EVALUATION OF THE IMPACT OF LAND USE LAND COVER CHANGE ON STREAM FLOW: A CASE STUDY OF HOLETA SUB WATERSHED, AWASH SUB BASIN, ETHIOPIA

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ABSTRACT Understanding the land use cover change (LULCC) and its implication on surface hydrology of the Holeta sub-watershed is vital for the management and utilization of water resources in the catchment. The impact of LULC changes on streamflow was not understood in this study area. The objective of the study was to evaluate the impact of LULC change on streamflow of the catchment using satellite data and hydrological modeling. The LULC change detection was done using remote sensing techniques (Landsat images) and the images were processed, classified and analyzed using Earth Resources Data Analysis System (ERDAS) imagine 2015 software. The land cover maps were done using supervised type of image classification. The accuracy of classified maps was assessed using an error matrix/confusion matrix and the assessment showed that the classification was acceptable. SWAT model was used to investigate the impact of land cover change on streamflow of the study area. Calibration and validation of streamflow were carried out using the SUFI-2 algorithm in SWAT_CUP2012 for the years 1985-2000 and 2001- 2009 respectively. Land cover analysis has shown that agricultural land and settlement area increased from 30.19% to 57.10% and 15.40% to 26.03% respectively between 1984 and 2018, while forest land has decreased from 5.54% to 4.33%, shrubland from 14.46% to 3.93%, and pasture land from 24.75% to 4.92%.The modeling result showed that there was an agreement between observed and simulated streamflow with coefficient of determination (R2) and Nash Sutcliffe efficiency values of 0.76 and 0.85 for calibration, 0.68 and 0.80 for validation respectively. The evaluation of SWAT hydrologic response unit (HRU) due to LULC change showed that monthly streamflow was increased by 28.15% in wet months and decreased by 51.42% in dry months between the years 1984 and 2000 while between 2000 and 2018, it was increased by 44.8% and decreased by 11.76% for wet and dry months respectively. Similarly, surface runoff was found to increase and groundwater decreased during the study period. This change in the hydrological component is the direct result of the LULC change of the area. This suggests an urgent need to regulate the LULC in order to maintain sustainable water resources management planning in the catchment. Key words: Holeta Sub-Watershed, LULC, Remote Sensing, SWAT, Hydrologic modeling, Stream flow