The current projections for future change in Australian rainfall are based on climate model simulations contributed to the CMIP5 international experiment. The wide range of possible changes in rainfall from the models, both increases and decreases, poses a major research challenge. It is known that part of the variation in simulated rainfall change is associated with the horizontal transport of tropical moisture into the mid-latitudes, but suitable data for analysis were not available from CMIP5.
The new CMIP6 archive includes vertically-integrated moisture flux data, submitted by an ensemble of models that will include ACCESS-CM2 and ACCESS-ESM1.5. We assess these fluxes, the atmospheric moisture budget, and rainfall for the present climate and climates under rising CO2 concentrations. Preliminary results indicate that the future change in the convergence of the flux is highly spatially correlated with the precipitation change. Using the available results, prototype probabilistic projections of the change in these variables will be developed. The potential for some constraint on possible future Australian rainfall based on the new analyses will be considered. This would have a considerable benefit to users of such projections.