2021 Australia’s Coolest Year Since 2012 and Wettest Since 2016

In this aerial view the Wyangala Dam is pictured as it spills after reaching 104% capacity in Wyangala, Australia on November 15, 2021. Photo by Brook Mitchell/Getty Images

The year 2021 was Australia’s coolest year in almost a decade and also the nation’s wettest in five years, according to the Bureau of Meteorology’s Annual Climate Statement, released on Thursday.

While the mean temperature was 0.56 degrees celsius (33 degrees Fahrenheit) above the 1961 to 1990 reference period, 2021 was around 0.4 degrees celsius cooler (32.4 degrees Fahrenheit) than the average temperature between 2011 and 2020.

Bureau of Meteorology Senior Climatologist Dr Simon Grainger said that “one of the big differences between 2021 and recent years is that it was actually much cooler in 2021 than the last decade.”

The cooler conditions were brought about by two La Niña events, the first during the summer of 2020-21 and the second commencing in November of 2021.

According to the Bureau, La Niña is a weather pattern in the tropical Pacific Ocean that brings cooler than usual maximum daytime temperatures south of the tropics and warmer overnight temperatures in the north.

The cooler temperatures in the south are the result of increased cloud cover, although this cloud cover tends to act as an insulator and can result in warmer than average minimum temperatures.

Another feature of La Nina is that it leads to increased rainfall, making it one of the contributing factors to 2021 being Australia’s wettest year since 2016. Additionally, it was the wettest November on record.

Two other climate drivers which contributed to the increased rainfall—which was 9 percent above the yearly average—were a negative Indian Ocean Dipole and a positive phase of the Southern Annular Mode.

The Bureau states that the former results in cooler sea temperatures in the western Indian Ocean; more westerly winds, bringing greater cloud cover over Australia’s northwest; and increased rainfall in the Top End and southern Australia.

The latter, when occurring in spring and summer, can result in southern Australia being influenced by the northern half of high pressure systems, leading to more easterly winds bringing moist air from the Tasman Sea, which is on the eastern side of Australia. This increased moisture can mean rain when the winds lash the east coast and the Great Dividing Range.

Grainger said that 2021 started with a La Niña, which had been declared in 2020, so this weather pattern influenced the summer of 2020-21.

Then, winter and spring saw a persistent negative Indian Ocean Dipole, which meant increased rainfall over that period, while in late spring, the La Niña re-emerged in the tropical Pacific.

In addition, late spring saw a positive phase of the Southern Annular Mode, increasing rainfall into summer.

“So the combination of La Nina events, the residual effects of the Indian Ocean Dipole, and the positive phase of the Southern Annular Mode, all of these contributed to Australia having its wettest November on record,” Grainger said.

But Grainger noted that the rainfall was welcome after three years of low rainfall across the country.

“After three years of drought from 2017 to 2019, above-average rainfall last year resulted in a welcome recharge of our water storages but also some significant flooding to eastern Australia,” he said.