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  • Rikki Lambert

Australia's climate drivers migrating south


Australia's oceans have been major weather drivers but their influence is shifting

The dominant weather systems that have traditionally influenced Australia's climate, weather and rainfall are slowly moving south, according to the head of long range forecasting at the Bureau of Meteorology.


Dr Andrew Watkins told Flow on Thursday:

"It's pretty fairly clear cut for southern Australia with that long term drying trend, unfortunately, and also the degree of warming that we've seen over the past century as well. So drier and warmer in general across southern Australia is a pretty clear pattern and we understand fairly well why that's happened.
"In terms of the actual climate drivers (it) becomes a bit more complex because with the Pacific Ocean, things have been moving a little more La Niña like, in actual fact. So a bit more warmth near Australia, a little bit cooler near South America, but in the Indian Ocean it's been going more towards a positive Indian Ocean dipole, which actually promotes drying over Australia. So we've kind of had opposite trends either side of Australia there, but the long term effect has been to push those weather systems generally further south about six kilometres a year they've been moving further south. Doesn't sound a lot, but over 50 years that's weather systems moving 300 kilometres further south. So quite clear trends over the long term. But the actual drivers themselves are a little bit of a mixed bag in how they've changed. "

Hear the full interview on the Flow podcast player below:




TRANSCRIPT:

The following is an automatically generated transcript and may contain errors. Please check against the audio above.


LAMBERT:

We're catching up with the Bureau of Meteorology's head of long range forecasts, Dr Andrew Watkins. Andrew. Welcome to Flow.


WATKINS:

Thanks. Good to be here.


LAMBERT:

Andrew, you’re no stranger to some people in our Flow broadcast areas, I understand you got involved in a recent harvest in Birchip.


WATKINS:

Oh, yeah. Well, a little while ago now. Not the most recent harvest, but the ‘21 harvest yeah. Was up there with the Ferrier family in Birchip and on the chaser Bin mostly. Had a great time and a great way to watch the weather, too.


LAMBERT:

Absolutely and farmers are always very keen to know what's likely to happen with the weather. They make major decisions off the back of that. And the last couple of seasons, of course, dominated by that. I think it's the negative Indian Ocean dipole. The La Niña phenomenon. What are they looking like they're going to do during this 2023 calendar year?


WATKINS:

Yeah. So, unfortunately, we're at that tricky time of year where it's quite difficult to make those forecasts right through the year. The good news is: well, it depends where you are, I guess, but the good news may be that La Niña is easing away at the moment. So we're seeing the temperatures out in the Pacific Ocean that basically govern La Niña and El Niño starting to ease back towards normal. (It’s) taking a little while for the atmosphere to respond. So we still might have a few wet periods yet, but it's a little early to make a prediction right through for the rest of (this year) but easing back to neutral anyway.


LAMBERT:

Yeah, that's all right. Back to neutral is good enough. But it's interesting you say the La Niña like conditions are persisting. Is that a bit of a surprise, or have we seen that sort of behaviour before?


WATKINS:

No, it's fairly typical. Or that you sort of get to a slow decline and things persist for a little while. And it's certainly not like when the Bureau declares it's on or off instantly, the rainfall changes. It's quite a complex process. It takes a while to basically dissipate. So, no, not a surprise.


What is a bit of a surprise is that the oceans are easing back a bit earlier than normal. So normally it'd be sort of February, March probably, or even a little bit later before they ease back to normal. But we've been seeing the oceans ease back to you in January and really peaked in about December.


LAMBERT:

Speaking of earlier than normal and you’re speaking of complex models you do publish, I believe you draw from a number of sources this sort of indicator of whether we're on the La Niña end of the scale or El Niño end of the scale. Where is that currently sitting? Is it sitting at the neutral position you've indicated?


WATKINS:

Look, probably just short of neutral. We still would say that we're in a La Niña type pattern, or -like pattern at the moment, but definitely easing away towards neutral. So still in La Niña, not quite neutral yet, but it's on the decline, most certainly. And then looking forward, probably over the next few months, we're likely to be in neutral conditions and getting into later into the year. We're probably looking at neutral. It's possibly the most favoured is El Niño, probably the least likely for getting out into spring and so on is La Niña at this stage.


LAMBERT:

Now, you mentioned that La Niña is bad news for some, or you've implied that. I mean, that's certainly the case, I think, for people off of Australian shores. I think it's generated drought conditions in other places. But what does it mean in southeastern Australia generally, when we do have a typical La Niña situation hanging around?


WATKINS:

Yeah. So La Niña typically brings more rainfall than normal into southeastern Australia, particularly during the winter and the spring, and often into the early parts of summer as well. Bit less of an influence later. Later in the summer tends to bring slightly cooler than normal temperatures to those areas as well. And it also brings to be a bit more humidity into southeastern Australia. So, yeah, generally. Bit more cloud, bit more humidity, bit more rain and cooler temperatures as well. And usually those combinations are usually quite okay for crop and pasture growing and so forth. But as we've seen this year, sometimes you get too much of a good thing and can turn paddocks to mud and bog headers and so forth. But also, of course, the flooding that was seen along parts of the Murray in Echuca and getting into Southeast and South Australia where the River Murray has been flooding more recently. So, yeah, got to be a little careful – can cause some difficulties, of course, but overall it's really part of our natural cycle. And good to see a bit of a recharge in terms of our dams, rivers and everything and our soil moisture after a few years drought.


LAMBERT:

Yes, it certainly is when it comes to that tropical moisture that look, I'm a layman here, it does seem that through La Niña we can see more of this tropical moisture drifting through or is that more to do with that negative Indian Ocean dipole? It's a bit of the wild card where you get the usual trough sweeping through from the south. But how does that mix with the tropical moisture? And how hard is it to predict exactly how much rain is going to fall in a particular location?


WATKINS:

Well, our weather and climate, particularly in southeastern Australia, is quite intricate Rikki a very complex interaction. You have El Niño out in the Pacific Ocean. You have the IOD, The Indian Ocean dipole out in the Indian Ocean. Then you have the Southern Ocean, which affects what's called SAM, the southern annular mode, and that directs where the fronts and so on are. And so it's a combination of all three of those large climate drivers plus some smaller things as well. In local conditions, it becomes very complex. And that's why we use these large physics and mathematics based models that are run on supercomputers to draw all that information together and make a long range forecast for all of Australia, actually all of the world, so you can look overseas and so on. So very complex. And we tend to sort of say La Niña oh, it's going to rain, but as a climatologist sort of shirks a little bit at that because it's not quite that simple. We've got all these other climate drivers mixing in as well and even just random and weather. Of course a storm on your property might not hit your neighbour’s property or vice versa. So, yeah, very complex. We use big computers, big, lots of research, climate research from around the world. All the information from satellites and ships and floating buoys and all this gets mixed into the pot and out we come with a forecast for the months ahead.

So when you have strong climate drivers, little bit easier, when those drivers aren't as clear cut, it does become a lot more complex, a lot more difficult way difficult to see him for the future months.


LAMBER:

Just lastly, some people listening, hearing us talk about climate will be wondering about what the view is regarding climate change. Are you seeing the differences in behaviours from all three of those dominant factors, those three sort of Oceanic factors when it comes to what climate change has been doing in recent years?


WATKINS:

Yeah, it is really quite complex. Again, climate change, more generally we've seen a reduction in April to October rainfall across large parts of southern Australia, including the southeast. And so, the rainfall that your grandfather may have had is generally a lot higher or higher than what we've seen in recent years right across southeastern Australia, primarily because we're getting those cold fronts and so on moving further south than they used to be.


It's pretty fairly clear cut for southern Australia with that long term drying trend, unfortunately, and also the degree of warming that we've seen over the past century as well. So drier and warmer in general across southern Australia is a pretty clear pattern and we understand fairly well why that's happened.


In terms of the actual climate drivers (it) becomes a bit more complex because with the Pacific Ocean, things have been moving a little more La Niña like, in actual fact. So a bit more warmth near Australia, a little bit cooler near South America, but in the Indian Ocean it's been going more towards a positive Indian Ocean dipole, which actually promotes drying over Australia. So we've kind of had opposite trends either side of Australia there, but the long term effect has been to push those weather systems generally further south about six kilometres a year they've been moving further south. Doesn't sound a lot, but over 50 years that's weather systems moving 300 kilometres further south. So quite clear trends over the long term. But the actual drivers themselves are a little bit of a mixed bag in how they've changed.


LAMBERT:

Plenty for our farmers and anyone else who's got a strong interest like myself in weather to unpack there lots for the scientists of the Bureau of Meteorology to work through, including at the Long range forecasting department, the head there is Dr Andrew Watkins. Thanks so much for joining us today on Flow.


WATKINS:

It's been a pleasure, Rikki.

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