Looking beyond El Niño & La Niña to better understand Australia’s changing rainfall

The El Niño–Southern Oscillation (ENSO) is one of the strongest drivers of Australia’s seasonal rainfall. But even when a clear El Niño or La Niña is declared, there’s no guarantee that very dry or wet weather will follow. 

Australia’s rainfall is highly unpredictable. The chance of experiencing rain in any region depends on many connected environmental factors, from global ocean temperatures to small-scale weather systems affecting isolated areas.  

A major mode of climate variability, ENSO explains the changing patterns in winds and sea surface temperatures along the equatorial Pacific. These patterns shift between a warmer El Niño phase, and a colder La Niña phase, cycling around every three to seven years.

For Australia, El Niño and La Niña events are closely related to spring and summer rainfall. Typically, La Niña increases the likelihood of wetter conditions and a higher risk of flooding across Australia, while El Niño often produces drier conditions with a larger chance of experiencing droughts.

However, actual rainfall over spring-summer does not always align with these expectations. The 2020 La Niña event for example, produced average to below-average rainfall for most of Australia, and more recently during the 2023 El Niño event, Eastern Australia experienced average to above-average rainfall during the spring season, brought on by a particularly wet November. These outcomes have challenged public expectations around El Niño and La Niña forecasting, and highlight an essential point: El Niño-Southern Oscillation, while influential, does not guarantee specific rainfall trends and patterns.

It’s important that forecasts, media and climate experts acknowledge the importance of other factors influencing rainfall. Climate influences such as the Indian Ocean Dipole, the Southern Annular Mode, and even small-scale weather systems, all interact in ways that can enhance or suppress El Niño and La Niña influences. Communicating rainfall expectations relying solely on El Niño or La Niña impacts can be misleading and have potentially costly impacts for communities and industries.

That’s why the ARC Centre of Excellence for 21st Century Weather is continuing to develop and communicate the understanding of how El Niño and La Niña interact with other climate drivers and weather systems, shaping Australia’s rainfall. Research has shown that many different interactions between the ocean, atmosphere and land can influence rainfall totals from year to year. This suggests that no single climate variable, while strong, will solely drive our rainfall expectations over Australia.

While El Niño and La Niña are useful in helping forecast rainfall across Australia during spring and summer, we must be cautious in how we communicate their expected impacts. Australia’s climate is complex, and communicating this complexity is key in improving how we plan for high-impact weather such as floods, droughts and everything in between.

By Keilani Trewavis, Honours student, ARC Centre of Excellence for 21st Century Weather, Monash University.