Surface runoff is considered one of the most significant water resources in arid and semi-arid environments. Estimating the volume of surface runoff through the application of Geographic Information Systems (GIS), along with maps detailing the geomorphological and geological characteristics of the Wadi Haran basin, is an essential process. This estimation is supported by mathematical equations based on the Soil Conservation Service Curve Number method (SCS-CN), which is among the most widely used approaches for calculating runoff volume. The study area, Wadi Haran basin, covers approximately 1,895 km². The Curve Number (CN) was found to be 92, with runoff volume (QV) values ranging between 582.71 m³ and 12.85 m³. The total surface runoff was calculated to be 198.2 m³. These results confirm the presence of significant surface runoff in the northern and northeastern parts of the basin. This is primarily attributed to the wide basin area and the presence of hard, low-permeability geomorphological soil characteristics that contribute to water accumulation and surface flow, rather than infiltration into the soil. Conversely, the southwestern part of the basin, characterised by higher-permeability geomorphological features, exhibits lower surface runoff. Overall, the basin is characterised by increased surface runoff rates, particularly in the northern and northeastern sections, due to the broader basin area and low soil permeability compared to the southern and southwestern areas.
