Economic, social, and demographic development has globally led to an increased demand for water, consequently forcing some countries to face the shortage of water resources. In Iran, the problem of water scarcity is such a serious challenge that the sustainable allocation of water resources is sought after so as to help deal with this crisis. To this aim, the present paper proposes a new Robust Fuzzy Stochastic Programming model for the allocation of water resources. For the first time in the literature of stochastic water allocation problem, we applied the sustainability index to the optimization model and considered different levels of groundwater in an allocation system. Another feature of this model is its capability in considering a hybrid uncertainty in the parameters of the model, i.e. fuzzy stochastic scenarios, in a robust fuzzy stochastic programming model. Our proposed model considers three objective functions, namely maximizing the profits of different consumption sectors, minimizing the loss of different sectors caused by water shortage in different scenarios, and minimizing the allocation of salt water from ground water. The model has been applied in Mashhad city, northeastern Iran, which has long had water scarcity as an issue. We studied the allocation of water from surface, ground, and recycled wastewater resources to the three sectors of agricultural, municipal, and industrial; the results indicated that water allocation patterns and water shortages were affected by different scenarios. In fact, the municipal and agricultural sectors did not face water shortage in all scenarios, whereas the industrial sector encountered water scarcity in a drought year. Moreover, the assessment of optimality and feasibility robustness of the model indicated that the proposed model is robust.

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