A scorching heat wave in southern Australia will end 2021, a year marked by severe storms and above-average rainfall that leaves large areas of the east prone to flooding in the New Year.
After a mild start to summer, mercury in Melbourne is expected to climb to 38 ° C on New Years Eve after surging above 34 ° C on Thursday. The first day of 2022 will be just as hot, with the Bureau of Meteorology tilting 37 ° C for the Victorian capital. Most other capitals will push 30C, or get close to it.
Adelaide is the other capital of the hot state, with 39 ° C forecast for the last day of 2021 after 37.6 ° C on Thursday and a similar heat forecast for Friday.
The heat wave, which peaked in Perth over Christmas, is the first prolonged heat wave for much of the country this summer.
Many Australians, however, will remember 2021 – as long as they ventured away from their homes locked or constrained by Covid-19 – as a time when they had to keep an umbrella handy.
The New South Wales coast, including Sydney, was hit by days of heavy rain in March. The week ending March 24 was the region’s wettest week, according to Bureau data dating back to 1900.
Four-day totals in some areas have exceeded 900mm and the Hawkesbury-Nepean floodplain north and west of Sydney is aptly named.
Less than three months later, it was Victoria’s turn to endure savage weather, with a complex low pressure system generating heavy rains and destructive winds that left up to 200,000 people without power and toppled countless trees. Over 200mm of rain fell in the western Gippsland watershed causing extensive flooding.
Other stormy highlights included a tornado that made landfall near Bathurst in west-central New South Wales in September. Major flooding also swept long rivers such as the Lachlan and Namoi, and filled the Menindee Lakes and other inland systems.
As of the 2021 shutdown, regional dams in NSW, including the one in Sydney, are about 94% full, while Melbourne’s reservoirs are at 90% of capacity. Southeast Queensland, however, was a part of eastern Australia that missed a lot of rain, with Brisbane’s Wivenhoe Dam still less than 50% full.
In November, the Bureau said that a La Niña pattern had developed in the Pacific for the second year in a row, a weather event that tends to favor above-average precipitation for northern and eastern Australia. .
As if it did, Australia recorded its wettest November on record, breaking the previous November record set in 1973 with nationwide falls 124% above average.
“Having two sequential La Niña has particularly increased the risk of flooding this spring and summer,” said Karl Braganza, national director of climate services at the office.
“When you have a very wet month before December and the monsoon season, that’s when we start to worry about flooding from even moderate rainfall. “
The additional precipitation was influenced by other weather models, including a negative phase of the Indian Ocean Dipole. Such events typically cause increased convection off the coast of northwest Australia, causing additional moisture to flow across the continent to the southeast of the country.
Good rains over the past two years have increased soil moisture levels, which tend to moderate evaporative heat waves. One consequence is that 2021 will have been relatively cool, at least compared to the last few years.
Background warming from climate change has caused Australia’s temperatures to rise by around 1.4 ° C since 1900, reducing the likelihood of cool years – 2020, for example, was the fourth warmest year on record registered in Australia.
This year, however, is unlikely to make it into the top 10 for Heat, even with a scorching end to the year, Braganza said.
“It doesn’t tend to get that hot during the La Niña years, but you can have long stretches of hot weather,” he said.
Some of that heat will be felt this week. For areas such as western Victoria, which did not participate in the above-average falls, the current heat wave will be enough to increase the risk of bushfires.
“Southern Australia is one of the most fire-prone regions in the world every year,” adds Braganza.
During La Niñas, strengthening equatorial winds cause the Pacific Ocean to absorb more heat from the atmosphere, while El Niños causes the ocean to release some of that heat.
This year will likely be the fifth or sixth warmer on record in the world, climate scientists expect. That would make it cooler than 2020 but warmer than any year before 2014 thanks to the effect of this warming temperature background.
“It’s another really hot La Niña year,” said Braganza.
One of the threats from this warming is that coral bleaching remains a risk to the Great Barrier Reef, as Guardian Australia reported earlier this month. “There is an increased risk of heat stress on the reef until February,” he said, with a tropical cyclone being the best chance of reducing this threat.
The current La Niña is expected to persist into early next year, raising the prospect of a relatively cool and humid start to 2022 for most of eastern Australia, the bureau predicts.
For the interior of northern New South Wales and southern Queensland, these forecasts indicate an ongoing flood risk.
“The dams are pouring out, and there have been [recent] precipitation, ”Braganza said. “So they’re going to be on reasonable flood alert for the rest of the summer.”
Extensive bushfires near Perth throughout February and again in recent weeks hint at the ever-present challenge of fires in the Australian landscape. And while the eastern states are likely to experience a moderate season when it comes to wildfires, the additional rain over the past two years increases potential risks for the summers to come.
“Of course there is vegetation growth,” Braganza said. “And we know things can dry out pretty quickly. “