Assessing the Spatial Supply-Demand Balance of Hydrological Ecosystem Services in Iran's Semi-Arid Watersheds (Case Study: Karkheh Watershed)

The research aimed at the water yield supply-demand mapping and its spatial matching in the Karkheh watershed in Lorestan province. At first, the water supply was estimated using InVEST 3.9. To this end, evapotranspiration, annual precipitation, land use/land cover, plant available water content, and the root depth restricting layer were entered into the model. The periods of 2003-2012 and 2013-2017 were chosen respectively for calibration and validation. Then, the water demand was calculated based on the agriculture water demands and urban and industrial consumptions. Water efficiency was determined from the difference between water supply and demand. Finally, the spatial balance of water supply-demand was evaluated with the RWBI index in each sub-basin. According to the results, for the annual water consumption of 746 Mm3, 1655.7 Mm3 of water was produced. Sub-basins S2, S19, S5, and S23 had the highest water yield and efficiency respectively with 220.2, 155.4, 149.2, and 136.2 Mm3. Water yield in pixel scale was calculated from 0 to 526 mm and S9, S2, and S1 sub-basins had the highest per-pixel water yield. Based on the results, water supply-demand imbalance was observed in S14, S15, and S4 (RWBI < 0) while S19, S23, S2, and S5 sub-basins had the highest spatial balance of supply-demand (RWBI > 0). According to the results, the spatial differences in water supply-demand are influenced by parameters such as land use, precipitation, and evapotranspiration and reflect the management decisions taken in the study area.