Abstract:
The study investigated the climate change impact on the frequency of flood flows for the
Abelti-catchment in the Upper Omo-Gibe river basin in the southwestern Ethiopia by using
the HadGEM2-ES climate model outputs of RCP 2.6 and RCP 4.5 under CMIP5 for the
future two horizons 2020`s (2021-2050) and 2050`s (2051-2080). Areal annual mean and
seasonal rainfall, minimum and maximum temperature and evapotranspiration are
projected and Nonparametric Mann-Kendall statistical test was used to detect trends in case
of the annual mean. Then a continuous daily hydrologic model (HEC-HMS) was used to
generate daily flow series for the baseline and for the future time horizons. Lastly, flood
frequency was analyzed considering peak over-threshold and annual maximum data series
by using General Pareto distribution and Generalized Extreme Value Distribution,
respectively for the current, baseline and future. The results showed increment in trend and
in percentage of all selected climate variables in both periods except rainfall, which showed
variability over the catchment. The value respectively of calibration and validation R
2
; 0.82
and 0.78 and NSE; 0.74 and 0.75 that shows satisfactory performance of the model. The
streamflow is expected to increase and decrease annually in the future projection (-2.70%
and 0.065%) in 2020`s and (+3.48% and +9.72%) in 2050’s under RCP 2.6 and RCP 4.5
respectively. Recurrent flood frequency increased in both directions in the future under
both scenarios projection. The increase in flood magnitude in the area may have a
significant negative effect on the sustainability of existed agriculture, life of the community
and hydropower development projects at downstream. Moreover, it may lead to unexpected
flood and flood hazards. Therefore, adaptation measures are recommended to be sought for
possible flooding in the flood plain areas of the River basin at downstream.
