As the run of La Nina events gives way to a likely El Nino period, Australia could be in for a hot, dry summer

By Andy Swales

After three consecutive La Nina events, and the devastating floods they helped bring on, Australians could be forgiven for thinking they are due a break from exotic-sounding weather phenomena.

No such luck. In June, the Bureau of Meteorology announced an El Nino alert, signifying a 70% chance that “the girl” (La Nina) is making way for “the boy”.

Coupled with a likely positive Indian Ocean Dipole, it points to a hotter, drier summer for much of the country.

At time of writing, that alert level remains unchanged. But in early July the World Meteorological Organisation (WMO) had seen enough, declaring the onset of El Nino conditions, “setting the stage for a likely surge in global temperatures and disruptive weather and climate patterns”.

It says the event will be of at least moderate strength and, coupled with the effects of climate change, could – between this year and 2027 – temporarily push annual average global temperatures above the 1.5-degree warming target set in the Paris Climate Agreement.

“The onset of El Nino will greatly increase the likelihood of breaking temperature records and triggering more extreme heat in many parts of the world and in the ocean,” WMO Secretary-General Petteri Taalas says.

Bureau of Meteorology Senior Climatologist Simon Grainger told Insurance News his organisation’s long-range forecasts are in line with its outlook for the El Nino Southern  Oscillation (ENSO) – the term used to describe the shifts between the El Nino phase and the La Nina phase, the latter of which is typically associated with increased rainfall in Australia.

“Our long-range forecasts are showing it’s likely to be drier than average for…July to September for the south-west and south-east of Australia [and] also much of eastern Australia,” he says.

“Longer term, with El Nino conditions it’s typically drier than usual during winter and spring across eastern Australia. Our ENSO outlook is reflected in our long-range forecasts.”

El Nino phases tend to occur every three to eight years (the last one was in 2015-2016), typically along an autumn-to-autumn period of rise and decline.

They rise when the Trade Winds weaken and the central and eastern tropical Pacific warms, triggering a shift in cloudiness and rainfall from the western to the central tropical Pacific. The Indian Ocean Dipole represents the difference in sea surface temperatures in the eastern and western tropical Indian Ocean.

A negative phase tends to bring above average winter-spring rainfall in Australia, while a positive phase brings drier than average seasons.

The bureau says the impacts of the coming El Nino could include reduced rainfall for eastern Australia; higher daytime temperatures for the southern two-thirds of Australia; increased risk of extreme heat; increased bushfire danger in the south-east; increased frost risk under clear night skies; lower alpine snow depths; a later start to the northern wet season; and reduced tropical cyclone numbers.

The spectre of bushfires is likely to haunt many communities, particularly after the horrifying blazes of 2019-20’s Black Summer. But CSIRO Chief Research Scientist Pep Canadell suggests the wet La Nina years may at least spare our forests.

“Depending on where drought hits the most during this coming El Nino, we could have a big fire season in the grass-dominated rangelands in large parts of the continent and savannahs of the north, where the build-up of grass biomass over the past three wet years can quickly dry and become flammable to fire,” he says.

“In the eastern and southern parts of the country, open woodlands could be equally exposed to high fire risk, but we expect forests to continue to be wetter than average from La Nina years, making it less likely that fuels will be primed for a big forest fire season.”

CSIRO Leader for Bushfire Behaviour and Risks Andrew Sullivan says the problem may be exacerbated if we enter a run of consecutive El Ninos following the three La Ninas.

“If we face consecutive El Nino events and extended periods of decreased rainfall, then increased vegetation growth from recent years could become available bushfire fuel,” he says.

“Areas of open vegetation, such as agricultural lands, grasslands and woodlands, follow an annual burning cycle. The threat of bushfires will transition from these areas to forests, where multiple years of drying vegetation heighten the potential for increased fuel and potential for large intense fires if ignitions coincide with extreme fire weather events.”

However, the run of three La Ninas in a row does not mean we will have three El Ninos, with the latter tending to run to two years at most.

Dr Grainger says the Intergovernmental Panel on Climate Change’s latest report found no clear sign that global warming has affected or will affect the frequency of El Nino and La Nina events.

It could be affecting their severity, though. “What does seem to be fairly definitive is that the rainfall variability that’s caused by ENSO…it’s more likely that rainfall variability [could] increase, so any particular ENSO event could have a much more extreme response in terms of the rainfall.

“I think there’s reasonable agreement that what we’ve seen in the past probably 50 or so years is that the [rainfall] variability actually has increased. The largest El Nino events in recent records – 2015-16 would be the last big one –tended to be stronger than we’ve seen prior to about the 1970s.”

As far as the outlook for insurers goes, Aon reckons El Nino is preferable to La Nina.

In a catastrophe report in June, it noted that flooding is Australia’s second most costly peril since 1967, causing $23.53 billion of industry reported losses, just behind cyclones on $28.11 billion.

“After three years of back-to-back La Ninas, the concern is fuel growth and the pre-conditioning of the landscape for bushfire,” Aon senior analyst Tom Mortlock says.

“The historical loss record shows us that bushfire losses are correlated to periods of El Nino, albeit to a lesser extent than floods and cyclones are to La Nina.

“El Nino years have typically led to lower total insured loss years in Australia than La Nina years, and while floods and cyclones do occur during El Nino, they are less likely.”

While bushfires may not rack up the sort of insured losses wrought by wind and floods, they can still be devastating for the people, properties, flora and fauna affected. And there is another reason to hope we don’t see a repeat of the Black Summer.

Earlier this year, climate scientists at the US National Centre for Atmospheric Research released research suggesting the 2019-20 bushfires made an important contribution to the following string of La Nina events and consequent flooding.

The study, incorporating satellite data for bushfire smoke into model simulations, shows particulate emissions from the blazes brightened cloud decks across the southern hemisphere, especially near Peru, and the net result was a cooling of the tropical Pacific Ocean, where La Ninas form.

“Many people quickly forgot about the Australian fires, especially as the Covid pandemic exploded,” study lead author John Fasullo said.

“But the Earth system has a long memory, and the impacts of the fires lingered for years.”