Abstract:
Climate predictions using recent and high-resolution climate models are becoming important for
effective decision-making and for designing appropriate climate change adaptation and mitigation
strategies. Understanding climate change impacts on water balance components and irrigation
water requirements is critical to assessing future crop performance and developing sustainable
adaptation strategies. This paper presents the impacts of climate change on water balance
components and irrigation water requirements using CMIP6 scenarios in the Upper Wabe Sub basin, Wabe Shebele River Basin, Ethiopia. The Soil and Water Assessment Tool (SWAT) models
were used to apply climate change signals under the Shared Socioeconomic Pathways (SSPs)
intermediate (SSP4.5) and high (SSP8.5) scenarios. For the baseline scenario, the period 1985–
2014 was employed, whereas the periods 2040s (2025–2054) and 2070s (2055–2084), or near and
mid-terms, respectively, were used for future climate prediction. The distribution mapping bias
correction method and percentage of bias (PBIAS), Pearson correlation coefficient (r), mean
absolute error (MAE), root mean square error (RMSE), mean bias error (MBE), and volumetric
efficiency (VE) statistical indices were used to evaluate the BCC-CSM2-MR and MRI-ESM2-0
Global Circulation Models (GCMs) simulation outputs. To quantify the effect of climate change
on irrigation water requirements, dominant crops in the sub-basin were used. The results showed
that mean annual and seasonal precipitation and maximum and minimum temperatures were
higher than the baseline. The SWAT model performed well during calibration and validation, and
future components of the water balance were increased from the baseline. Future increases in
temperatures and decreasing precipitation variability, as well as potential evapotranspiration, are
expected to increase irrigation water requirements across the sub-basin. These results show how
water balance components altered by climate change can benefit from high-resolution future
scenarios. Finally, this study will help Wabe Shebelle River Basin planners, policymakers, and
water resources managers develop adaptation strategies to mitigate the effects of climate change.
