A THESIS SUBMITTED TO THE DEPARTMENT OF METEOROLOGY AND HYDROLOGY, SCHOOL OF GRADUATE STUDIES, ARBA MINCH UNIVERSITY FOR PARTIAL FULFILLMENT OF THE REQUERIMENTS FOR THE DEGREE OF MASTERS OF SCIENCE IN CLIMATE CHANGE AND DEVELOPMENT

Abstract

Climate change is a topic of discussion worldwide including Ethiopia. The present study assessed the possible impacts of climate change on runoff in the upper Birbir sub basin which is located in 8°48′17′′ and 9°22′19′′ N and 34°C49′39′′and 35°C37′27′′E; western Ethiopia. CORDEX-Africa data outputs of HadGEM2-ES for upper Birbir sub basin were selected under representative concentration pathways (RCP4.5& RCP8.5) scenario to make future projections in two time frames: mid-term (2041-2070) and long-term (2071-2100). After assessment of data quality; Bias, Coefficient of Variation and correlation were used to evaluate the systematic error of rainfall amount, degree of rainfall variability and the relationship of model outputs and observed datasets in addition to graphical plots. Trend detection was evaluated by Mann-Kendall trend test and sen’s estimators. Hargreaves method was used to estimate current and future evapotranspiration. HBV model was selected to simulate future stream flow for the projected climate variables . Coefficient of determination (R 2 ), Nash-Sutcliffe Efficiency (NSE), Relative Volume Error (RVE) and Root mean square error observation standard deviation ratio (RSR) were statistical tools used for performance evaluation of rainfall-runoff model (HBV) with a result of 0.82, 0.81, 5.70% and 0.11during calibration period. The observed annual rainfall shows upward trend except for Yubdo station, and temperature shows warming trend. Future projections of runoff will be expected to decrease in winter and spring while increase in summer and autumn, mainly followed the rainfall projected pattern. In mid-term, the annual average runoff projection will be expected to decrease by 2.05% and 1.35% under RCP4.5 and RCP8.5, respectively. In long-term, it will be expected to decrease by about 0.03% a nd 2.0% under RCP4.5 and RCP8.5 over upper Birbir sub basin. Keywords: Upper Birbir sub basin, Climate change, HBV, Trend detection, RCP and Runoff.