Assessment of Land Use Impacts on Surface Runoff and Its Implication for Long-Term Planning, Using SWAT Model at Baro River Basin, Southwestern Ethiopia

Abstract

Assessing the effects of land use and land cover change on hydrology is important for long-term planning of water resource management strategies. This study aims to evaluate the impacts of land use and land cover change on surface runoff in upper Baro-river basin (Sore and Geba watershed) covering an area of about 6551 km2. Landsat images were used to analyze the land use and land cover change trends for the periods of three decades (1987-2015). The land use and land cover maps of 1987, 2001 and 2015 were generated from Landsat-5-TM, Landsat-7-ETM+ and Landsat 8 image, respectively. Maps were produced using the maximum likelihood algorithms supervised classification. The accuracy of the classified map was checked by confusion matrix. The accuracy measures index such as overall accuracy, user’s accuracy, producer’s accuracy and kappa statistics (?? ? ) were calculated and gives a satisfactory result. The trends of land use and land cover change showed that cultivated land is increased by 16.55% within the periods of between 1987 and 2015 with annual expansion by 36.15 km2 at the expense of other land use types such as open forest, dense forest and wood land. To evaluate the impacts of land use and land cover change on surface runoff three SWAT model setup were run using the produced land use maps. The sensitivity analysis, calibration, validation and uncertainty analysis of the SWAT model was assessed by SWAT-CUP computer program. Nine sensitive flow control parameters were identified and used for calibration of the model. The calibration of the model was carried out using the average monthly observed flow from Sore river gage from January 1996 to December 2000 and the validation of the model was carried out from January 2001 to December 2005. The performance of SWAT model was checked by using the values of coefficient of determination (R2), NashSutcliffe (NS), p-factor and r-factor. There was a good match between the simulated and observed flow during the calibration period with the values of R2 of 0.8, NS of 0.79, p-factor 0.78 and rfactor of 1.02 and for the validation period with the values of 0.75, 0.54, 0.78 and 1.26, respectively. During the periods between 1987 and 2015, a 16.55% cultivated land expansion was observed which may explain an increase of about 6.65 m3/s (32 mm) in annual surface runoff. In general, during the study period in Sore and Geba watershed the land use change influences the hydrology of the system (e.g., evapotranspiration, surface runoff and stream flow characteristics).