IMPACT OF CLIMATE CHANGE ON FLOOD FREQUENCY OF TEGONA RIVER, ETHIOPIA

Abstract

Climate change becomes main issue in the world. Our country Ethiopia is under its impact on many aspects. This study investigated the impact of climate change on flood frequency of Tegona watershed, Genale Dawa river basin, Ethiopia. For the future, CORDEX-Africa data output of HadGEM2-ES under RCP2.6, RCP 4.5 and RCP 8.5 for near-term (2021-2050) and mid-term (2051-2080) time horizons was selected. The biases of climate variables were removed by distribution based scaling (DBS) method and correlation coefficient(R2 ),

coefficient of variation (CV) and root mean square error (RMSE) were used to evaluate correction performance. Nonparametric Mann-Kendall test carried out to detect trends of observed and future projected climate variables. The result of MK test shows; the future precipitation will show decreasing trend except RCP4.5 in short-term period. Unlikely, average temperature and ET expected to show increasing in both time frames. Following this, MIKE 11 NAM-RR hydrological model was used to simulate future daily stream flow in both time horizons. Both determination coefficient (R2 ) and Nash Sutcliff values were 0.901 for calibration and 0.89 validation respectively. Annual maximum(AM) and peaks over threshold (POT) values were selected for flood frequency analysis. Based on selected model values, baseline period best fitted Log-Pearson-3 and General pareto distributions selected based on goodness of fit. For assessment, flood magnitude of future period was compared with baseline flood magnitude. As a result, the future flood in different time horizons under dominant RCP’s will expected to increase for both distributions for 2, 5, 10, 25, 50, 100, 200 and 1000yr return periods. In general, the increment of flood magnitude will have negative impact on the study area in the future and may cause damage or negative impact on agriculture practice, living standard, economic activity and downstream development water projects. So, management and adaptation measures with practices are recommended to rescue the area from flooding.