| Abstract: | The Awash River Basin is the most irrigated area in Ethiopia, which is facing critical
water resources problems. The main objective of this study was to assess the impacts of climate
change on river flows in the upper Awash Subbasin, Ethiopia, using the soil and water assessment
tool (SWAT) hydrological model. The ensemble of two global climate models (CSIRO-Mk3-6-0
and MIROC-ESM-CHEM with RCP4.5 and RCP8.5) for climate data projections (the 2020s, 2050s,
and 2080s) and historical climate data from 1981–2010 was considered. Bias-corrections were made for
both theGCMdata. SWAT model was calibrated and validated to simulate future hydrologic variables
in response to changes in rainfall and temperature. The results showed that the projected climate
change scenarios were an increase in rainfall for the period of the 2020s but reduced for the periods of
2050s and 2080s. The annual mean temperature increases, ranging from 0.5 to 0.9 C under RCP4.5
and 0.6 to 1.2 C under RCP8.5 for all time slices. In the 2020s, annual mean rainfall increases by 5.77%
under RCP4.5 and 7.80% under RCP8.5, while in 2050s and 2080s time slices, rainfall decrements
range from 3.31 to 9.87% under RCP4.5 and 6.80 to 16.22% under RCP8.5. The change in rainfall
and temperature probably leads to increases in the annual streamflow by 5.79% for RCP4.5 and
7.20% for RCP8.5 in the 2020s, whereas decreases by 10.39% and 11.45% under RCP4.5; and 10.79%
and 12.38% for RCP8.5 in 2050s and 2080s, respectively. Similarly, in the 2020s, an increment
of annual runoff was 10.73% for RCP4.5 and 12.08% for RCP8.5. Runoff reduces by 12.03% and
4.12% under RCP4.5; and 12.65% and 5.31% under RCP8.5 in the 2050s and the 2080s, respectively.
Overall, the results revealed that changes in rainfall and temperature would have significant impacts
on the streamflow and surface runoff, causing a possible reduction in the total water availability
in the subbasin. This study provides useful information for future water resource planning and
management in the face of climate change in the upper Awash River basin. |