ASSESSING THE IMPACT OF LU/LC CHANGE ON HYDROLOGICAL RESPONSE BY USING SWAT MODEL: A CASE STUDY AT DEDABA WATERSHED, ETHIOPIA.

Abstract

Water is a precious and finite resource and must be managed in sustainable way to meet human as well as environmental needs. Land use/land cover change has an impact for alteration of watershed hydrology. The watershed is undergoing land use change due to intensive cultivation andurbanization as a result of population growth which has an impact on hydrologicresponse of the watershed. This study quantified watershed runoff volume using SWAT modeland assessed the effect of land use/land cover change on the stream flow. In this study, the impact of LU/LCchange was carried out by using the Soil Water Assessment Tool (SWAT2012) model, which was integrated with GIS10.3 software. GIS and ERDAS IMAGINE2014 were used to generate LU/LCmaps from Landsat TM, TM, and OLI acquired in the years 1990, 2001 and 2018 respectively. The land cover maps were generated using the maximum likelihood algorithm of supervised classification. The classified maps were assessed using confusion metrics. The results of the analysis showed that the Agricultural land has expanded during the study period of 1990-2018. During the study period, forest land, and shrub and grassland decreased by 19.5% and 15.61% respectively while Agricultural land and Built-up area increased by 33..63% and 1.48% respectively. Using three land cover maps, three SWAT model setup were run to evaluate the impacts of LU/LC changes on the streamflow of the study watershed. The performance of the SWAT model was evaluated through sensitivity analysis, calibrationand validation by using SWAT-CUP. The Coefficients of determination and Nash–Sutcliffe were used to evaluate the model and it resulted in 0.87 and 0.73 for calibration and 0.82 and 0.68 for validation respectively. During the study periods, the simulation result indicated that streamflow increased in the wet season and short rainy season streamflow by 9.64% and 3.05% respectively, while decreasing by 5.6% in the dry season. The Surface Flow (SURQ) increased by 12.58% while Groundwater Flow (GW_Q) decreased by 14.83% due to the increment of Agricultural land. The study resultsshowed change in flow with change in land use/landcover, so it needs landuse planning and sustainable water resource management