An interpretation of Australian rainfall projections

Abstract

The majority of climate models project a winter rainfall reduction over south-eastern Australia (SEA), while some show a tendency for a summer rainfall increase. The dynamics for these rainfall changes are not clear. Using outputs from a climate model, we show that a summer rainfall increase is consistent with a large Tasman Sea warming promoting convection, and an upward trend of the Southern Annular Mode (SAM) promoting onshore flows; these processes dominate over a rainfall decrease from an El Nino-like warming pattern. In winter, similar effects from a Tasman Sea warming and an upward SAM trend operate along Australia’s east coast, however, the rain-reducing impact of an Indian Ocean Dipole-like warming pattern dominates. In both seasons, the upward SAM trend causes a rainfall reduction over southern Australia. Summer rainfall over north-western Australia is projected to decrease, due to an unrealistic relationship with the El Nino- Southern Oscillation. Possible uncertainties are discussed.