Estimating Surface Runoff Potential in the Abyan Delta, Yemen Using GIS-Based SCS-Curve Number Method

Abstract

A GIS-based Soil Conservation Service Curve Number (SCS-CN) approach was used to estimate surface-runoff potential in Yemen’s arid Abyan Delta (∼1,237 km²). Sentinel-2 (10 m) imagery was classified into major land-cover types and combined with hydrologic soil groups (HYSOGs) to assign CN values under Antecedent Moisture Condition II. The composite CN map (67–100; mean = 91.8) indicates limited infiltration across large areas of bare or impervious surfaces on clayey soils. Using the standard SCS-CN equations, event runoff was simulated for representative storm depths of 74, 124, and 174 mm. The model produced direct-runoff depths of ∼52, 100, and 150 mm, corresponding to runoff coefficients of ∼71%, 81%, and 86%, and basin-wide volumes of 0.65, 1.24, and 1.85 × 10⁸ m³, respectively. Spatial attribution shows that high-CN zones (notably barren HSG-C/D units and built-up/roads) generate most of the runoff despite covering a smaller fraction of the delta. The results identify priority areas for spate-irrigation, retention, and recharge interventions, and provide a reproducible baseline for flood-risk reduction and water-harvesting planning in data-scarce drylands. The workflow can be readily updated with improved soils, land-use, or climate inputs to support adaptive management.