HYDROLOGIC RESPONSE TO LAND USE/LAND COVER CHANGE IN THE GENALE DAWA RIVER BASIN, ETHIOPIA

Abstract

Land use land cover change has been one of factors responsible for altering the streamflow of the watershed on the Genale Dawa river basin leading to impacting river flows. The study mainly focused on estimating land use land cover change on streamflow. Land use land cover maps of 1986 and 2013 were obtained from Ethiopian Mapping Agency. The maximum likelihood algorithm of supervised classification was used in ERDAS Imagine 2014 software tool. A physical based, semi-distributed hydrological model, SWAT was used to investigate the impact of land cover change on streamflow of Genale Dawa River Basin gauged at Halwen. Land cover change analysis has shown an increment of cultivated land from 9.5% to 17.6%, agriculture land 9.1% to 19%, and built up areas 5.2% to 14.4%, while a decrement in the forest area from 31.15% to 19%, and water body from 7.2% to 7%, shrub land from 15.9% to 8.2%, Wet land from 8.8% to 4.9% and Grass land from 13.2% to 9.6% between 1986 and 2013. The performance of the SWAT model was evaluated through sensitivity analysis, calibration and validation. The model was calibrated using flow data from 1990 to 2001 including 2 year warm-up period and validated using data 2002 to 2007. Both the calibration and validation result show good agreement between observed and simulated stream flow with NSE and R 2 values of 0.86 and 0.88 for calibration and NSE are 0.84 and 0.85 for validation. Sensitivity analysis has shown that the curve number is the most sensitive parameter that affects stream flow of the watershed. The result of this study indicated that the mean monthly stream flow were increased by 8.5% for wet season and decreased by 3% in the dry season over 30 year’s period. As a result it might be possible to conclude that for the catchments the impacts were significant. Therefore, it can be deduced that LULC impact for the study area might be the most sensitive than the propagated uncertainty on catchment flow.