Due to population growth and increasing demand for water in agriculture, industry and urban along with environmental demands, the issue of supplying and distributing the good quality water became a serious challenge for water resources managers and policy makers. One of the approaches discussed in recent decades is conjunctive use optimization of surface water and groundwater. The aim of this study is to derive the operation policies for surface and groundwater resources using conjunctive hedging rules and the experience and knowledge of water experts. Besides the assessment of climate change impacts on water resources of Zayandehrud River Basin considering uncertainty, another goal is to optimize conjunctive use of basin water resources. Studies show increase in temperature, decrease in precipitation and successive droughts as the effects of future climate change. Also the results of some studies about future climate change of our country indicate increase in temperature, heavy rainfall events and flooding and decrease in snowfall. In addition climate change will have a significant impact on increment of domestic and agriculture water demands. Also changes in rainfall amount along with temperature rise and decrease in snow cover, will affect both quantity and quality of water resources. Changes in temperature and precipitation patterns lead to changes in runoff from rainfall and this issue can affect the water supply of dam reservoirs, discharge of the rivers and groundwater recharge rate, especially during dry seasons. Being located in two different provinces, inter-basin water transfer, different hydrological and climatic conditions, interaction of surface water and groundwater and several kinds of water demands are complexities which Zayandehrud River Basin is faced with. Deriving an optimized conjunctive operation policy is one of the most important goals of this study and all of the mentioned issues should be considered for obtaining such policy. In this dissertation WEAP model is used for simulation and Gravitational Search Algorithm is applied as optimizer. Since the optimization process needs multiple simulations to be done, GSA and WEAP were linked within the Matlab environment. Initial answers are produced in optimization algorithm and each one is assessed in simulation model. In the next step the results return to the Matlab environment for evaluating the objective function and this procedure continues to obtain the optimum policies. To evaluate the performance, resulted policies were applied for a period in the future and under climate change impacts. In this regard, 15 General Circulation Models were used, also to evaluate the uncertainty, bounded range with known probability distribution and weighting methods were applied. The results show unsustainable condition of aquifers located in Zayandehrud Basin and if the current management system continues, Zayandehrud River Basin will face significant problems. Of course operation management of water resources with optimum policies will help to improve the mentioned condition. Utilizing optimized conjunctive operation policy caused an increase in demand sector group sustainability index of 11% and 3% compared with trend policy and dam reservoir hedging policy respectively. According to water resources group sustainability index, using conjunctive hedging policy caused an increase in sustainability of 2% and 6% compared with dam reservoir hedging policy and trend scenario respectively. Mentioned consequences indicate appropriate performance of conjunctive hedging policy in comparison with other studied operation policies. As a result, conjunctive hedging policy can be considered as an efficient solution to overcome the water crisis in Zayandehrud River Basin. Keywords: Water Resources Management, Climate Change, Uncertainty, Conjunctive Use, Hedging Policy, Gravitational Search Algorithm, Zayandehrud River Basin.