TRANSCRIPT:
"Um, we now have an ocean down here."
It was a wild weekend, with train services thrown into chaos, cars left abandoned and people running for shelter as five states were smashed by thunderstorms and flash flooding.
Dr Kimberley Reid is a postdoctoral researcher at the University of Melbourne.
She says the rain storms hit New South Wales, Queensland, Victoria, Tasmania, South Australia, and the Australian Capital Territory.
"Eastern Australia was hit with what we call an atmospheric river, which is like a river of water vapour in the sky that stretched from Cairns to the south coast of Victoria. And we have a low pressure system in the great Australia helping to draw warm, moist tropical air south. On top of that, in the tropics we have what scientists call an active Madden-Julian Oscillation, but in simple terms, that's basically a pulse of storm activity that travels from the Indian Ocean to the Pacific Ocean, and that can help trigger these weather events."
Queensland has been hit hardest by the wild weather, with parts of the Gold Coast flooded by more than 200 millimetres of rain in just 24 hours.
Sydney recorded over 25 millimetres in an hour, while Canberra and Hobart each recorded around 10 millimetres in just an hour.
More than 900 calls have been made to the SES since the beginning of the week, most of which concerned fallen trees, leaking roofs and requests for sandbags.
Australian Bureau of Meteorology Angus Hines says there are particular phenomena driving these current wild weather systems.
"Broadly speaking, the link is that on warm days like we're getting, as you say, several warm days, lots of heat across southern and eastern Australia at the moment, when we get these warm temperatures, what that does is it actually promotes evaporation out of the ocean. So we get more evaporation from the oceans around Australia and that puts a lot more moisture into the atmosphere in the form of water. Vapor is at gas into the atmosphere. So when it's really hot for a prolonged period of time, you also tend to get much more humid conditions building at least near the coastlines of Australia, near those oceans around either side of the country. And then that means that we've got the fuel available when it does start to rain, to rain really heavily."
For Dr Reid, even though this scenario sounds frightening, heavy rainfall is not uncommon, especially in summer.
"What's particularly notable is that the oceans around Australia are quite warm. So for example, in the northwest of Australia, the ocean is quite warm and this is what we call a negative Indian ocean dipole. I don't think it's been officially declared, but it's close to being declared. And that's basically like La Nina in the Indian Ocean. And this warm ocean water can help sort of push tropical moist air from the tropical area down south towards Sydney and Melbourne. And so that's why we're likely to have quite a wet December."
She says it's hard to predict extreme rainfall events.
"Unlike temperature, extreme rainfall is a lot more variable. It changes from really dry to really wet. And what this means is it's much harder to pull out trends in the data, but what we know is that rainfall is caused by two key ingredients: what we call the thermodynamics, so in other words, is the air warm and is it moist? And the dynamic, so that's things like low pressure systems and cold front. And you need this combination of moisture in the air plus a weather system, like a low pressure system, to trigger a heavy flood. And so scientists are quite confident that the thermodynamic aspect, so the atmosphere being warm and moist is likely to increase, but what we're less confident about is the dynamic. So where exactly the weather systems might go."
Still, while Dr Reid says that while wet weather is not unheard of in Australia - it remains important to prepare.
"Although we're seeing quite a lot of heavy rainfall the last few years, we know that Australia can be very dry as well. And so we need to make sure we're preparing for both ends of the spectrum for very dry and very wet. That's particularly for Eastern Australia. For Western Australia, we're seeing a lot more drying happening and so they would probably want to emphasise preparing for more drought and more bush fire."
Climate change is a major factor in all of this.
So says Angus Hines.
"That's one of the main concerns actually with the climate as the way it is at the moment in this warmer climate, it means there's a lot of moisture around. So when we get heavy rainfall events, when we get extreme weather events, they're going to be even heavier in a warmer climate. The extremes are going to become even more extreme. That's the trend over the last few centuries. I think Australia is warmed by approximately one and a half degrees since the year 1900 or so. And that warming is certainly contributing to that effect of heavier rainfall too."
That's why this kind of wild weather has not been exclusive to Australia.
Notable storms have also been occurring in Spain, Chile, Brazil, Dubai and other countries this year alone - and at a time when many countries are dissatisfied with the resolutions of the United Nations Climate Change Conference in November.
But as Saint Lucia's Parliamentary Undersecretary Pauline Antoine-Prospere pointed out, the climate emergency is escalating and requires urgent solutions.
"The implications for our economies, our people and our ecosystems are severe. Our developmental gains are undermined, as national infrastructure, built with significant multilateral loans, are destroyed before the debt is paid, and we must rebuild from scratch. The cost of these catastrophes are growing exponentially, with every increment of global warming."
