Flood susceptibility mapping in the Gumara watershed Upper Blue Nile Basin Ethiopia: AHP and Sentinel-1 SAR analysis

Study Region: The Gumara Watershed, located in Ethiopia’s Upper Blue Nile Basin, is highly vulnerable to seasonal flooding. This is driven by steep topography, intense rainfall during the rainy season, and ongoing land use changes that reduce infiltration and increase runoff.Study Focus: This study assesses flood susceptibility in the Gumara Watershed using the Analytical Hierarchy Process (AHP), integrating ten geospatial and hydrological factors. The resulting susceptibility map was classified into five risk zones and validated using ground truth data and Sentinel-1 Synthetic Aperture Radar (SAR) imagery. Model performance was evaluated through ROC curve analysis, with SAR used for comparative flood extent mapping.New Hydrological Insights for the Region: AHP identified 38.33% of the watershed as moderately susceptible and 8.08% as very highly susceptible. Sentinel-1 SAR detected 73.25% of the area as flooded, confirming broader inundation extents. Ground truth validation showed strong spatial agreement, with SAR achieving higher accuracy (AUC = 0.90) than AHP (AUC = 0.75). Sensitivity analysis revealed rainfall, elevation, slope, drainage density, land use, and river proximity as dominant flood drivers. These findings highlight the complementary value of predictive modeling and satellite-based observation for improving flood risk assessment and guiding watershed management in the Upper Blue Nile Basin.