How strongly are mean and extreme precipitation coupled?

Changes in mean and extreme precipitation are among the most important consequences of climate change. Here we examine the relationship between the mean and three different measures of extreme precipitation over the Australian continent, from a regional climate projection ensemble. We show that model uncertainty in mean and extreme precipitation are tightly coupled for both the present-day climate and future changes. On the continental scale the differences in mean precipitation explain 80-99% of the variance in the extremes. We also find that in most regions except along the coasts, precipitation statistics projected by regional modelling system (RCM) are highly predictable from the mean precipitation of the global model (GCM) providing the boundary conditions. In coastal regions RCMs are more accurate than GCMs and they also have more impact on present-day statistics, however, this impact disappears for future changes, suggesting that improved present-day accuracy will not carry over to future changes.