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

The Gumara Watershed in Ethiopia’s Upper Blue Nile Basin is highly prone to flooding that damages crops, homes, and infrastructure. Steep slopes, intense seasonal, and land use changes increase flood risk. This study assessed flood susceptibility using the Analytical Hierarchy Process (AHP) and compared results with flood extent mapped from Sentinel-1 Synthetic Aperture Radar (SAR) imagery. Ten factors were used: Drainage Density (DD), Topographic Wetness Index (TWI), Distance to River (DR), Elevation, Slope, Hillshade, Aspect, Rainfall, Normalized Difference Vegetation Index (NDVI), and Land Use/Land Cover (LULC). Validation was performed using 74 ground truth flood points collected from field surveys and local records to evaluate the agreement between the AHP susceptibility map and the SAR-derived flood map. Results showed that 78 % of the watershed lies within Moderate to Very High susceptibility zones according to AHP, while SAR indicated that 73 % of the area was flooded. Rainfall, Elevation, and Slope were the most influential factors, followed by DD, LULC, and DR, while Aspect and Hillshade had minor effects. ROC analysis showed moderate accuracy for AHP (AUC = 0.79) and higher accuracy for SAR (AUC = 0.91). The comparison indicates that AHP identifies likely flood-prone areas, while SAR maps actual flood extent. These findings support flood risk management, early warning systems, and watershed planning in data-scarce regions. • Integrates AHP flood susceptibility with Sentinel-1 SAR flood mapping to assess flood risk in data-limited regions. • Rainfall, elevation, slope, drainage density, and land use/cover are key flooding drivers, improving watershed vulnerability insight. • Validation with 74 flood points and ROC analysis (AUC 0.79 AHP, 0.91 SAR) confirms reliable flood-prone mapping.