What made eastern Australia so wet from 2020 to 2022?

From 2020 to 2022, eastern Australia had much more rain than usual. In these years, three La Niña events occurred in a row, only the third occurrence of a triple La Niña since the 1950s.  Widespread flooding across Queensland, New South Wales, Victoria and Tasmania led to significant damage, affecting communities, livelihoods, our natural environment and impacting multiple sectors such as transport, agriculture and infrastructure.

Climate drivers influence eastern Australia’s highly variable rainfall. La Niña, negative Indian Ocean Dipole (IOD), and positive Southern Annular Mode (SAM) phases typically promote more rainfall in spring, while El Niño, positive IOD, and negative SAM phases generally mean less rain and drier, warmer conditions in spring.

Each driver on its own can influence rainfall significantly, and when they co-occur, their impacts are further strengthened.

Under climate change, most models project a decline in winter-spring rainfall in southeastern Australia, and the influence of ENSO on rainfall is likely to strengthen. This would suggest increased drying during El Niño years but extreme La Niña-related rainfall may increase.