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.
