Land use/cover changes (LUCCs) in megacities can be rapid and extensive and lead to unintended consequences in sustainable watershed management. The aim of this study was to investigate effects of LUCC on hydrological components using Soil & Water Assessment Tool (SWAT) model in Terkos Basin, Turkey. Four LUCC scenarios (deforestation, urbanization, decrease in agricultural land and expansion in agricultural land) were set up regarding possible future land use changes in the watershed. Surface runoff was the main hydrological component that was impacted by LUCCs. Urbanization and conversion into agricultural lands scenarios resulted in considerable increases in surface runoff. Annual change of surface runoff for urbanization and conversion into agricultural lands scenarios was over 45% when compared to the baseline scenario. More remarkable changes were seen in dry months among the scenarios. Controlling the overall response of the hydrological systems to LUCC depends on better understanding of surface runoff processes. LUCC scenarios were also assessed based on freshwater availability components blue water and green water. The average annual total blue water potential, annual total green water flow and average green water storage of studied sub-basin were 537, 584 and 108 mm/year for the baseline scenario, respectively. The trends of the blue water flow and green water storage were similar for each scenario, in that they were closely related to precipitation. This study provides valuable insight into hydrological impacts of possible land use changes on forested watersheds.