For much of eastern Australia, summer has so far been marked by that have battered parts of Queensland and Victoria.
After three consecutive years of La Niña summers, the Bureau of Meteorology's that an El Niño event was underway brought expectations of hotter and drier conditions through spring and summer.
But climate scientists say common understandings of El Niño can sometimes be "overly simplistic" and the weather event is just one of the drivers of the country's weather and climate.
With the El Niño event continuing, what can we expect for the remaining summer months?
What was the weather bureau's outlook for spring and summer?
Last September, Australia's weather bureau formally declared both in the Pacific Ocean, to the country's east, and a to the west.
El Niño events occur when sea surface temperatures in the central and eastern tropical Pacific are warmer than usual, while La Niña events are characterised by cooler-than-usual waters.
These changes in the Pacific and overlying atmosphere form part of a cycle called the El Niño-Southern Oscillation (ENSO).
The IOD refers to changes in the difference between sea temperatures of the western and eastern Indian Ocean.
Zoe Gillett, a climate scientist from the ARC Centre of Excellence for Climate Extremes at the University of NSW, said El Niño events typically reduce the chance of spring rain in eastern Australia and increase the likelihood of warm days.
"A positive IOD tends to decrease the chance of spring rain in central and southeastern Australia," she said. "When El Niño and the positive IOD co-occur, drying in Australia is typically amplified."
Under the influence of these two drivers, the bureau's outlook indicated warmer and drier conditions would be more likely over spring (September to November) and summer (December to February) for parts of Australia.
When asked about the prospect of a hot summer during a press conference, the bureau's manager of climate services, Karl Braganza, said: "In all likelihood, we can expect that this summer will be hotter than average and certainly hotter than the last three years."
In a January 2024 statement, a bureau spokesperson said its long-range forecast for spring had indicated both the development of a positive IOD and El Niño event, along with below-median rainfall for large areas of the country, and warmer day and night-time temperatures.
"The bureau's long-range forecasts for summer indicated neutral to increased likelihood of above-average rainfall across much of the continent for December and January, and increased likelihood of below-average rainfall for the northern tropics," the spokesperson said.
What happened? What about all the recent rain?
Looking back to early spring last year, experts say the forecasts indeed came to pass.
According to bureau data, August to October was the driest such period on record for Australia, with very warm temperatures. Last September was the driest September on record and the second-driest month ever on record.
The impacts of this dry start to spring saw extensive fires across the country's north, including parts of Western Australia, the Northern Territory and Queensland.
"Heavy rainfall events and persistent humid conditions were experienced across eastern Australia following the record dry start to spring," the bureau spokesperson said.
Andrew King is a senior lecturer in climate science at the ARC Centre of Excellence for Climate Extremes and the University of Melbourne. He said spring conditions aligned with the bureau's outlook.
“Overall, it was slightly drier than normal. It was only towards the end of spring that it really became wetter."
A house is flooded following heavy rainfall north of Bendigo in January this year. Source: AAP / Diego Fedele
Are El Niño events always hot and dry?
King said El Niño events tend to be associated with drier and warmer conditions, particularly in eastern Australia, and more so in spring than in summer.
"It's in spring that we see the strongest response of Australia's climate to climate drivers generally — both in the Pacific through El Niño and La Niña, but also in the Indian Ocean," he said.
He said El Niño events "are less reliably dry than La Niñas are reliably wet".
"If we have a La Niña, we can be quite confident we're going to have a wet spring and a wet summer. With El Niño, we have less confidence in the other direction — that it will be drier than normal," he said.
In its latest update on 9 January, the bureau said the typical drying influence of El Niño usually reduces during summer, especially in the east. However, below-median rainfall is still often observed in the northeast.
King believes there's a widely held "overly simplistic" idea of what El Niño events mean for Australian weather.
"Many Australians do think of El Niño meaning hot, dry conditions. It just increases the probability of having warmer and drier conditions — and more so in spring than in summer," he said.
Gillett agreed.
"This serves as an important reminder that having an El Niño and a positive IOD does not guarantee that eastern Australia will be hot and dry, rather they increase the likelihood of hotter and drier conditions," she said.
The bureau said in its 9 January update: "As we have seen this year and in the historical data, high-impact rainfall events can occur during El Niño years, particularly during October to April when severe storm frequency peaks."
Its spokesperson previously said no two El Niño and IOD events are the same, and their impact on Australia varies. This is particularly true in the summer months.
They said the widespread and regular rainfall across southeastern Australia across multiple months is "unusual for El Niño".
The other climate drivers influencing conditions this summer
Experts say El Niño is just one of the drivers of the country's weather and climate.
King said the recent rainfall is in part due to the relatively warm sea surface temperatures in the Tasman Sea, to the east of Australia.
"We have what is called a positive Southern Annular Mode (SAM) which means we have more winds from the east crossing the east coast of Australia, and that promotes wetter than normal conditions as well," he said.
"We have a lot of things that affect Australia's climate — and it means it's never quite as simple as El Niño is dry, La Niña is wet. There's always other factors that complicate things."
The bureau spokesperson also noted the presence of a positive SAM combined with very high temperatures in the Tasman Sea "likely contributed to rainfall events in eastern Australia in December and January".
"It is unusual to see a persistently positive SAM during El Niño, as that is more typical during a La Niña phase," they said.
Australia heats up with eighth-warmest year on record
Meanwhile, frequent low-to-severe intensity heatwave conditions had parts of northern and central Australia sweltering from October to December last year.
, matching a global pattern of extreme weather and the Earth's hottest year on record.
The temperature came in 0.98C warmer than the 1961-1990 average to mark the nation's eighth-warmest year on record, according to the bureau's annual climate summary published last week.
"It has been a bit of a weird summer so far," King said.
"We have seen lots of rain in the east, but we have also seen these heatwaves. It shows that in Australia, we get all kinds of extreme weather and it’s quite fickle — it can switch quite quickly.
"It's worth noting that, as we're warming the planet, we're also seeing more frequent, more intense heatwaves. So these extreme temperatures we see during heatwaves are getting a bit worse than they would if we weren't emitting greenhouse gases."
What's the outlook for the rest of summer?
According to the bureau's latest update, the El Niño event continues in the tropical Pacific. Model forecasts indicate the warmth of sea surface temperatures is "likely at or near its peak".
They're expected to remain above El Niño thresholds into the southern hemisphere autumn this year.
The bureau's long-range forecast, issued on 4 January this year, indicates increased rainfall in southeastern Australia and drier conditions in north and western Australia from January through to March.
"Warmer days and nights are likely for the rest of the summer months," Gillett said.
"The bureau will continue to update the community as new observations of the ocean, land surface and atmosphere are incorporated into our forecast systems," its spokesperson said.
