Glen Paul: G’day, and welcome to CSIROpod, I’m Glen Paul. In recent times south-eastern Australia has experienced a range of climate extremes leading to both drought and floods. These conditions reflect both the inherent natural variability of the climate system, as well as an underlying drying trend which appears to be partly attributable to climate change.
To improve our understanding of climate variability and change in south-eastern Australia, in 2006 CSIRO partnered with the Department of Climate Change and Energy Efficiency, the Murray Darling Basin Authority, Bureau of Meteorology, and the Victorian Department of Sustainability and Environment, for the South Eastern Australian Climate Initiative, or SEACI.
Phase one of the project was completed in 2009, and now phase two has also been finalised. Joining me on the line is the Program Director of the South Eastern Australian Climate Initiative, CSIRO’s Doctor David Post. David, let’s go back to phase one of the study which wound up on the back of the millennium drought in 2009, now how did that influence the second phase of the project, particularly as it then rained, making 2010/11 the wettest two year period on record?
Dr. Post: Yes, it was an interesting time. At the end of the first phase, of course, we were still in the middle of the millennium drought, and we weren’t really sure what direction things were going to go – I mean all indications were that this drying trend was going to continue, but we didn’t really understand exactly what was causing it, and that led to most of the research in phase two, which was understanding what caused the drying trend. And of course as happens in science, as we started phase two it suddenly the heavens opened and it started raining and actually led to the wettest two year period on record. So suddenly we needed to change our research direction, understand what was going on with the climate, but also what causes these short term massive variability that we see in the climate.
Glen Paul: So how then did you investigate it and establish that it wasn’t just the result of El Niño La Niña driving this variability in south-eastern Australia?
Dr. Post: Yeah, well one of the interesting things was when the millennium drought ended in 2009, we had Australia’s actual wettest two year period on record, so we had the driest 13 year period on record during the millennium drought ever recorded in south-eastern Australia, and then that was broken by Australia’s wettest two year period on record in 2010, 2011, so it was quite extraordinary. We’ve had, you know, in the last 15 or 16 years we’ve actually had extremes that were record breaking across south-eastern Australia, quite amazing conditions.
So what happened during the floods was that actually it was the influences you mentioned, so it was things like the strongest La Niña ever recorded contributed to it, so did a factor we call the Indian Ocean Dipole that measures the state of the Indian Ocean, that was also at its most extreme in terms of bringing wet conditions to south-eastern Australia. In conjunction with that we had the warmest sea surface temperatures on record across the northern part of Australia, and we had very strong easterlies being influenced by a thing called the SAM, the Southern Oscillation Mode, and these things all came together in just incredibly perfect timing to produce unbelievable downpours of rainfall which we saw across the region, and so we understand what led to that record breaking two year wet spell.
The interesting thing about it though is that it all happened pretty much in the warm season, sort of the warm months of the year – during the cooler months of the year we actually had a rainfall decline that was as large as what we saw during the millennium drought, and it just hasn’t recovered. That’s the thing that we’re linking to climate change.
Glen Paul: OK. So you’ve found the fingerprints of climate change on some of these events, so what does that then tell us about future climate variability for south-eastern Australia?
Dr. Post: Hmm, well interestingly as this cool season rainfall decline has continued, and has continued even through the wettest two year period we’ve ever seen, we expect that that’s going to continue into the future as well. We may see wet months occasionally during the cool season, but it’s traditionally been the filling season for the dams across the Murray Darling Basin, and particularly Victoria – very reliable rainfall typically in winter in that region – that reliable rainfall hasn’t been seen to the same extent since the beginning of the millennium drought, and perhaps even earlier than that, as some of our analyses indicated.
That is predicted to continue. The global climate models can’t reproduce these observed changes in large scale atmospheric circulation without introducing factors such as increased carbon dioxide and other greenhouse gases. Now the changes I’m talking about are things such as a widening of the tropics. So what’s actually happening is the circulation called the Hadley Circulation, and everybody knows from basic high school meteorology that over the tropics you get a lot of heat, and that heat leads to the air rising, and that air moves towards the poles and then sinks again – traditionally it sort of happens over south-eastern Australia, which is sort of the mid latitudes, that’s why it tends not to be as wet here as it is over the tropical regions.
Now what’s happened is that that cell’s actually expanding, it’s growing towards the poles at the rate of about half a degree a decade, that’s about 50 kilometres a decade, and what we’re seeing is that as it moves further south across south-eastern Australia it’s pushing the storm tracks further south. Most of that cool season rainfall we use to see was from cold fronts sweeping across the continent that everybody is familiar with from the weather maps. What’s happening is those are being pushed further south and they’re tending to miss the southern part of Australia, and that is happening in south-eastern Australia, and it’s already happened, I think most people know, in south-western Western Australia, where Perth of course has had declined rainfall since about 1975. We’re starting to see those effects now in the south east of the country also.
Glen Paul: Well then will this require us to rethink how we use the water supply systems across the region, particularly if the traditional filling season is the cool season, which is going to see less rainfall?
Dr. Post: Yeah. I think one of our messages to water managers and policy makers, is they need to be very adaptive in their management strategies. Traditionally now they tend to do things under the expectation that the dams will refill during the cool season, and we saw during the 2010/11 floods most of the rainfall occurring in the warm season of the year, and then mostly through tropical influences. So it’s not all bad – you get an expansion in the tropics, meaning that some of your cool season rainfall declines, that may be compensated for, in part, by an increase in warm season rainfall, but that relies on all these other drivers, like the El Niño Southern Oscillation, the Indian Ocean Dipole, the Southern Annual Mode, all of these things that we don’t fully understand just yet how they’re going to change into the future, particularly El Niño Southern Oscillation – there’s no real clear indication which way that’s going to go under a warmer world.
Glen Paul: Hmm, so a bit of a mixed bag. But what are the key messages then that we should take away from the report?
Dr. Post: I think that primarily that this change, this decrease in cool season rainfall across south-eastern Australia, and of course south-west Western Australia, is not going to go away. Basically we’re stuck with it. You’ll still get wet months from time to time, but you’re not going to have the same sort of reliability of rainfall as what we’ve seen traditionally in the past. We may see changes in rainfall leading to increases in the warm season, but that lack of cool season rainfall means that I think that water managers need to be very adaptive in the way in which they plan their water use, because they just can’t rely on that refilling of the dams to occur every winter, like it has traditionally.
Glen Paul: So this sounds like there’s still a need for further research to see us into the future. Will there be a phase three?
Dr. Post: So there won’t be a phase three of SEACI in total across the whole region, but we’re currently planning a new climate initiative with the Victorian State Government called VICCI, the Victorian Climate Initiative, and so that will continue to look at some of these important drivers, try to understand how they might change in a warmer world, and probably just as importantly understand how those changes in rainfall are likely to lead to changes in runoff and hydrology so the water managers can more efficiently plan for changes in rainfall in the future, and ensuring continuity supply to irrigators and so forth.
Glen Paul: Well just on that, the Synthesis of findings from phase two of the South Eastern Australian Climate Initiative, as it’s called, is available now, and it’s quite comprehensive. Who should these people contact if they need further information or assistance in interpreting some of it?
Dr. Post: Even though the second phase of SEACI is now over, I’ll still be responsible for working in this region. Something that CSIRO Land and Water has an interest in is trying to help water managers to further manage their supplies into the future, so even though that’s over, we’re still here and available to assist. If people want more information they can contact me directly, and I think my email details will be on the website, and there’s an email address email@example.com they can also send requests to that and we’ll certainly endeavour to help them in whatever they need assistance with.
There are copies of the Synthesis Report available for example, and Fact Sheets which provide a fairly easy to understand, but still fairly comprehensive, summary of the findings of SEACI.
Glen Paul: Great. Alright, well thank you very much for your time today, David. Much appreciated.
Dr. Post: Quite alright. Thank you very much.
Glen Paul: Doctor David Post. And to find out more about the initiative and other research being undertaken at CSIRO, or to follow us on other social media, just go to www.csiro.au.