Australian precipitation is strongly affected by ocean-atmosphere modes of variability, such as the El Niño – Southern Oscillation (ENSO), and by internal atmospheric modes, e.g. the Southern Annular Mode (SAM). In this study we investigate the contribution of the sea surface temperature (SST) interannual to multidecadal variability for Australian precipitation, and examine to what extent internal atmospheric variability can generate extended periods of drought. Multi-century simulations are integrated using the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) model. Three experiments are performed: (i) a fully coupled climate system run, (ii) a run forced with a climatological cycle of SST, i.e. no SST variability beyond one year, and (iii) a run forced with monthly and inter annually varying SST, i.e. containing SST variability but no air-sea feedback.

Results show that year-to-year variations in SST enhance rainfall variability and extremes, thus generating more severe droughts and wet spells compared to a world without interannual ocean variations. We also found that ENSO is a crucial phenomenon for resetting droughts and pluvials. In the fully-coupled climate system simulation, dry and wet spells are more likely to have a 3-yr duration. However, in the absence of ocean variability (i.e. in a world with no ENSO) droughts and pluvials generated by internal atmosphere variability can last longer, as there is no ENSO event to terminate extended dry or wet periods.