ASSESSING THE IMPACTS OF LAND USE/LAND COVER AND CLIMATE CHANGE ON UPSTREAM OF MELKA WAKANA RESERVOIR SEDIMENTATION, UPPER WABE SHEBELE BASINASSESSING THE IMPACTS OF LAND USE/LAND COVER AND CLIMATE CHANGE ON UPSTREAM OF MELKA WAKANA RESERVOIR SEDIMENTATION, UPPER WABE SHEBELE BASIETHIOPIAN

Abstract

Land use and climate changes are among the biggest issues facing the world today. The main purpose of this study was to assess the impact of land use and climate change on Melka Wakena reservoir sedimentation by using Geospatial tools and Hydrological models. Two time (1990 and 2016) land use land cover data and CORDEX-Africa data outputs of HadGEM2-ES regional climate model were used for this study along with other spatio-temporal data sets. T he data (1971-2000) was used for baseline scenario analysis. Future scenario analysis was performed in two-time frames: near-term (2020-2049) and mid-term (2050-2079) under selected representative concentration pathways (RCP4.5 and RCP8.5) scenarios. After assessment of missing, quality and consistency of data, bias, coefficient of variation and correlation were used to evaluate the systematic error of precipitation amount, the degree of precipitation variability and bias-corrected before serving as input to the impact analysis. Observed annual precipitation shows decreasing trend, whereas temperature shows an increasing trend. Impact assessment on sediment yield was done by Soil and Water Assessment Tool (SWAT) to simulate future sediment load for the predicted climate variables. Model performance was evaluated using coefficient of determination (R2), Nash-Sutcliffe Efficiency (NSE) and percent bias (PBIAS) during calibration and validation. The result of calibration and validation of sediment yield R2, NSE and PBIAS are 0.83, 0.79, 14.9 and 0.87, 0.82, 14.2 respectively. In this study the SWAT model yields average annual sediment load of 1430,and 1790.45 ton/ha/yr come into the Melka wakana Reservoir under LULC 1990, and 2016 respectively. The future precipitation predicted a decrease ,while temperature was increased in all RCP4.5 and RCP8.5 near and mid-term scenarios from the baseline period. These change in climate variables are result in an increase in mean annual sediment yield of 1.65% and decreaseby 23.09 % for RCP4.5 scenario and decrease by 19.88% and 18.84 % for the RCP8.5 scenario for the near and mid-term respectively. Finally,from this study we observed that the runoff and sediment yield of watershed show decreasing and increasing trends when we compare future scenario and land use of (1990_ 2016) respectively . Keywords: