Although the call was not made today...  we still need to prepare and plan as we’re highly confident that thresholds WILL be crossed, for an El Niño to be declared.

Secondly, we ALSO know, with high levels of confidence, that the Austral summer will be another record breaker and deliver significant threats.

ALL Australians need to start their preparations right now.

Previous deep El Niños have wrought devastation upon Australia. This summer could well be Australia’s hottest yet.

Translating the 2023 intercontinental heat waves across the northern hemisphere to an Australian summer should provide the impetus for all of us, ALL local councils, ALL businesses, ALL institutions, ALL recreational organizations, and ALL governments to prepare for hot summer.

We need to recall the hottest day we’ve experienced to date and extrapolate that to hotter, and longer lasting, and then recall what we need to do to survive and stay healthy. Temperatures in the high 30’s, 40’s and even high 40’s are very possible, and some regions may even reach 50°C. These temperatures exceed the human body’s natural cooling mechanism. Muscular movement generates body heat and exacerbates the risk of hyperthermia. Physical exercise in extreme heat can readily become lethal. Even resting in the extreme heat is hazardous for people with health conditions.

Early planning is vital to saving lives. We need Fire Plans, AND Heat Plans. To protect ourselves and our families, we need to devise strategies to stay cool, to keep our buildings cool, our pets cool and hydrated. Those with responsibilities for others, for employees, for people less fortunate, for pets, stock and wildlife, need to devise and test heat protective strategies that can endure for multi-day heat waves. Dependance on refrigeration and air conditioning is risky when extreme heat produces power outages. Cool water offers a back-up plan to cooling the body and preventing hyperthermia.

Drought resilience is clearly a critical attribute for communities globally, but particularly so for countries like Australia where so many of our rural centres and centres of critical agriculture are found in drought prone areas.

The declaration of an El Nino is not a matter of IF but rather WHEN for us year on year.

Unlike other types of natural disasters, that are sudden and highly impactful, drought is particularly devastating because of its long term ‘slow burn’ effects that can be experienced for years rather than weeks and months leading potentially to the long term erosion of social cohesion in our communities and mental and physical health crises - in addition to economic ruin.

Whilst much has been done, and continues to be done, with respect to research related to impacts at the farm gate, less has been quantified on the impact of drought and its many tentacles of impact on social structures and the long-term viability of our critical farming-based communities with flow on impacts to exports and our own standards of living. This is a critical gap in our current understanding of the impacts of drought on our Australian culture and way of life.

The Bureau continues to be cautious as to calling an El Niño, while some of the other international weather services have made more definitive judgements. The Bureau’s caution is appropriate. While El Niño and La Niña events are primarily understood to be associated with the nature of atmosphere-ocean interactions in the Tropics, there is mounting evidence that precursors to these events can be found in the middle- and high-latitude of the Southern Hemisphere. Research being undertaken at many institutions, including our group at The University of Melbourne, shows that the level of frontal and cyclone activity in the midlatitudes lead changes in the tropical circulations. The behaviour of the high latitude ‘Southern Annular Mode’ and ‘Semiannual Oscillation’ similarly impact on tropical evolution.

At present many of the tropical conditions point to a coming El Niño, this is far less clear for the harbingers that we use in the broad southern regions outside the Tropics. So ‘not all the planets are aligned’ at this stage, and the Bureau’s restraint would seem to be the best advice at this time.

The tropical Pacific has been warming in the past couple of months with an emerging El Niño signature, but the atmosphere has been slower to respond to the ocean warming. The atmospheric pressure difference between the central and west Pacific is one of the key metrics used to monitor the coupled response between the atmosphere and ocean during El Niño events. In the past few weeks, this metric has shifted back and forth. The bureau not declaring an El Niño today means that we are still waiting for the atmosphere to respond to the ocean warming. El Niño is generally associated with below-average rainfall and increased chances of droughts and heatwaves over east/southeast Australia.

Each national weather service has its own criteria for declaring El Niño (or La Niña) events, based on key factors physically associated with the impacts of these events on weather there – particularly rainfall. The BoM uses four inter-related indicators, three of which have met El Niño thresholds. But the Southern Oscillation Index (SOI), although it has been negative in several individual recent months, has not been consistently negative to the extent required to indicate an El Niño. In 2023 this could be linked to above-average sea surface temperatures around north-eastern Australia (note current concern about Great Barrier Reef SSTs); this anomaly is likely related to ongoing ocean warming due to global heating.

Similar inconclusive behaviour of the SOI occurred in the 1930s, early and late 1940s, 1978-1981 and 1984-1986 (among others), when no El Niño event developed. It is possible that the apparently developing 2023 El Niño event may fizzle out. Whether it does or not, it remains highly likely that spring and summer temperatures will be above average across eastern and south-eastern Australia, and the scales are weighted towards a drier spring/summer than has been our recent experience. These conditions are cause for concern regarding the coming bushfire season in the east, south and south-east (which could start earlier than usual), where recent wetter years have contributed to considerable vegetation growth and a potentially dangerous fuel load in hot dry weather.

Even though the BoM has not yet declared an El Nino it is very likely to be called in the coming weeks when the atmosphere and ocean become fully coupled. Ocean thresholds have already been reached but the atmosphere is responding only slowly. Sea-surface temperatures (SSTs) off the northwest coast of Australia have decreased to mostly neutral but they are still anomalously high in the tropics northeast of the continent. A sign of increased coupling to the atmosphere will be if they decrease to anonymously below average in both areas around tropical Australia.

The declaration of an El Niño would mean spring and summer rainfall in eastern Australia should be mostly less than average, and in some areas, likely well below average.

Extreme maximum temperatures would likely to occur, particularly through inland northeast Australia where, clear skies would aid daytime evaporation from both the land surface and vegetation.

That will increase the bushfire danger, particularly moving through spring into summer, because of the large amount of grassland produced inland from the recent La Niña phase rainfall.

The IOD will not help with rainfall through spring because it is currently neutral with the prospect of moving to a positive phase.

It will be interesting to track the state of the Southern Annular Mode. Periods of negative SAM are conducive to dry, warm westerly winds affecting the east coast thereby leading to extreme coastal maximum temperatures. The SAM typically varies on time scales of a few weeks but has trended positive in summers during recent decades. That implies humid onshore breezes increasing the discomfort factor which is dangerous for human health.