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Scientific findings indicated there is climate change that affects given hydrology and, hence, water availability worldwide. To quantify its impact on a specific catchment scale, since spatial and temporal variability of climate change impact, this study was carried out at Ribb catchment, Lake Tana basin, Ethiopia. The catchment hydrology was represented by the Soil and Water Analysis Tool (SWAT) through using historical observed data. Regional Climate Model (RCM) projection data set for Nile Basin studies at Representative Concentration Pathway (RCPs) (RCP4.5 and RCP8.5) were used for future streamflow generation on three-time horizons; 2020s (2011–2040), 2050s (2041–2070), and 2080s (2071–2098). A baseline period (1976–2005) was used as a reference. SWAT was calibrated (R2 = 0.83 and NSE = 0.74) and validated (R2 = 0.72 and NSE = 0.71). The analysis was done based on the changes from the baseline period to the 2080s. Temperature showed an increasing trend but rainfall is decreasing. The mean annual streamflow could potentially reduce from 42.78 m3/s to 40.24 m3/s and from 42.78 m3/s to 37.58 m3/s based on RCP4.5 and RCP8.5 scenarios, respectively. On a monthly time scale, decreases in streamflow were found from March to August whereas there was a slight increase from September to February. Concerning individual months, June flows were found to have maximum impact in both scenarios (63.3% at RCP8.5 and 55.45% at RCP4.5 scenarios). The least impacted month was August based on the RCP8.5 scenario which is decreased by 6.64% and April based on the RCP4.5 scenario which is reduced by 1.21%. Looking at total volume, July showed a maximum decrease in both scenarios which is reduced by 21.08 m3/s at the RCP4.5 scenario and 51.22 m3/s at the RCP8.5 scenario. The maximum increase was found in October with 10.31 m3/s and 11.26 m3/s at RCP4.5 and RCP8.5 scenarios respectively. The future streamflow of Ribb River has decreased annually and monthly due to increasing temperature and reduction of rainfall. HIGHLIGHTS The research was done using the current RCP scenarios.; The research work focuses on future climate change impacts of the streamflow.; It is done on the different time horizons are predicted the climate change impact on the hydrology of a given catchment for a long period (up to 2100).; It used direct observed data to the stations to calibrate the model.