A large set of biophysical system-modelling simulations were undertaken for a set of 30 representative farm systems across the Australian wheat belt for a historical period (1980-2010) and projected climate to 2030 (AR4). Simulated yield and gross margins were upscaled to national scale using a sample survey multi-purpose weighting method. Estimates for the baseline were validated using ABARES survey data and bias correction factors were applied to adjust all the simulation results.

We estimated a potential increase in the wheat belt yield (gap) of up to 19% compared to current yields (15.4 MT/year averaged over 1980-2010) by adjustments to the planting dates, cultivars, and fertiliser input (nitrogen). A 10% to 19% decline in wheat yield and gross margins is projected by 2030 without enhancement in efficiency of current systems (excluding the effect of elevated atmospheric CO₂). By 2030, the yield gap will be 25% without improvement in current efficiency. We predicted a 6% decline in yield at the efficiency frontier (excluding the effect of elevated CO₂) for 2030, due to the interactive effects of climate change. However, some further benefit from elevated CO₂ can be expected.

Closing the entire current yield gap is not expected, and this will remain as a future challenge. In addition, changes in climate and an increase in its variability will potentially make it more difficult to fill the yield gap. It will be essential to improve system efficiencies by about +11% to sustain production in 2030 at the average levels of the last 30 years.