In recent decades, water scarcity has become a global problem due to global population growth and increasing per capita water consumption. Increasing greenhouse gases in recent decades and rising temperatures have caused widespread climate change in most parts of the globe. Therefore, awareness of the climate and water resources in each region is an important step in planning and managing water resources and preventing potential hazards such as future floods and droughts. From this perspective, hydrological modeling in watersheds is important. This study aimed to investigate and evaluate the flow of the Plasjan River, using the WetSpa hydrological model in future periods, affected by climate change in the Eskandari Watershed, which is one of the sub-basins of the Zayandehrood River. In this study, the synoptic Daran and Fereydoon Shahr stations were used to collect meteorological data in the Eskandari basin and daily data of the Eskandari hydrometric station located at the outlet of the basin were used to study the flow of the Plasjan River.In order to conduct the present study, the ability of WetSpa model to simulate river flow was firstly evaluated and the watershed maps were extracted using WetSpa model. Then, the ability of the LARS-WG model to evaluate the exponential scaling of GCM general circulation model’s data was evaluated.Then, using the LARS-WG model, climatic data were generated in the near future (2021-2040) and the distant future (2041-2060) under different scenarios RCP 2.6, RCP4.5, RCP 8.5.The WetSpa model calibration and validation process was then performed. Future climatic data generated in the previous step, along with digital elevation maps, soil texture and land use, were input to the WetSpa model. And river runoff was calculated in the near future. The results of the calibration and validation of the WetSpa model showed that the model has an acceptable ability to simulate river flow. According to the studies, if the Nash Sutcliffe coefficient is obtained between 0.50 and 0.65, it indicates good and acceptable model capability in simulating basin hydrological processes. In this study, the Nash Sutcliffe coefficient was 0.55 in the calibration stage and 0.54 in the validation stage. Which showed that the model has a relatively good ability to simulate flow in the basin. To evaluate the LARS-WG model, maximum and minimum precipitation and temperature statistics during the baseline period 1992 to 2005 were used. The results of the study of the effect of climate change on the temperature component of the region showed that the temperature of the study area is about 1.5 to 3 ° C by 2040 (near future) and 2.5 to 4.3 ° C by 2060 (far future). will increase. The results show that temperatures will rise throughout the year except January, with the highest increase in July. Also, the effects of climate change on precipitation component showed that precipitation increased in March, October and November and decreased in other months. The percentage of increase in precipitation will be between 7 and 37 percent. The highest drop in precipitation will be in May and around 27% under the RCP8.5 scenario in the near future. The results also show that basin surface runoff will decrease in all months to 2060, compared to baseline, under all climate change patterns. The largest reduction in runoff over the base period will occur in April. Runoff will also decrease by 2060 at the basin outlet, in the most optimistic state, by 15% and in the most optimistic state, by about 65% over the baseline period. Keywords: Climate Change, Surface Runoff, Plasjan River, RCP Scenarios, WetSpa Hydrological Model