Integrated water resources management under climate change scenarios in the sub-basin of Abaya-Chamo, Ethiopia

Abstract

In this study, the impact of climate change on surface water availability and its allocation system was carried out within Bilate watershed in the Abaya-Chamo sub-basin of Rift Valley Lakes Basin in Ethiopia. Predicted rainfall and temperature time series data were obtained from regional climate outputs of Coordinated Regional Climate Downscaling Experiment (CORDEX)-Africa for the three representative concentration pathways (RCP) scenarios (RCP2.6, RCP4.5, and RCP8.5) for the four time periods (2015–2020, 2021–2025, 2026–2030 and 2031–2035). The result revealed that the future maximum and minimum temperature can be increased during all three scenarios. However, precipitation showed an increase or decreasing trend in future scenarios at different time scales. Further, SWAT model was calibrated and validated to simulate the future streamflow under RCP2.6 and RCP8.5 scenarios. WEAP model was employed for integrated water resources allocations under selected climate change scenarios. The SWAT model performance was found satisfactory during calibration [correlation coefficient (R2) = 0.77, Nash–Sutcliffe efficiency (NSE) = 0.755, percent deviation (D) = 2.558] and validation period (R2 = 0.798, NSE = 0.778, D= − 3.93). The model output shows that there may be an annual decrease in flow upto − 12.1 and − 16.21% for RCP2.6 and RCP8.5 scenarios. The annual surface water availability was found to be 570 million cubic meter (MCM) in the Bilate watershed for the current accounted year 2015. However, the current utilization of these resources is very limited about 51.49 MCM (9.03%) in the basin including domestic, livestock and minor agricultural activities. Furthermore, four scenarios were developed based on different set of assumptions in the basin up to 2035. It was estimated that total annual consumption will be around 14.53, 20.43, 37.47 and 44.46% for the reference, scenario one, two and three, respectively. This study also determines the environmental flow requirements (25% of the mean annual flow volume) to maintain the basic ecological functioning in the basin and regulate flow for downstream uses. This study was found that integrated water resources management strategy in the basin could utilize water resources potential effectively in the future. Therefore, this study is useful for the different stakeholders in the study region for the optimal allocation of water resources under climate change scenarios.