The 19 months of wet weather has primarily been driven by two large-scale weather systems originating in the oceans on either side of Australia, says Nina Kidder at the University of New South Wales in Sydney. One is La Niña – a weather system arising in the Pacific Ocean that brings rain to Australia’s east coast. A rare grouping of three La Niña cycles in a row since late 2020 has meant “basically no stop in the wet conditions,” says Ridder. The other is a weather system called the Indian Ocean Dipole, which occurs in the Indian Ocean and is currently in its negative phase, which brings more rain to south-eastern Australia.