Geospatial Technique Integrated with MCDM Models for Selecting Potential Sites for Harvesting Rainwater in the Semi-arid Region

Severe droughts and mismanagement of water resources during the last decades have propelled authorities in the Kurdistan Region to be concerned about better management of precipitation which is considered the primary source of recharging surface and groundwater in the area of interest. The drought cycles in the last decades have stimulated water stakeholders to drill more wells and store uncontrolled runoff in suitable structures during rainy times to fulfill the increased water demands. The optimum sites for rainwater harvesting sites in the Qaradaqh basin, which is considered a water-scarce area, were determined using the analytical hierarchy process (AHP), sum average weighted method (SAWM), and fuzzy-based index (FBI) techniques. The essential thematic layers within the natural and artificial factors were rated, weighted, and integrated via GIS and multi-criteria decision-making (MCDM) approaches. As a consequence of the model results, three farm ponds and four small dams were proposed as future prospective sites for implementing rainwater harvesting structures. The current work shows that the unsuitable ratio over the study area in all methods AHP, SAWM, and FBI occupied 12.6%, 12.7%, and 14.2% respectively. The area under the curve (AUC) and receiver operating characteristics were used to validate the model outcomes. The AUC values range from 0.5 to 1, meaning that all MCDM results are good or are correctly selected. Based on the prediction rate curve for the suitability index map, the prediction accuracy was 72%, 57%, and 59% for AHP, SAWM, and fuzzy overlay, respectively. The final map shows that the potential sites for rainwater harvesting or suitable sites are clustered mainly in the northern and around the basin’s boundary, while unsuitable areas cover northeastern and some scatter zones in the middle due to restrictions of geology, distance to stream with the villages, and slope criteria. The total harvested runoff was 377,260 m3 from all the suggested structures. The proposed sites may provide a scientific and reasonable basis for utilizing this natural resource and minimize the impacts of future drought cycles.