Extract from ABC News
After months of speculation it is finally Bureau of Meteorology official: we are in the third La Niña in row.
Key points:
- The BOM has officially declared the La Niña is underway
- The climate driver typically brings wetter than average conditions to Australia's north and east
- This makes the third La Niña summer in a row and ups the risk of rain and flooding in the coming months
So why does this climate driver bring so much rain and what should we expect this summer?
During a La Niña, the atmospheric circulation across the tropical Pacific is set up so that warm waters to Australia's north-east and strong trade winds pump moisture into the atmosphere along Australia's east coast.
When the right systems come along they can then tap into that moisture, bringing about heavy rains and flooding.
It is something those in eastern Australia have been all too familiar with over the last two soaking La Niña summers.
"The problem with a triple La Niña is that the ground is very wet already, our rivers are quite high, our creeks are full and our dams are quite full," according to Dr Margaret Cook, environmental historian and lecturer at the University of the Sunshine Coast and researcher at Griffith University.
"So we have less capacity to absorb this enormous amount of rain."
It does not necessarily follow that this summer will definitely bring biblical floods.
But it doesn't rule out floods this summer.
What should we expect this summer?
Having two La Niñas in a row is pretty common, but three is far more unusual.
Depending on the criteria you use, there have only been two or three previous triple La Niñas since the modern records began in 1900.
It doesn't give us a huge amount of historical precedent to call upon.
But according to Zoe Gillett, climate scientist at the University of New South Wales and ARC Centre of Excellence for Climate Extremes, this round is already bucking the trends.
"When we have an El Niño it tends to trigger La Niña events," she said.
All of the previous triple La Niña events had an El Niño the year before.
"But this particular event is a bit different because it wasn't preceded by an El Niño in the previous summer," she said.
"It's a bit intriguing, something we will be trying to understand in the coming years."
How weak or strong the years within the triple La Niñas have been is also variable.
"I had a bit of a look at the numbers and in 1954 to 1957, and in the 1998 to 2001 events, the third La Niña was the weakest of the three events," Dr Gillett said.
"But for the 1973 to 1976 event, the second La Niña was the weakest.
"These past events [therefore] don't provide us with much guidance about what we can expect for this possible third consecutive La Nina."
The fall out from the past triple-dips is also inconsistent.
According to Dr Cook, the 1950s event brought enormous flooding in Queensland and northern New South Wales.
Then the infamous 1973 to 1976 triple-dip was phenomenally wet.
"1974 was the wettest year we have had on record so far throughout Australia and 1973 and 1975 were in the top five," she said.
But Dr Cook said the 1990s triple La Niña wasn't as wet.
"There was a lot of rain but we didn't have extraordinary floods," she said.
"Even when you get a triple La Niña, they are unpredictable."
How is the season shaping up?
"In our part of the world, in south-east Queensland, it still feels damp. We've still got mould, we've still got drying mud around the place," Dr Cook said.
"It has sort of got that feel of: maybe something might happen."
How long this La Niña is likely to hang around is another good question at the moment.
"We know that La Niñas and also El Niños tend to die off in autumn," Dr Gillett said.
"The current forecasts suggest that La Niña will persist until at least the end of the year."
Usually the worst floods come late summer after the ground has gone thorough a few rounds of rain.
But with catchments already sodden, it wont take much for the creeks and rivers to rise again this summer and La Niña is not the only driver out there pushing us towards rain.
We are currently in the positive phase of the Southern Annular Mode and negative phases of the Indian Ocean Dipole.
"All these phases, negative Indian Ocean Dipole, positive Southern Annular Mode and La Niña, all tend to promote increased rainfall across parts of Australia in various seasons," Dr Gillett said.
"That's what we're seeing in this upcoming period."
Just how big those floods will or could be is another story.
"We can always get floods that are worse than the last one but we can't predict that either," Dr Cook said.
What can we do to prepare?
"My main concern is that actually we are all really tired," Dr Cook said.
"We've got flood fatigue. We are all a bit over these floods and rain."
With the lingering mould and mud, many will not want to face the coming summer, but Dr Cook is optimistic the La Niña will spur people into action.
"We've got lots of warning so let's think about what's important to us and maybe start making some plans," she said.
"Have our valuables ready to go, our pets at the ready and know where we can go when the rains do set in."
ABC Emergency has a wealth of information on what you should do to get ready if the worst happens.
Prepare your home:
- Obtain a copy of your local council's flood plan, which should show the location of problem areas, evacuation routes and relief centres.
- Work out what the safest route to leave your property would be, and if you could be cut off by floodwaters.
- Sandbags can help to protect your home when used correctly. The SES or your local council is the best place to start.
- Know the kind of flooding your area is prone to. You might get advance warning if a river is rising, however flash flooding after heavy rainfall can happen within hours or minutes when runoff or drainage can’t disperse the water.
- If a flood is likely, tune in to your local ABC Radio station and keep listening for advice and warnings. You can find your local station on the ABC Radio frequency finder as well as listen online or via the ABC listen app.
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