Simulation of the dynamics of water resources in the Hirmand watershed under economic and environmental scenarios

Water has been a hot topic in international disputes and negotiations in recent decades, and its management has been prioritized by governments. The system dynamics (SD) method is a management tool that allows users to interfere with model development in addition to explaining complicated systems of water resources by facts. The Sistan region is suffering from a water crisis due to its high dependence on the transboundary river of Hirmand, frequent droughts in recent two decades, and severe competition of different sectors for water consumption, so it needs modeling in which the present conditions of the region can be included and it can eventually help the management of the available water resources. This research aims to investigate the water resources in the Sistan region for their management and allocation under different managerial scenarios. The results show that scenarios like increasing irrigation efficiency, reducing evaporation loss, reducing cultivation area, adopting an optimal cropping pattern, and Afghanistan's adherence to Iran's water rights increase water resources and reduce water shortage. Among the 12 studied scenarios, the scenarios of adopting an optimal cropping pattern and Afghanistan's adherence to Iran's water rights are most effective in reducing water shortage so that they reduce water shortage by 440.61 and 643.94 million m(3) versus the base year, respectively, ultimately resulting in the alleviation of the agricultural water shortage. On the other hand, the scenarios of stabilizing dust and ensuring sustainable fauna and flora ecosystem can reduce water supply to the agricultural sector versus the base year. So, it is recommended to develop economic, social, and cultural ties with Afghanistan to ensure the release of water to Iran by this country. In addition, to cope with the issues and reduce water non-supply, it is recommended to adopt the scenarios of dust stabilization, sustainable fauna and flora ecosystem, and the development of cultivation area, as well as the scenarios of increasing irrigation efficiency, reducing evaporation, and adopting an optimal cropping pattern.