Climate Change Impacts on Crop and Irrigation Water Demand: Insights from CMIP6 Models in the Awash River Basin, Ethiopia

Irrigation water is crucial for global food security, but it is increasingly vulnerable to climate change. This study utilizes Coupled Model Intercomparison Project Phase 6 (CMIP6) General Circulation Models (GCMs) to project future crop and irrigation water demand under two shared socioeconomic pathways (SSP2-4.5 and SSP5-8.5) for the 2030s, 2050s, and 2080s in the Awash River Basin. The ensemble model outputs were used after bias correction to calculate reference evapotranspiration (ETo) in the basin, followed by projecting crop and irrigation water demand for selected stations. This study demonstrated an improved simulation of climate variables using the ensemble model compared to individual models. The linear scaling bias correction method outperformed for rainfall and minimum temperature, while variance scaling and distribution mapping were more effective for maximum temperature in the basin. Maximum temperature increased by 0.5, 1.2, and 1.6°C under SSP2-4.5, and 0.6, 1.6, and 2.8°C under SSP5-8.5, for the 2030s, 2050s, and 2080s, respectively, compared to the baseline period. The minimum temperature increased by 0.8, 1.5, and 2.0°C under SSP2-4.5, and 1.0, 2.2, and 3.6°C under SSP5-8.5, for the same periods. Precipitation showed a spatial heterogeneity that ranges from a decrease of 13.8% to an increase in most stations reaching 175% at Dubti by the 2080s under SSP5-8.5. ETo generally increased, ranging from a 2.1% decrease to a 22.6% increase. Most crops showed increased crop and irrigation water demands, except wheat, which experienced reductions of up to 5.0% in crop water demand and 15.6% in irrigation demand which is associated with seasonal shifts. Maize, tomato, onion, tropical fruits, and sugarcane exhibited varying increases in water demand, ranging from 1.7 to 13.3%. However, irrigation water demand fluctuates between a 4.6% decrease and a 9.0% increase under different climate change scenarios revealing a growing pressure on water resources. This study underscores the critical need for adaptive irrigation strategies, such as precision agriculture, water-saving technologies, crop calendar adjustment, and water storage infrastructure, to ensure sustainable water management and climate change resilience in the basin for policy shifts.