Abstract:
The main purpose of this study was conducted to understand the climate change
impacts on surface water availability of Robigumer and Beressa River catchments in Jemma
sub basin in Abbay Basin. The Soil and Water Assessment Tool (SWAT) model was
applied to study the current (1984-2008) and future scenarios (2026-2100) runoff magnitude
in the catchments and associated uncertainty with the simulated outputs. The model was
calibrated for the period of 1984 to 2000 and validated for the period of 2001-2008. The
flow parameters that significantly limit the runoff in the catchment and the model
uncertainty were assessed using SUFI2 in SWAT–CUP. Cn2, Esco, Canmx and Cn2, Esco
and Blai, were the most significant parameter in Beressa and Robigumer catchment
respectively. The future climate change impact studies on water availability of the
catchments were done based on the outputs of the RCM Model, A1B emission scenarios. In
terms of hydrological model performance the model efficiency magnitude for Beressa and
Robigumer catchment is ENS (0.69, 0.75) and R
2
(0.78, 0.79) during calibration and ENS
(0.68, 0.62) and R
2
(0.69, 0.63) during validation period respectively, which resulted in
moderately good model performance while simulating flow parameters in the catchments. It
was also shown from the model uncertainty analysis that the percentage of the simulated
data within the uncertainty bound is 78 % for Beressa and 73 % for Robigumer River which
are good representation of both catchments. The evaluation of surface water resource
availability flow forecasting was done for short term (2026-2050), medium term (2051-2075) and long term (2076-2100) future scenarios. The annual flow volume in Beressa
River increased by 47.8% and 54.5% in medium and long term future scenarios respectively
and decreased by -61.38% in the short term. Robigumer river flow volume showed annual
flow volume increases by 13.5% and 4.7% in the medium and long term period respectively,
and decrease by -24.4% for the short term period. The increase in flow volume will have a
paramount importance for agricultural activities practiced by local farmers; therefore any
effect on this river is reflected the decrease in flow will directly affect the ongoing water
resource developments planned and socio economic development on the area.
