What Drives Interannual Rainfall Variability Over Northern Australia?

Abstract

The interannual variability of northern Australian (NA) rainfall is caused by local processes as well as remote teleconnections, many of them being interrelated. Their influence evolves throughout the wet season, from October through April. Using a stepwise linear regression and examining individual months, we identify the key drivers for rainfall variability over northwest and northeast Australia. Our research shows that the El Niño-Southern Oscillation (ENSO), followed by local sea surface temperatures (SSTs), are the key sources of rainfall variability in October and November. More specifically, the Arafura and Coral Sea SSTs contribute to rainfall variability over northwest Australia, while the Coral Sea SSTs strongly impact on northeast Australian rainfall during these months. The combined ENSO and local SST indices explain up to 50% of variance in observed NA spring monthly mean rainfall. However, the SST influence from both seas breaks down with the onset of the Australian summer monsoon in late December, and by January, SST indices explain zero variance in rainfall. Instead, December to March rainfall variability is associated with a wind-evaporation feedback, which is particularly strong over northwest Australia. The evaporation index is the only predictor that we investigated that can explain any variance in northwest Australian rainfall in January. While the more purely monsoonal northwest of Australia is dominated by variability internal to the monsoon system, rainfall variability in the northeast retains some influence from remote climate drivers throughout the monsoon season. Further research is needed to clarify the processes and timescale involved in the wind-evaporation feedback.