EVALUATION OF THE IMPACTS OF CLIMATE CHANGE ON THE STREAM FLOW IN MELKA WEKENA CATCHMENT UPPER WABE SHEBELLE WATERSHED SOUTH EASTERN, ETHIOPIA

Abstract

Water resources in the Melka Wakena Catchment Upper Wabe-Shebelle Watershed have been less explored concerning the impact on hydrology that the future climate will have. This aimed to analyses impacts future climate change scenarios on streamflow in the Melka Wakena Catchment Upper Wabe-Shebelle Watershed in South Eastern Ethiopia are evaluated by using the outputs of four climate models for two representative concentration pathway (RCP) climate scenarios, which are RCP 4.5 and RCP 8.5. Streamflow simulation was done using the HEC HMS rainfall-runoff model. The model was calibrated and validated at an outlet of the catchment station using observed streamflow data. The model's performance was measured as an NSE of 0.64 during calibration (1995–2008) and 0.71 during validation (2009–2015). The model was calibrated and validated to simulate future hydrologic variables in response to changes in rainfall and PET. The estimated average annual PET in the catchment in the near term (2021–2050) of both emission scenarios is projected to increase from 5.15% to 6.04%, and in the mid-term (2051–2080) the average annual PET is projected to increase from 10.28% to 13.17% under both scenarios. In the near term, the average annual rainfall change is projected to be between -11.36% to +10.38%) under RCP4.5 and (-12.91% to +53.28%) under RCP8.5. On the other hand, mid-term climate models projected emissions ranging between -16. from+6.18%) under RCP4.5 and (-12.3% to 85.14%) under RCP8.5. Baseline (1971–2000), near-term (2021–2050), and mid-term (2051–2080) projections. Almost all of the models' projections in the study area indicate that streamflow will likely decrease from October to November under both emission scenarios, and from April to October in the mid term under both emission scenarios. These decrements are dominantly from October to November within -6.21 from22% in the near-term period and -7.4 to -0.76% in the mid-term period. The result obtained showed that the precipitation was predicted to be mildly decreasing, whereas overall annual flow was projected to be insignificantly decreasing under RCP4.5 and RCP8.5 scenarios. This study provides helpful information for future water resource planning, water Storage, and management in the Melka Wekena Catchment Upper Wabe-Shebelle Watershed in the context of climate change on streamflow.