The main objective of this study was to assess the impact of the environmental changes on thernhydrology and water quality of the Lege Dadi-Dire catchments. More specifically, the studyrnanalysed the land cover change scenarios that were assumed would have taken place in therncatchments, and the effect these changes have had on the hydrology and water quality of therncatchment. The Soil and Water Assessment Tool (SWAT) model was used to investigate thernimpact of land cover change on streamflow, sediment, nitrate, phosphorous, and otherrnconsidered water quality variables yield of the study area. The model was set up using readilyrnavailable spatial and temporal data, and calibrated against measured values.rnThere was good agreement between monthly estimated and simulated variables for therncalibration and validation periods. The simulation of sediment was slightly underestimatedrnbut overall, the agreement between the estimated and simulated variables was acceptable.rnTwo approaches have been taken to conduct the study. First, historical land use/cover data ofrn1960, 1980, and 2008 were taken and the impact of land use/cover change over the period wasrnanalysed.rnSecond, the 1990 land use/cover data was used as a base data and scenarios of the future landrnuse/cover were developed. Taking both cases, impacts of land use/cover and their scale werernidentified in this study.rnAccordingly, there has been close correlation between land use/cover, stream flow andrnturbidity. There has been a considerable increase in runoff of about 8.3% in Lege Dadirncatchment which is attributing to land use/cover effect.rnWithout climate change, land cover changes considered in the scenarios account for anrnincrease in runoff of about 3.4-49.9% and 14.9-15.3% for Lege Dadi and Dire catchmentsrnrespectively.rnSimilarly, the sediment yields have also increased more closely with agricultural land usernintensification.rnIn relation to the increase in agricultural land, nitrate, phosphorous and other consideredrnvariables have shown considerable increase through the application of agricultural inputs suchrnas fertilizers. This will further escalate the problem of water quality and treatment cost ofrnLege Dadi water treatment plant. Remedial measures have also been recommended