Spatiotemporal changes in wheat phenology, yield and water use efficiency under the CMIP5 multimodel ensemble projections in eastern Australia

The New South Wales (NSW) wheat belt is one of the most important regions for winter crops in Australia; however, its agricultural system is significantly affected by water stress and ongoing climate change. Statistically downscaled scenarios from 13 selected global climate models with RCP4.5 and RCP8.5 scenarios were combined with crop simulation models to simulate wheat productivity and water use. We projected that multi-model median yields could increase by 0.2% for RCP4.5 and 9.0% for RCP8.5 by 2061-2100. Although RCP4.5 showed a small decrease in median yield in the dry southwestern parts of the wheat belt, the higher CO2 concentration in RCP8.5 compensated some of the negative effects, resulting in 12.6% yield increase. Our results show that drier areas would benefit more from elevated CO2 than would the wetter areas. Without the increase in CO2 concentration, wheat yields decrease rapidly under RCP4.5 by 2061-2100 and much more so under RCP8.5 compared to the present. A decline in growing season length and a decrease in rainfall resulted in reduced crop water consumption. As a consequence, simulated evapotranspiration decreased by 10.2% for RCP4.5 and 16.9% for RCP8.5 across the NSW wheat belt. Increasing yields combined with decreasing evapotranspiration resulted in a simulated increase in water use efficiency by 9.9% for RCP4.5 and 29.7% for RCP8.5. Wheat production in water-limited, low-yielding environments appears to be less negatively impacted or in some cases even positively affected under future climate and CO2 changes, compared to other growing environments in the world.