GIS-based identification of optimal rainwater harvesting sites to support irrigation in Egypt’s northwestern coastal region

Construction of dams in wadies for collecting rainwater, facilitating the creation of artificial farm ponds and percolation tanks are one of the potential strategies to overcome water shortages. within a Mediterranean watershed, focusing on Egypt's Northwestern coast region (NWCR). This study aimed to use a weighted overlay analysis tool for developing a methodology to identify appropriate rainwater harvesting (RWH) sites. To achieve this, the analytical hierarchy process (AHP) as an effective multi-criterion decision analysis tool (MCDA) was utilized in Al Raml watershed district on an area of 211.6 km2. This suitability analysis guides stakeholders to locate RWH structures that advance SDG 6 targets 6.4 (water-use efficiency) & 6.6 (aquifer recharge) and SDG 2 target 2.4 (resilient agriculture), while strengthening local climate-adaptation efforts under SDG 13. Various biophysical, hydrological, climate and socio-economic aspects were considered during criteria (such as rainfall, land use/land cover, soil type, slope, drainage density, stream order and distance to road and stream). It also utilizes SWAT model (Soil and Water Assessment Tool) to simulate runoff depth, infiltration, and sediment yield using remote sensing and GIS data then stored as GIS layers and integrated to develop a ranking system. Analysis indicates that 4.84 % of the study area is categorized as 'highly suitable'' for the construction of check dams, 34.84 % is '' moderately highly suitable,'' and 47.82 % is ''Low suitable.'' Only 12.5 % of the region was deemed ''unsuitable''. Whereas the suitability analysis for artificial farm ponds and percolation tank implementation revealed 36.3 %, 38.05 %, 24.91 % and 0.75 %, respectively. Finally, RWH techniques are recommended based on the weight and scale of the criteria and sub-criteria. Policy recommendations should focus on mandating RWHs, incentivizing retrofits, establishing clear guidelines, and embracing smart, and integrated systems with real-time monitoring to enhance efficiency and resilience against water scarcity and climate change.