IMPACTS OF CLIMATE CHANGE ON WATER BALANCE COMPONENTS AND IRRIGATION WATER REQUIREMENTS USING CMIP6 SCENARIOS IN UPPER WABE SUB-BASIN, WABE SHEBELE RIVER BASIN, ETHIOPIA

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.