Hydrogeophysical delineation of groundwater potential zones in the Al Uyaynah Area, Riyadh Region, Saudi Arabia, using vertical electrical sounding and HGPI-based analysis

Study Region The Al Uyaynah area in the Riyadh region of central Saudi Arabia lies within the hyper-arid Wadi Hanifa corridor. Groundwater is the sole reliable freshwater resource, hosted in a coupled Quaternary alluvial–Jurassic fractured carbonate aquifer system (Tuwaiq Mountain, Hanifa, Jubaila, and Arab formations). Rapid abstraction for agriculture and domestic supply has led to declining water levels and quality concerns, making local-scale aquifer characterization a priority for sustainable management. Study Focus We present a Hydrogeophysical Groundwater Potential Index (HGPI) based on 14 Schlumberger Vertical Electrical Soundings (VES) to map groundwater-prospective zones. One-dimensional inversion resolved a consistent three-layer system: a thin Quaternary surface cover, an unsaturated alluvial unit, and a thick fractured limestone aquifer. The revised HGPI integrates four non-redundant VES-derived parameters: depth to aquifer top (D), aquifer thickness (T), aquifer resistivity (), and surface-cover thickness (Q; Layer 1). Aquifer resistivity was scored using a trapezoidal membership function (optimal proxy interval: 25–45 Ohm.m) as an uncalibrated hydrogeophysical indicator of favorable saturation and water-quality conditions. The weighting scheme was tested by one-at-a-time sensitivity scenarios, top-threshold overlap metrics, Jaccard similarity, and Monte Carlo weight perturbation. New Hydrological Insights for the Region: The HGPI map delineates a coherent central-western-to-northwestern groundwater-priority belt associated with the most favorable combination of shallow-to-moderate aquifer access, high saturated thickness, and moderate aquifer resistivity within the coupled alluvial-carbonate system. The highest-confidence validation zone occurs along this continuous belt rather than as isolated point targets, while adjacent step-out areas should be treated as secondary targets because their ranking is more sensitive to weighting choices and resistivity interpretation. Low-resistivity sectors remain lower-confidence targets because the response may reflect saline water, clay/marl intervals, enhanced saturation, or changes in fracture density. Sensitivity analysis shows that the core priority belt is robust, whereas the marginal zones can reorganize when resistivity and surface-cover weights change. Therefore, the HGPI product is presented as a reconnaissance-scale screening map to guide 2D ERT, pilot drilling, pumping tests, and EC/TDS calibration before final production-well siting.