Impacts of ENSO on Australian rainfall: what not to expect
Carly R. Tozer
A * , James S. Risbey A , Didier P. Monselesan A , Mike J. Pook A , Damien Irving A , Nandini Ramesh B , Jyoteeshkumar Reddy A and Dougal T. Squire A
A CSIRO, Environment, Hobart, Tas., Australia.
B CSIRO, Data61, Sydney, NSW, Australia.
Journal of Southern Hemisphere Earth Systems Science 73(1) 77-81 https://doi.org/10.1071/ES22034
Submitted: 12 October 2022 Accepted: 27 February 2023 Published: 22 March 2023
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the Bureau of Meteorology. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)
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.
Keywords: Australian climate, Australian rainfall, climate extreme, drought, dry, El Niño, ENSO, extreme probability, flood, La Niña, rainfall extremes, wet.
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