Assessment of climate change impacts on crop and irrigation water demand in the Awash River basin of Ethiopia using CMIP6 models

Abstract Irrigation water is crucial for global food security, but it is increasingly vulnerable to climate change. Accurate projections of irrigation water demand under climate change scenarios are essential for water resource planning in an area like the Awash basin, where water is scarce. 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. CMIP6 climate projections were bias-corrected and used to estimate reference evapotranspiration (ETo) and future crop water demand. 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, decreasing in a few stations and increasing in the majority of the stations, especially during 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% due to varying levels of climate change impact for different seasons and annual periods. 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 provides a comprehensive assessment of crop and irrigation water demand in the basin using bias-corrected CMIP6 ensemble projections, offering better reliable estimates. The findings provide essential evidence to guide agricultural policies and practices toward climate-resilient irrigation planning, crop selection, and water allocation in the Awash River Basin. Moreover, the study underscores the need for adaptive irrigation strategies, such as precision agriculture, water-saving technologies, crop calendar adjustment, and water storage infrastructure, to ensure sustainable water management in the basin.