ABSTRACT Changes in land use land cover results major change in all scale basin condition and hydrological response. The human impact of watershed land use land cover change and climate change on hydrological characteristics of watershed processes of stream fl.ow have been widely studied. Geographic Information System (GIS)-bilsed spatial modeling has play a crucial tool in land use land cover and climate change impact on runoff and sedimentation studies . The Soil and Water Assessment Tool (SWAT) model is one of many hydrologic tools that is effective tool for assessing water resource with the help of GIS and it is also important for studying nonpoint-source pollution problems for a wide range of basin scales and watershed degradation over a long time series. The major objective of this study was to evaluate the impact of historic land use land cover change on hydrological dynamics of Koga watershed by using SWAT model. The SWAT model used various inputs; DEM, Land Use Land Cover, Soil, Climate and Meteorological data. Four (1973, 1986, 2001 and 2013) land use land cover classifications for the watershed were developed from Landsat MSS, TM, ETM+ using supervised classification system. Six land use land cover classes were identified for 197 3, 1986 and 2001 but 2013 la,.d use land cover found one additional land use system, because of artificial dam. Land use land cover results have shown that forests land had declined between 1973 and 2001by 63.6% while agricultural land and built-up area expanded by 27. 7% and JO. 7% respectively. Instead a Forest area has shown increment between 2001 and 2013 from 3.6 percent to 8.4 percent in cost of other land use land cover classes. To evaluate the impact of land use land cover change on Koga watershed hydrology the SWAT model was calibrated, validated and twelve stream flow parameters were selected to be sensitive for the stream fl.ow of the watershed and used for automatic and manual model calibration. The model efficiency is f6aluated in terms of R2 and NS objective function and result for calibration 0. 76 and 0. 7 5 respectively al'llfor validation it result 0. 70 and 0.66 respectively. Evaluation of the impact of land use land cover changes revealed that there was an increase of stream flow from 3.88 to 4.49 m3/s in 1973 to 1986 and 2001 stream flow increase 20.48% whereas 2013 stream fl.ow decreased by 28. 84 percent because of high forest coverage than 2001 l and use land cover. Three scenarios developed and impact on stream fl.ow evaluated. If Koga watershed covers only by Forest, Built Ups, Wet land and Cultivation land the stream fl.ow will decrease by 30.4 percent from 2013 stream fl.ow record. Second scenario consider if Koga watershed covered by only Cultivation land because of this change the stream fl.ow will increase by 56.89 percent from 2013 stream fl.ow record, but if the watershed only cover by forest land the stream flow will decreased by 51.43 percent. The study recorded a change in stream flow when the land use land cover of the watershed changes. Based on this result changes in land use land cover have impact on hydrology of Koga watershed. The results will further help in making decisions related to watershed management options that will promote sustainable utilization and management of Koga land and water resources. Keywords; - SWAT, Koga, Land use Land cover, Calibration, Validation, Sensitivity Analysis