Australia has desperately needed rain, but not like this.
People all over the world had been hoping Australia would soon get enough rainfall to break its long, trying drought. Unprecedented bushfires have been ravaging the country for months, burning approximately , destroying over 2500 homes, and killing over 30 people. Experts estimate over have died, with recovery expected to take decades.
The recent arrival of rain was therefore a welcome relief. While it wasn’t the extinguishing blanket Australians were hoping for, and in fact , the downpour has helped to put out or contain some fires.
However, severe storms also created new, different problems, from flash flooding in Queensland to that destructive hail in Canberra. These conditions are a stark contrast to the bushfires and dry dust storms blowing across these same states, leaving many Australians to wonder what on earth is going on.
Yet according to Australian Bureau of Meteorology’s Diana Eadie, the rain at least is fairly ordinary.
“[It] is not unusual to experience such storm outbreaks at this time of year in Australia,” Eadie told Mashable. “That being said, with the sudden breakdown of drying climate drivers, the return to more typical weather has felt, to many people, rather abrupt.”
Basically, Australians haven’t seen rain in so long that the sudden return to normalcy has been overwhelming.
Why has Australia’s weather been so dry?
“Australia is currently in its severe weather season, which is characterised by severe thunderstorms, fires, floods, and tropical cyclone activity,” said Eadie.
According to her, Australia’s recent weather is affected by both global warming and patterns in the surrounding ocean and atmosphere. “These climate drivers acted to not only enhance fire dangers, but also suppress the thunderstorm activity that we would normally expect to impact eastern parts of Australia during spring and summer.”
One of these patterns is the changing temperatures in the Indian Ocean, referred to as the . The IOD goes through three phases — positive, negative, and neutral — with Australia having just having gone through a “very strong and long-lived” positive phase.
In a positive IOD, weak westerly winds allow warm water to move to the Indian Ocean’s west, away from Australia. Meanwhile, cool water rises from the depths in the east, on Australia’s north-western coast. This means there is less moisture and fewer clouds in the atmosphere around Australia, influencing the trajectory of weather systems approaching from the west.
The end result is hotter, drier conditions in central and south-east Australia, conducive to bushfires.
While the positive IOD was a primary factor affecting Australia’s weather, Eadie also noted that it compounded with the impact of the . This refers to the north or south shift of strong westerly winds which encircle the globe to the south of Australia.
A negative SAM from late October to late December shifted the winds too far north. This caused them to blow across the continent’s hot, dusty center, losing moisture by the time they reached the east coast and resulting in less rainfall.
The IOD and SAM are both normal parts of Australia’s weather cycle. What’s less normal is that conditions are also being impacted by climate change. Australia’s droughts are becoming longer, bigger, and more frequent as global temperatures trend upward, exacerbating the already hot weather to make fire seasons increasingly more extreme.
Why has Australia’s weather become so wet?
Fortunately, both the IOD and SAM have returned to more neutral phases over recent weeks. This has allowed easterly winds to carry moisture from the Coral and Tasman Seas to Australia’s east coast and tropics.
“Recently, a complex low-pressure system moved over southeast Australia, and tapped into this moisture source to result in the severe storm activity that we saw in Melbourne and Canberra in days gone by,” said Eadie.
A low pressure system is an area where the atmospheric pressure is lower than the area around it. This causes wind to move toward the system, rising and forming rain clouds. Such systems become complex when they have more than one low pressure center.
Of course, while the rain may be normal, the size of the hail is less so. Speaking to ABC News, Dr Joshua Soderholm attributed the outsized balls of ice to the formation of supercell thunderstorms — the least common and most severe type of thunderstorms.
“Supercells are special because they have very wide, strong and persistent updrafts, so you can imagine the hail growth conditions are ideal for hailstorms,” said Soderholm.
The rotating updrafts found in supercells “allows them to become more intense and persist for longer, which allows them in turn to generate larger hail.”
Do the bushfires have anything to do with the storms?
Eadie acknowledged that bushfires can create their own weather systems, forming clouds when hot air and fine particles rise to the point of condensation. They can even generate thunderstorms in extreme cases, exacerbating fire danger with lightning and gusty winds.
“However, the severe storms that have been experienced over eastern Australia recently are not directly related to the bushfires,” Eadie noted. It seems Australia is just that lucky.
Severe thunderstorms are likely to drop off after March, but until then Australians are being advised to brace for more wild weather. Though New South Wales experienced temperatures exceeding 40 degrees Celsius (104 degrees Fahrenheit) on Thursday, severe storms are forecast to hit the state’s northeast on Friday and over the weekend, potentially bringing “large hail, damaging winds, and locally heavy falls.”
While Australia’s wild weather may seem apocalyptic, it’s largely the dramatic contrasts that make it feel that way — though the size of the hail is admittedly unusual, the deluge of rain isn’t a harbinger of doom. The bushfires and drought, however, may be another story.