One of the climate change impacts is an increase in the severe drought frequencies. Recently, low flow frequency analysis has been considered in the study of hydrological drought. This study aims to forecast low flow by 2099 in the Kan River Basin in order to assess climate change impacts on low flow in this region. For this purpose, temperature and precipitation data were simulated by HadCM3 model using SDSM downscaling model under the scenarios A2 and B2 by 2099. Runoff simulation was estimated using SWAT while calibration and validation were implemented using the SWAT-CUP software and SUFI-2 algorithm. The optimal parameters obtained from monthly and daily calibration were projected via SUFI-2 algorithm. The results showed an increase in temperature but decrease in precipitation rate, which in the most pessimistic scenario, proves an increase in maximum temperature up to 4. 2 °C and for the precipitation, a decrease down to 10. 8% by 2099 is expected, as well. Furthermore, the accuracy analysis of the simulated runoff based on the monthly and daily calibration results showed a good fit between observed and simulated values. In fact, their correlation coefficient with the measured values differed less than 0. 03. Meanwhile for maximum flow values, daily calibration led to a more accuracy. The results of runoff forecasts showed a decrease in runoff, which is expected for spring and summer however an increase would be for autumn and winter. Overall, a 15 to 21 percent reduction in runoff was projected by 2099.