Expansion of unplanned agriculture and urbanization increases the danger of extreme flood and sedimentation. The Upper Awash basin has been under tremendous influence of human activities in the last five decades. The historical land use/land cover (LULC) change analysis was made by processing multi-temporal Landsat images and the future LULC was predicted using the Land Change Modeler. The LULC transition between a pair of classified LULC maps and driver variables were combined to predict the future LULC scenario. The five different LULC change and future land management scenarios are LULC 1974, LULC 2014, increase in the urban area, riparian and steep slope afforestation, and predicted future LULC 2045. The LULC change scenarios together with other spatial and climate data were used to simulate the hydrology, and sedimentation at four main subbasins using the calibrated soil and water assessment tool (SWAT) model. The mean monthly change in the water balance components and sedimentation have indicated higher rates of fluctuation due to LULC change. The riparian and steep slope reforestation scenario has reduced the mean annual surface runoff volume by 9.3% and sedimentation yield by 6.1% from the baseline LULC 2014. Moreover, the frequency of estimated 100-year annual extreme daily discharge reveals significant variation among the LULC scenarios. Notably, the future LULC 2045 has indicated a higher increase of extreme daily discharge by 23.5% at Homole subbasin. The study outlined the impact of land management on the flood events and sedimentation in the large basin, and spatial variation of LULC change impact has been presented. It suggests that the increase in deforestation due expansion of cropland and urbanization will intensify floods, whereas, riparian and steep slope reforestation has significantly reduced the peak discharge and sedimentation. Therefore, the future land management plans should consider appropriate vegetative conservation measures in the upland areas.