Year of storms and wild weather: New Year’s Eve heatwave hits after a sodden 2021 for much of Australia

Despite a hot end to the year, many Australians will remember 2021 as a year of rain, floods and wild storms. Photograph: David Gray/AFP/Getty Images

A sizzling heatwave across southern Australia will close out 2021, a year marked by severe storms and above-average rainfall that leaves large areas of the east exposed to flooding in the new year.

After a mild start to summer, the mercury in Melbourne is forecast to climb to 38C on New Year’s Eve after topping 34C on Thursday. The first day of 2022 will be similarly hot, with the Bureau of Meteorology tipping 37C for the Victorian capital. Most other capitals will nudge 30C, or be close to it.

Adelaide is the other hot state capital, with 39C predicted for the final day of 2021 after 37.6C on Thursday and similar warmth forecast for Friday.

The heatwave, which crested in Perth over Christmas, is the first extended hot spell for much of the country this summer.

Perth metro just recorded 4 days in a row over 40 C
Sat 42.8C
Sun 43.5C
Mon 41.0C
Tues 40.7C (so far)
This is the first time in December this has occurred and 3rd time ever
Previous times were Feb 2016 and Feb 1933
📷 T. Smith, South Cottesloe https://t.co/qLf9e7uf0E pic.twitter.com/mgE4JTlTR7

— Bureau of Meteorology, Australia (@BOM_au) December 28, 2021

Many Australians, though, will remember 2021 – to the extent they ventured far from their locked-down or Covid-19 constrained homes – as one in which they needed to keep an umbrella handy.

Coastal NSW, including Sydney, was pelted by multiple days of heavy rain in March. The week ending 24 March was the region’s wettest week in Bureau data going back to 1900.

A flooded street in Port Macquarie, NSW, in march 2021. Thousands of residents fled their homes, schools were shut, and scores of people were rescued as NSW was hit by once-in-a-generation flooding. Photograph: Jason O’Brien/AAP

Four-day totals in some areas topped 900mm and the Hawkesbury-Nepean floodplain to Sydney’s north and west lived up its name.

Less than three months later, it was Victoria’s turn to endure wild weather, with a complex low pressure system generating heavy rain and damaging winds that left as many as 200,000 people without electricity and toppled countless trees. More than 200mm of rain fell in west Gippsland catchment, resulting in major flooding.

Other stormy highlights included a tornado that touched down near Bathurst in central western NSW in September. Major floods also swept down long rivers such as the Lachlan and Namoi, and filled the Menindee Lakes and other inland systems.

The tornado as it came through Bathurst, NSW, in September 2021. Photograph: Dean Whiting/dean_o_photography

As 2021 closes, regional NSW dams including Sydney’s are about 94% full, while Melbourne’s reservoirs are at 90% capacity. South-eastern Queensland, though, was one patch of eastern Australia that missed out on a lot of rain, with Brisbane’s Wivenhoe dam still under 50% full.

In November, the Bureau declared a La Niña pattern had developed in the Pacific for a second year in row, a weather event that tends to favour above-average rainfall for northern and eastern Australia.

As if on cue, Australia posted its wettest November on record, beating the previous November record set in 1973 with countrywide falls 124% above average.

“Having two sequential La Niñas has particularly elevated the flood risk this spring and summer,” said Karl Braganza, the Bureau’s national manager of climate services.

“When you have a really wet month leading into December, and into the monsoon season, that’s when we start to get worried about flooding from even moderate rainfall.”

Meanwhile in the east, flood waters remain in northern NSWhttps://t.co/8pjsT2Hz5o pic.twitter.com/RIBUZUiBU4

— Andrew B. Watkins (@windjunky) December 29, 2021

The extra rainfall was influenced by other weather patterns, including a negative phase of the Indian Ocean Dipole. Such events typically cause increased convection off north-western Australia, resulting in additional moisture making its way across the continent to the country’s south-east.

Good rains during the past two years have increased soil moisture levels, which tend to moderate heatwaves through evaporation. One consequence is that 2021 will have been relatively cool, at least compared with recent years.

The background warming from climate change has pushed Australia’s temperatures up about 1.4 C since 1900, reducing the likelihood of cool years – 2020, for instance, was Australia’s fourth-hottest on record.

This year, though, will probably fail to break into the top 10 for warmth even with the scorching end to the year, Braganza said.

Thousands of Victorians were without power for days after a deadly storm lashed eastern parts of the state in June 2021. Photograph: Daniel Pockett/AAP

“It doesn’t tend to get as hot during La Niña years but you can have extended runs of hot weather,” he said.

Some of that heat will be felt this week. For areas such as western Victoria, which have not shared in the above-average falls, the present heatwave will be enough to nudge bushfire risks higher.

“Southern Australia is one of the most fire-prone regions of the world in any year,” Braganza adds.

During La Niñas, strengthening equatorial winds result in the Pacific Ocean absorbing more heat from the atmosphere, whereas El Niños cause the ocean to give some of that warmth back.

This year will probably be about the fifth or sixth warmest on record globally, climatologists expect. That would make it cooler than 2020 but warmer than any year prior to 2014 thanks to the effect of that warming temperature background.

“It’s another really warm La Niña year,” Braganza said.

Firefighters battled a major bushfire in Western Australia’s Margaret River region early in December 2021. The fire ripped through more than 6000 hectares in the Leeuwin-Naturaliste national park within two days. Photograph: Sean Blocksidge/PR IMAGE

One threat from that heating is that coral bleaching remains a risk for the Great Barrier Reef, as Guardian Australia reported earlier this month. “There’s a heightened risk of thermal stress on the Reef out to February,” he said, with a tropical cyclone the best chance of reducing that threat.

The current La Niña is forecast to linger into early next year, raising the prospects for a relatively cool and damp start to 2022 for most of eastern Australia, the bureau predicts.

For inland northern NSW and southern Queensland, that forecast points to ongoing flood risks.

“The dams are spilling, and there was quite significant [recent] rainfall,” Braganza said. “So they’re going to be on a reasonable flood alert for the rest of summer.”

Extensive bushfires near Perth in February and again in recent weeks hint at the ever-present challenge of fires in the Australia landscape. And while eastern states are likely to have a subdued season as far as forest fires go, the added rain over the past two years elevates potential risks in coming summers.

“Of course, there’s vegetation growth,” Braganza said. “ And we know things can dry out quite quickly.”