TWO very different weather patterns resulted in a big contrast between the weather of 2019 and 2020, but despite being a year with a La Nina forming, last year still ranks among the fourth warmest on record for Australia.
In the Bureau of Meteorology's annual climate statement, it was revealed the average mean temperature nationally was up 1.15 degrees Celsius for the year.
BoM senior climatologist Lynette Bettio said 2020 continued on from a "run of really warm years seen in recent years".
Of the other warmest years on record, number one went to 2019, with the second warmest in 2013 and the third in 2005.
It was not quite so bad in SA, where large parts of the state - including the Eyre Peninsula, Far North, Riverland, South East, Mid North and Fleurieu - experienced average mean temperatures.
But there were areas, such as the far north-east pastoral areas and parts of the West Coast, that had above average mean temperatures, while along the western border, temperatures were "very much above average".
There were several very dry months offset by a much wetter than average end to winter and start of spring.
This fits with a year that was the second warmest on record for WA.
Dr Bettio said mean maximum and mean minimum temperatures were warmer than average across the west of the state and parts of the north while being close to or cooler than average for much of the south and east.
This does include some very warm months, including SA's warmest November on record, but the state also experienced its coolest May since 2006.
Despite the warm, rainfall for most of Australia in 2020 was close to average - up 4 per cent on the national average - while 2019 was also the driest year on record, nationally.
Even with the increase in rain across large areas of the east coast, Dr Bettio said there were still a number of drier areas.
"WA didn't receive any real relief from the long-term drought of recent years," she said.
There were other areas of Qld that were also below average rainfall, although not as dry as in 2019.
In SA, rainfall was close to average across most of the state.
"There were several very dry months offset by a much wetter than average end to winter and start of spring," she said.
The May to July period was also the seventh driest on record for southern Australia.
Much of the rain in 2020, Australia-wide, fell in December, which was the wettest December on record.
Bureau head of operational climate services Andrew Watkins said the difference in the weather between 2019 and 2020 was largely driven by the almost oppositional climate drivers.
Whereas 2019 had something close to El Nino forming in the Pacific Ocean, a positive Indian Ocean Dipole in the Indian Ocean and a negative SAM in the Southern Ocean - which are linked to hotter, drier weather - in 2020, a moderate strength La Nina formed, the IOD was negative and there was a positive SAM, which is linked to easterly winds, bringing more moisture from the Tasman.
While Dr Watkins said it was unusual for a La Nina year to be so warm, he said 2020 was also a year that did not have a significant La Nina influence until quite late, with the pattern only declared in late September and spring, rather than in autumn as is often the case.
"La Nina is at its peak at the moment and we expect it to wane as we head into autumn," he said.
The good rainfall has helped boost some of the water storage along the Murray-Darling Basin, which has gone from 35.4pc at the end of 2019 to 58pc at the end of 2020.
But this has largely occurred in the southern basin, which has had water storage lift to 65.8pc, while the northern basin is still just 23.6pc.
Dr Bettio said recent rainfall in Qld, partly driven by tropical weather, should hopefully help refill some of the northern storages.
Despite that, she says the long-term impacts of the drought on the environment along the basin may take months or even years to recover.
Dr Watkins said the rainfall deficiency experienced since 2017 across large parts of the country could be considered a "flash drought", with the lack of rain also acommpanied by very high evaporation rates that also dried out the rivers and soils.
Even with the above average rain in many parts, there are still large areas, including in SA, that are experiencing serious, severe and "lowest on record" rainfall deficiencies.
"It's not until we get the rivers up and flowing well and get the soils wet that we can say we're out of the drought," he said.
The hottest day in 2020 occurred on January 4, with a temperature of 48.9C at Penrith Lakes - in Greater Sydney - while the coldest temperature of -14.2C was recorded in August in Tas.
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