IMPACT OF CLIMATE CHANGE ON HYDROLOGICAL PROCESS OF BILATE RIVER WATERSHED, RIFT VALLEY BASIN, ETHIOPIA

Abstract

The effects of climate change on hydrological regimes have become a priority area, both for process research, for water and catchment management strategies. Studying climate change on hydrological process is, therefore, a case for concern. Accordingly making impact assessment can provide information of the situation for which the corresponding solutions to be addressed. Therefore, this study presents impact of climate change on the hydrological process of Bilate River watershed, Rift Valley Basin, Ethiopia. CORDEX-Africa data output of Hadley Global Environment Model 2- Earth System (HadGEM2-ES) for Bilate catchment was selected under representative concentration pathways (RCP 4.5 and RCP 8.5) scenarios for making future climate projections. Initially, data quality and consistency for observed data was checked. In addition, the percent bias (PBIAS), coefficient of variation (CV), and absolute mean square error (AME) was used to evaluate the systematic error of rainfall and the relationship of observed and future model output. The assessment of trends in climate variables was carried out using Mann-Kendall’s tests and Sen’s slope estimators. The result of Mann-Kendall’s test indicated that, observed annual rainfall shows decreasing trend while the average temperature shows an increasing trend. The HEC-HMS model was successfully calibrated and validated and then forced with forecasted precipitation and temperature outputs from a suite of regional climate model (RCMs) corresponding to two different representative concentration pathways (RCP 4.5 and 8.5) for two time periods: 2017-2046 and 2047-2076 referred to as near-century and mid-century, respectively. Climate projections indicate that there will be modest increases in average annual precipitation and temperature in the future compared to the baseline (1987-2015) period. As, it resulted with R2=0.79, PBIAS=60% and NSE=0.89 for the calibration period while R2 =0.76, PBIAS=0.10%, and NSE=0.85 was obtained for the validation. Results of this study could be helpful for preparing any climate change variation plan to ensure sustainable water resources in the Bilate River watershed.