La Nina, which has been blamed for delivering heavy downpours to Australia’s east, is officially over. But as it fades, another climate driver can be seen on the radar and is set to influence the weather.
La Nina has finally left our space.
This climate driver that triggered the cool, wet summer across Australia has or is almost dissipating, according to the Bureau of Meteorology (BoM).
Its departure has happened a month earlier than forecast.
The once-in-a-century rainfall event that swamped NSW and some parts of Queensland causing three deaths has made its final push. It also brought about one of the calmest bushfire seasons in years.
However, the BOM has issued a warning that while La Nina may be on its way out, another climate driver could as well cause heavy downpours in coming months besides leading to increased tropical cyclones.
There are chances that the La Nina may make an encore appearance immediately after winter.
In their recent climate note, the weather Bureau noted that its El Nino—Southern Oscillation (ENSO) outlook changed from a La Nina to an inactive system. What this means is that climate drivers are currently in neutral—i.e. it’s neither an El Nino nor a La Nina.
Climate agencies in other countries provide varied definitions of La Nina with the USA meteorological service still having a La Nina—though coming months could see it come to an end.
The La Nina was declared in September 2020. While it wasn’t very strong then, it nonetheless caused some of the most destructive weather effects related to the climate driver in a decade.
Even though the numbers in the 2020-21 La Nina season are yet to be fully crunched, it’s possible that March could end up being one of the dampest on record in New South Wales.
“This rain event was beyond what we were expecting,” Dr Ailie Gallant from the Monash University Climate Change Communication Research Hub told stormassist.com.au
“Ten years ago, in 2011, was a very strong La Nina. But this La Nina was very middle of the road; it wasn’t super weak or super strong.”
La Nina leads to the calmest fire season in a decade
The NSW Rural Fire Service reported today that this was the calmest bushfire season since the strongest La Nina which occurred in 2010/11.
The state recorded only 11 days of total fire bans compared to 60 in 2020, Rob Rogers the RFS commissioner said.
“Firefighters have responded to just over 5500 bush and grass fires burning 30,963 hectares across NSW, considerably less than the 11,400 fires and 5.5 million hectares lost last season.”
According to experts, one of the drivers that could have turbocharged this year’s fairly moderate La Nina was the rapidly rising sea surface temperatures that are considered a major symptom of climate change.
Warmer waters evaporate into the atmosphere.
“A warmer atmosphere can hold more water vapour and scientists calculate that this can increase moisture in the atmosphere by approximately 7 per cent per degree of global warming,” said Dr Gallant.
What has changed for La Nina to end?
During the cooling process of the ENSO, a La Nina fizzes up when strong winds are thrust from the east to the west across the Pacific ocean which moves cooler water upwards from the depths of the eastern and central equatorial ocean.
Thereafter, the winds push back warmer waters off Australia’s coast and closer to the continent, potentially bringing more moisture.
However, that has since changed, according to the BOM.
“Tropical Pacific Ocean sea surface temperatures have persisted at ENSO-neutral values for several weeks. Below the surface, much of the tropical Pacific is now at near average temperatures.”
In most cases, La Nina events fade away in autumn though the forecast indicated that it would linger on until May, albeit in a weakened form.
Another climate driver emerging
The weather bureau said that the ENSO could possibly remain in neutral state at least up to the end of winter. Neutral means fairly average weather conditions throughout eastern Australia.
But, with La Nina exiting, the presence of another climate driver is evident—the Madden-Julian Oscillation (MJO).
The MJO is basically a piece of cloud that surrounds the globe at the equator and this includes over the northern Australia.
When it crosses over, rainfall can increase. Its effects are particularly felt from October to April when the Top End wet season is fully in. When its arrival in Australia is combined with a monsoon trough—a merger currently taking place, it leads to heavier falls and more cyclones.
Apparently, a tropical cyclone is possible in coming days within the Indian Ocean near north western WA.
“The MJO has moved into the Australian region at moderate strength and is expected to bring increased cloudiness and rainfall to far northern Australia and the broader continent over the next week or two,” explained the BOM.
Despite the fact that La Nina is coming to an end, the rainfall might not. The more heavy falls could shift further south in April.
La Nina likely to return
Forecasts show that this La Nina could reappear though its return may not have a greater impact as the original.
“There is a higher likelihood of having back-to-back La Ninas than a transition from a La Nina to an El Nino,” Monash University climate scientist Dr Shayne McGregor told stormassist.com.au
“On average, sea surface temperatures display a second cooling 12 months after a La Nina event. So it’s a double dipping but typically the second La Nina is smaller than the first.”
At the moment, we are entering into a phase known in climatology as the “predictability barrier”, where it’s challenging to forecast what these climate drivers could possibly do in coming months.
After the fog lifts in June or July, then we shall know if La Nina is coming back, and whether we will remain in the neutral state or El Nino is on the way.
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