Climate change is one of the most important challenges in front of mankind in the current century and especially future, which will intensify the hydrologic cycle and change the rivers flow regime. The Zayandeh-Rud River, as the most water filled river in the central plateau of Iran, has a strategic and important role in satisfying water resources for different consumption sectors in Zayandeh-Rud River Basin, and assessments of climate change impacts on the river flow is considered crucial. In this regard, this study will evaluate the climate change impact on the rate of Zayandeh-Rud Reservoir’s Inflow, as the most important structures in the basin, and also analyse different sources of uncertainty in the studies of hydro-climatic parameters. Hence, the monthly temperature and precipitation outputs of 22 GCM models in the Fifth Assessment Report (AR5) of Intergovernmental Panel on Climate Change (IPCC), were used in the baseline period of (1980-2005) and the period of near future (2020-2049) under emission senarios RCP2.6, RCP4.5 and RCP8.5. These ourputs were downscaled by the weather generator LARS-WG, for using in climatic studies at the case study. Consequently, the downscaled meteorological data were introduced to the calibrated AWBM, IHACRES and TANK hydrologic model and the procedure of simulating the reservoir’s inflow was performed under different climate change scenarios in the future period. As GCM models are one of the most important sources of uncertainty in climate change studies, by using Bayesian Model Averaging (BMA) the pattern of probabilistic weightening to their outputs was implemented in the period of (1980-2005). According to our findings, the BMA had acceptable performance in estimating hydro-climatic parameters of the baseline period and this approach was utilized for predicting hydro-climatic variables at the case study in the near future. Furthermore, the reduction of (5-10) % of the annual precipitation in the region’s meteorological stations would affect the rate of Zayandeh-Rud Reservoir Inflow. Besides, the rise of (0.85-1.07) ? C in annual temperature will intensify the climate change impacts of the basin’s water resources and cause the situation for decision makers and sector managers of Zayandeh-Rud River Basin become more complicated in the future period. All in all, the rate of reservoir’s inflow in months of winter will increase, however, the inflow of spring’s month will decrease by (10-40) %, which will intensify the water crisis for the following warm seasons. According to the results of this study, the reduction of (23-40) % for low flows in spring will cause some challenges related to meeting the needs of different consumtion sectors in the downstream regions of reservoir and shows the necessity of planning and changing the allocation of Zayandeh-Rud Reservoir in the near future. Key words: Climate change, Uncertainty analysis, Bayesian Model Averaging, Zayandeh-Rud Reservoir