May 26, 2026
Rainfall is shaped by a complex systems of interacting influences like ocean cycles, atmospheric circulation, and broader climate change. While scientists understand many of the key drivers, ongoing research is needed to uncover new factors and refine how these moving parts influence when and where the rain falls. It is this work that directly feeds into improving forecasts and ensures the best possible information is available to decision-makers and the public.
In spring 2022, southeastern Australia received a significant amount of rainfall, bringing severe flooding that affected communities, infrastructure, agriculture and ecosystems across the region. For many people in this region, the impacts were immediate and costly. But behind those impacts sits an important scientific question: why was it that wet, and how well was it foreseeable?
Previous research from the NESP Climate Systems Hub has shown that large-scale climate drivers can set the stage for persistently wet conditions across eastern Australia, particularly during winter and spring. Well-known climate drivers like La Niña, the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM) strongly influence how much moisture reaches our continent and where it rains.
Building on this earlier work, this latest study took a closer look at the extreme rainfall of Spring 2022. Instead of asking only which climate drivers were present, we asked a more detailed and decision relevant question: can the scale of the rainfall be explained by known climate drivers and human-caused climate change alone? And how predictable was its extreme nature?
Using a combination of statistical analysis and Australia’s state-of-the-art dynamical seasonal forecast system, ACCESS-S2, we found that the answer is both reassuring and challenging. Together, the convergence of climate drivers – a multiyear La Niña, a negative IOD, and a strongly positive SAM – combined with long-term greenhouse gas warming, did explain a substantial part of the unusually wet conditions.
But crucially, these factors did not explain the full magnitude of the event.
What pushed Spring 2022 into record-breaking territory was the behaviour of the atmosphere itself. Unusual large-scale pressure patterns enhanced the transport of moisture towards southeastern Australia. Winds at 15–50 km altitudes were much stronger than their average speeds, and rain-bearing weather systems were more frequent and produced heavier rainfall. In other words, the tropical ocean conditions loaded the dice, but the unusual atmospheric dynamics rolled them in a way that amplified the rainfall.
This distinction matters for decision makers. This work shows that atmospheric dynamics can greatly amplify outcomes, limiting how precisely we can predict exactly how extreme an event may become. That knowledge needs to be built into planning, risk assessment and emergency preparedness, for example by stress-testing decisions against a wider range of plausible rainfall scenarios rather than relying on a single ‘most likely’ outcome.
Importantly, this research extends earlier Hub findings by showing that while multi-year La Niña events raise the likelihood of higher-than-average rainfall, the most damaging rainfall extremes can depend on how oceans, atmosphere, and long-term human-induced global warming interact in real time. The results point to the potential benefit of incorporating real-time ozone forcing in seasonal forecasting systems to better capture atmospheric variability and improve forecast skill. It also highlights why continued investigation and research of past events is essential. By better understanding these interactions – and where predictability breaks down – we improve our ability to anticipate risk, stress-test decisions, and prepare for a future with further changes to extreme rainfall.
This is ongoing work, and each new event helps refine our understanding. By continuing to investigate why events like Spring 2022 unfold, we strengthen the evidence base that decision makers rely on to plan for what the future may bring.
