.2 m resolution) and an orthomossayic model (5 cm GSD) were used to extract topographic gradients, land cover classifications, and surface roughness parameters to generate hydrological inputs. The SWMM-HEC-RAS composite product was calibrated and validated using field rainfall and runoff measurements collected throughout hydrological seasons.

The model was largely successful in characterizing the variability of runoff generation based on observed rainfall intensities, demonstrating strong predictive ability during moderate storm conditions while exhibiting increased uncertainty during rare high intensity events. The spatial analysis showed that post-fire landscape changes and loss of vegetation cover affected soil hydrophobicity significantly exacerbated runoff and flow, and increased peak discharge volumes. This framework, combined with high quality geospatial data was able to effectively describe flood prone areas and quantify the influence of key urban parameters including surface infiltration, topographic slope and engineered drainage networks on flood dynamics. This research underscores the value of UAV data for improving hydrodynamic modelling and creating practical flood-risk and stormwater-management tools in fire-affected areas, while also supporting the broader ISPRS goal of using geospatial technologies to plan sustainable and climate-resilient water infrastructure.