The Impacts of Climate Change on Rainfall and Flood Frequency: The Case of Hare Watershed, Southern Rift Valley of Ethiopia

Abstract

Hare River watershed is located in the Abaya-Chamo sub-basin of the southern Ethiopian Rift Valley and drains to Lake Abaya. The study aims to determine the impacts of climate change on rainfall and flood frequency of Hare watershed. In the study the daily data values of rainfall and discharge from 1980-2006 was used based on stream flow measurements carried out by MWIE. The downscaled climate data such as, RCP4.5 and RCP8.5 was used for the future period assessment. Both rainfall and flood frequency analysis was performed using Log-Pearson type III methods for return periods (T) of T = 2 yrs, 5 yrs, 10 yrs, 25 yrs, 50 yrs and 100 yrs. The annual peak flow frequency analysis has been carried out for the future (2020s, 2050s and 2080s) periods using the U.S. Army Corps of Engineers Statistical Software Package (HEC-SSP). RCP8.5 scenario for all return period by 2050s and 2080s predicted an increasing the change in rainfall magnitude. RCP4.5 scenario for all return period by 2020s and 2050s predicted decreasing rainfall magnitude. RCPs scenario predicted the 100-years flood of the current climate seems to increase to a flood return period of (2 yrs, 5 yrs, 10 yrs, 25 yrs and 50 yrs). The rainfall frequency analysis shows climate change will have impact on the frequency and magnitude of rainfall intensity. The future change in rainfall magnitude clearly governs in peak flow magnitude and frequency. Uncertainty analysis is recommended to assess the uncertainty associated with the bias correction method.