Impacts of ENSO on Australian rainfall: what not to expect
Carly R. Tozer, James S. Risbey, Didier P. Monselesan, Mike Pook, Damien Irving, Nandini Ramesh, Jyoteeshkumar Reddy, Dougal T. Squire
Abstract
In eastern Australia we expect to experience wet conditions during La Niña and dry during El Niño events. We explore how well these expectations match historical outcomes by assessing, for spring, how much rain fell during past La Niña and El Niño events. We use a tercile framing and find that for rainfall averaged across eastern Australia, La Niña approximately doubles the chance of spring rainfall being in the wet tercile whereas El Niño approximately doubles the chance of a dry spring. Also of note is that during La Niña, the dry tercile is mostly vacant and during El Niño, the wet tercile is mostly vacant, indicating that one should not expect dry conditions in La Niña or wet in El Niño for eastern Australia as a whole. At individual locations across Australia, the results vary, and in some cases, including the eastern seaboard, La Niña or El Niño events do not change the odds of wet and dry springs significantly beyond chance expectations. For example, in the Sydney region, the normal chance of experiencing a wet tercile spring is 33% and this increases only slightly in a La Niña to 38%, suggesting that La Niña is not a strong indicator for wet conditions in this region. These outcomes may help to manage our expectations for the likely rainfall outcomes during future El Niño–Southern Oscillation (ENSO) events.