Aassessing the Future Climatic Effects on the Hydrology of Qarahsu Watershed

Attention to the phenomenon of climate change and its impact on water resources is of great importance. The aim of this study is to evaluate the effect of different methods of weighting the output of AOGCM models and its effect on runoff in Qarahsu Basin during the period 2041-2021. The best climatic models (HADGEM2-ES, MICRO IPSL-CM5A-LR, NOERESM1-M, ESM2M-GFDEL) were selected from 14 general circulation models and weighed with three weighting methods including the same method, Bayesian averaging method and REA method. The results showed that the highest increase of maximum temperature in summer was 1.58 ° C by the same weighting method and the lowest increase of minimum temperature in winter with REA method was 0.96 ° C. The highest percentage of precipitation changes was in August with the same method and the lowest percentage of precipitation changes was in February with REA method. Evaluation of SWAT model simulation results for calibration period using R2 and NS statistical indices in calibration stage is equal to 0.74 and 0.79 and in validation stage is 0.68 and 0.72, respectively, which indicates the accuracy of the model in a runoff simulation. Prediction of runoff changes with the approach of ensemble the output of climate models, shows reduction in runoff in the future period. The lowest and highest percentages of runoff changes will be corresponded to Bayesian method which is -13 and -34.4%, respectively. Overall, the results indicate a change in the temporal distribution of flow in the Qarahsu Basin in the coming period, which will cause significant changes in the quality and quantity of water resources.