Optimal sites for rainwater harvesting and proposed dams: A geospatial and analytic hierarchy process-based feasibility study in Western Saudi Arabia

This study focuses on an arid zone of Saudi Arabia that is experiencing rapid urban growth and escalating water scarcity. The region encompasses major cities such as Mecca, Jeddah, Khulays, and Rabigh, where the demand for sustainable water resource management is becoming increasingly urgent due to the limited availability of natural freshwater sources. The challenge is further intensified by ongoing urbanization and large-scale economic developments, particularly around Mecca, Jeddah, King Abdullah Economic City, and Yanbu Industrial City, which place additional pressure on the region’s fragile water systems. The objective of this research is to assess and map the suitability of rainwater harvesting (RWH) sites using an integrated approach that combines Geographic Information System (GIS), the Analytic Hierarchy Process (AHP), and Multi-Criteria Decision Analysis (MCDA). The analysis incorporates hydrological, geological, and infrastructural criteria, guided by Food and Agriculture Organization (FAO) guidelines. The study also evaluates the performance and contribution of existing RWH infrastructure and identifies optimal locations for future dam construction. The results indicate that approximately 6000 km² (∼26 % of the study area) is highly suitable for RWH, with an estimated surface runoff potential of about 730 million m³ . Existing dams—Khlays, Rabiigh, and Fatima—play a significant role in regional water supply. Four primary locations—Ghoran, Thule, Qahah, and Fatima—were identified as optimal for new dam sites, with estimated water storage capacities calculated. These findings demonstrate the potential of integrated RWH planning to enhance renewable water resources, support long-term water security, and inform policy and infrastructure development in arid regions like Western Saudi Arabia. • Existing RWH projects include Khlays, Rabiigh & Fatima dams. • GIS & AHP integration optimizes RWH site selection. • 26 % of the study area (∼6052 km²) is highly suitable for RWH. • Estimated surface runoff potential is about 730 million m³ . • Four optimal dam sites identified: Ghoran, Thule, Qahah, and Fatima.