Application of Hydro-Economic Model in Optimal Distribution of Agricultural Water under Drought Conditions (Case Study: Irrigation Networks Downstream of Zayandehrud Dam)

Planning for optimal distribution of Zayandehrud Dam water to six Irrigation Networks (INs) located downstream of this dam was carried out based on a hydro-economic model under water scarcity conditions. The hydro-economic structure was developed through coupling the hydrologic simulation model (MODSIM) and economic optimization modelling approach (Positive Mathematical Programming, PMP). Water distribution priorities to the INs are based on the economic value of water used by crops in the current cropping pattern under different scenarios of normal (base year, 2014-2015) and drought conditions. Results showed that, in addition to the change in the priorities of water distribution throughout the six INs, the existing cropping patterns should also change. The order of water delivery to the six INs starts from Rudasht IN and ends with the Traditional IN. Also, the highest reduction in the area under cultivation in the base year, compared to the optimum cultivation, is related to alfalfa (in Nekoabad and Mahyar-Jarghouyeh INs), clover (in Rudasht and Abshar INs) and forage corn (Borkhar and Traditional INs). Beans cultivated area increases by 14 and 21% for Abshar and Rudasht INs, respectively. Based on the results, the economic value per m3 of water will rise on the average, if water is allocated on the basis of its shadow prices. Moreover, under drought conditions, the highest and the lowest increase in the economic value of water will take place in the Nekoabad IN (4,660 Rials m-3) and Rudasht IN (3,890 Rials m-3), respectively.