Transcript for Summary findings from Victorian Water and Climate Initiative Phase 2

Transcript VicWaCI 2 Summary Findings

[Speaker: Anna May (DEECA)]

I'd like to begin by acknowledging traditional owners of the lands we're meeting on today, the Wurundjeri people, and pay my respects to the elders past and present. I'd like to extend that acknowledgement to the Traditional Owners and the lands where people are coming from online today and dialing in from. So I've got quite a few of online of you online and I can see more being admitted as we go as well.
Given the nature of the forum, I'd like to also reflect on the Traditional owners as Australia's first scientists who use their knowledge of climate and water to care for country. For thousands of years, for many, many generations traditional owners have continued to care for country waterways, maintaining the health and flow of water and sustaining connections to place, each other, animals, culture and community. And the role we all have in this room today, to continue that, to care for country in partnership with traditional owners is really important.

My name is Anna May, I'm the director of water access and planning in the Victorian Department of Energy, Environment, Climate and Action. That's DEECA and I have had the privilege of having the VicWaCI program in my branch for the last 8 years. I didn't realise that until someone wrote that in my speaking notes. Feeling a little bit old, but I'm very glad I've got big writing on this piece of paper because my eyes have gone over that time as well.

In my branch as well, I've got a range of other teams really focused on the technical evidence base and to share insights on how water resources are changing to inform our decision making, whether they that be what research we should be investing in next, what infrastructure decisions we should be making or policy development. But this program, the VicWaCI program, is really guided by the staff in the hydrology and Climate and Energy team within my branch, and they've done an enormous amount of work pulling together today. So thank you.

Today we brought together a range of people who have interests in this topic and we are working. We'll hear from some of them today through the presentations. We've got some science speakers presenting the research that they've developed over the course of VicWaCI, but also some of our practitioners on our panel as well to really think about how we can apply that science as well.

The timing of today's session is quite appropriate given Sunday is World Water Day. And yes, you can pop that on your list of things to celebrate this weekend as well and have a chat with your family and friends. World Water Day celebrates water and inspires action to tackle the global water crisis, which science being key to ensuring we have informed water management.

I've got a paragraph here to talk about tech issues but I'm not going to do that because I've already spent enough time on that. But if you are having any problems online, please just pop it in the chat and the team will try and help you out.

So research from second phase of VicWaCI has been summarised in the report titled Victoria's Water Resources under a Changing Climate that was released late last year. The science from the program feeds into many different applications, including the update from last year's DEECAs Water availability climate change guidelines. In the guidelines that includes new projections, We've now got a bit of a narrower range and less severe climate change impacts being projected because of the actions that we've taken across globally. Really we look out to 2080 and we've got seasonality and we also draw on the rainfall runoff response to shift that we've seen as well.
So some of the applications are the guidelines and then how that might be applied to a range of different things. But I think we've got a whole lot of practitioners as well as researchers in the audience today, both in person and online. And I really encourage you to think about the science, what it's telling you and how it could be applied to your specific context. And really encourage you to have that conversation with others, including people in the Hydrology, Climate and Energy team, to really focus where we can provide that further advice and guidance forward. But also where you think there might be some research gaps as well, because that can inform the conversation for our next phase of research.

Through the session this afternoon, we're wanting to provide you with an overview of some of the findings in the most recent phase of the VicWaCI program, in addition to discussing some of the ways the knowledge can be applied to the water sector.

So today is a wonderful opportunity for the water sector stakeholders and researchers to engage in exchange and ideas, and hopefully you started that because of the delayed start. That's a bonus, hopefully, but also encourage you to ask lots of questions to the presenters today, to others you're speaking to within the room, and really continue that conversation because that's how we get a better shared understanding and improve our understanding moving forward.

I'd like to thank those of you who have worked on the VicWaCI program and acknowledge the contributions from the broader research community through various collaborations. And I know some of you in the room have been involved in this program for many, many, many years through its infancies as well.

Together, you've provided an important evidence base for water management across Victoria, and I thinkthat's something to be really, really proud of. To our stakeholders, thank you for supporting VicWaCI over the years. We hope the findings from the second phase can continue to be useful in your work as we continue to adapt to climate change.

And before I hand over to Geoff, he manages the Hydrology and Climate Change team and he'll take you through a bit of the agenda for today, some housekeeping, et cetera. I wanted to reflect on something one of the team members said to me earlier this week. They described today as a bit of a celebration, and I think that's appropriate. It takes years to undertake research, takes years to package up that research in a usable format and to communicate it in a way that's digestible.

So I really would like to take this opportunity today as a bit of a celebration of actually being able to communicate that research. So thank you, that team member, they know who it is for describing it in that way and also acknowledge that it's that continued conversation as well.

So as I said earlier, really think about what you're hearing today from your context and think about, well, where might the gaps be? How might we want to use this research moving forward? Because science is nothing unless we continue to use it and have that conversation.

But thank you very much and I'll hand over to Geoff.

[[Speaker: Geoff Steendam (DEECA)]

Thanks, Anna.

So now the next test is whether the slides work. Did they do? Yeah, actually great success. So just before we get into some of the presentations, just a little bit of context and first up, housekeeping.

So apologies for the delayed start, but it is really great that we can do this hybrid to cater for people in the room and at home or elsewhere. For those in the room, the toilets are just out this door here to the to the right of the stage and the quickest exit is actually the door that everyone came in. So if we did need to evacuate, but also the centre staff will come in and give us instructions.

OK, So the agenda for today, so we'll have before a short break and we might sort of tighten up the times a bit. So we might pull some of these times back a little to catch up. But after this quick bit of context, we'll get into some presentations on the synthesis report of the summary report from the second phase of the Victorian water and climbing initiative, VicWaCI. So with Pandora, Francis and Sandra talking through that. And then after the break we will we will then have a couple of more specific talks focusing on a rainfall talk from Acacia and then a case study for the Maryborough supply system from David. And then we'll have a short panel session. And the purpose of the panel session is really to have a brief discussion from different perspectives, different roles in the water sector about how this kind of work can benefit and be used for application. Because of course, that's the reason why we, we invest in in all this research. OK. And we'll finish up by 4:30.

So then the purpose mainly of today is to really give this overview of the second phase of the program, which is all captured here in this synthesis or summary report placed on the website water.victoria.gov.au back in September. It is, it is really summarising the work of the program, but really in the broader body of science so that it's really giving that full picture of what practitioners need to know from the science about these kind of issues around climate, hydrology and really what it means for water resources. And we've tried to summarise a lot of that into sort of points and quotes that people could use and, and take for a whole range of different purposes. We've also got an 'at a glance' sort of summary version of that report as well, given the reports. Fairly solid at 100 pages, but lots of really great content in there.

Really thank all the contributors. There's many that are listed here. So really appreciate all the contributions. OK.

So the second phase, as I said, released the report in September That of course builds off well, primarily the work of the Bureau of Meteorology (BOM) and CSIRO, but also other content in there as well that you'll hear about. This work though builds up a whole history of 20 years or so plus, plus the full body of science out there.

But many of the programs that precede this, that many in the room have been very involved in over the years and, and we're really building on that body of knowledge with this most recent bit of work here. Of course we've got then application of that. So that's something we're constantly doing over time in in feeding it into lots of different applications across the water sector.

And there is further work, further research to come to. So I've currently got work running with the CSIRO that's continuing on a lot of this kind of work. And obviously with anything we do invest in more is looking at what's the best value for the water sector in terms of policy information planning and management decision making. What can we get that gives us the best value in regard to that?

And I think this is the last slide I was going to have, which is really just to point out on the research side of things, there's a whole lot of collaboration that goes on and that's within science community. But even within DEECA, different programs within DEECA and more broadly, just some, some examples are listed here.

Some of these things our team in DEECA investing, you know, financially or their timing to in different ways or science community more broadly connected into a lot of these activities. And so those linkages are really important. They add to the value that we get out of our program as well. And on the application side, there's similarly lots of collaboration that occurs as well. So many other application related collaborations and linkages not shown here.

So now I'll hand over to Jacqui to just introduce Pandora and then yeah, the other speakers from there.

[[Speaker: Jacqui Lloyd (DEECA)]

Got it. Thanks. Yes, I'd like to invite up some people now who are going to share some summary summaries from the VicWaCI research doctor.

Pandora Hope is the principal research scientist at the Bureau of Meteorology. Pandora's research interests is in outstanding and quantifying the influence from a range of drivers on weather and climate extremes, climate variability and change. And as per Geoff's earlier slide, Pandora was one of the leads from the BOM on the VicWaCI research program.

[[Speaker: Pandora Hope (Bureau of Meteorology)]

No worries. Very exciting to present to you today, but there's not much time. So I'm going to be rushing through things, assuming quite a lot of which I'm sure you will have see.

So the work under the Bureau of Meteorology in VicWaCI 2 fell under 4 different aspects, weather and climate interactions, how climate drivers modulate weather systems and Acacia is going to be presenting a little bit more on weather systems. I'm going to leave a lot of that to the side. And then climate drivers, seasonal differences and long-term changes in their behaviour, but also other drivers, particularly stratospheric ozone and Julian isolation, things that might be influencing the rainfall. And then looking at the step changes in our rainfall and the projection and then how any of that might influence stream flow regime, which is also something Surendra looking at. And we each had a few different approaches. And of course, the communication climate literacy. And so across the program, we've had over 40.

(Inaudible) It's sorry.

Anyway, so we had people under each of these scenes, Irina, Acacia, Blair Trewin and Jen were doing observational analysis. Surendra on the step changes Ghyslaine, Eun-Pa, Roseanna, Sharmila, note Sharmila, her name is misspelt in the report and her papers have an R in there; Chiara and then Ulrike and others involved in the stream regiments change and together we did over 40 papers and reports and of course the key one was our synthesis report.

So I'll be drawing on a few new points from the synthesis report, but extending it a little bit so you can go into the synthesis report and read a lot of this stuff. But I wanted to just talk about where we are at the cutting edge. So really want to focus the whole talk on rainfall variability on time scales of days to seasons to decades. So that is the time series of annual rainfall only in Victoria. And you know, there's a lot of things going on, particularly when there's Millennium drought rainfalls. We have presented a few webinars which you can also go back, go back to and have a look at. So understanding wet and dry ratings in Southeast Australia is just one of those.

Starting with this diagram, Figure 2.6. So this is connecting together all the things that might be influencing the rainfall variability in Victoria. You've got the weather systems highs, the lows, the fronts. You've then got the Madden-Julian oscillation which oscillates on sub seasonal and then your ENSO, Nina, El Nino from the Pacific Ocean, the Indian Ocean Dipole from the Indian Ocean. And I'm sure everyone here knows all about them, yes?

But then we also have some features further South and that wiggly line is the Eddy Driven Jet (EDJ) and the Southern Annular Mode (SAM) is the vacillation of that jet as it moves upwards towards us and then as it moves back towards the pole. And you've also got some orange lines there, the subtropical Ridge on a seasonal time scale, these commuting South as the seasons move, all of those interact together to bring us our rainfall variability in Victoria. So let's dive under the hood.

So on a very short time scale, and partly this is just because the beautiful graphics, Sharmila's work, it's going to be coming out in our JSHESS Journal, solid hemisphere journal very soon. And so if you have a heat wave in a very dry summer, you canget that followed by extreme rainfall. What sets that up?

I'm going to be flying through really quickly. So please go and engage in the report and all the papers linked to it afterwards, if you would.

So the other really key aspect is by season. So on the left we have summer DJF, then autumn, winter, spring and the correlation of rainfall with on the top row. And so, so you can see in spring, if you have an El Nino, it's going to be pretty dry across all of Victoria. That's sort of something you all know. Or if it's a La Nina, it'd be pretty wet. So that's something we all know.

The next route down is actually the East Pacific El Nino or La Nina. And so that's sort of your traditional situation. That was more predominant actually in the 80s and 90s. And then that has slightly different features. But then if we come to the Central Pacific, El Nino or La Nina, you can actually see that there's differences in autumn. And so the signatures are somewhat drier in autumn within El Nino. If it's a central Pacific ENSO.

So there's differences in where the El Nino sits in the Pacific to how it influences rainfall in our region. Indian Ocean Dipole has had a growing influence on Victoria's rainfall. You may have noticed that over the years. And it can have very big impacts in spring. And, and then at the bottom here, we have the second annular mode. So that's that north, South movement of the jet. And it can vary on different time scales. But the other key thing to notice is in winter, you can see that it brings us very dry conditions. But in the other seasons, it actually can bring us wet conditions if it's in its positive phase.

So it's positive phase, you have this little map down the bottom here in the globe. It actually is bringing wet conditions to the east. And it varies. So just allowed to move freely 10 day time scale, but it can persist for months and it can be driven to persist for months by a La Nina, it can be driven to persist for months by what's happening in the stratospheric ozone over Antarctica. And we'll go into that in the next slide. And the projections, the climate change projections are that it will trend towards the positive. So thinking about that line there, which is what we would expect positive SAM is something you might look for in your projections.

So the Antarctic Polar Vortex I think is the really important thing that's come out of the recent research in VicWaCI, something we sort of didn't really know about before. And now we can see that it's actually having impacts in how things interact and bring different framework patterns to Victoria. So it's about 30 to 50 kilometers above Antarctica swirling around. It breaks down at the end of sort of early spring and then comes down and impacts our region late spring summer. And so this Antarctic vortex strength plot on the top goes from 1980 to present and you can see the last four years, sorry, not present, 2020 to 2023 is the last four years. And they were all unusually strong. Link to in the bottom here you can see these red bars, Southern Annual Mode being predominantly in its positive phase, July four years in a row, which is pretty unusual. Before that was 2019. And there's a really nice write up of that box A in the report and check it out.

So what does this mean for season that we might have, for instance, La Nina, which we know is linked to very wet conditions, a negative phase Indian Ocean Dipole also linked to negative, sorry to very wet conditions. And you can sort of see together to the north of Australia, there's this warm air, warm waters and convection rising. So you'd expect this nice wet conditions. Alongside that we had those three years of Strong Polar Vortex which led to positive SAM and all three together are pushing Australian rainfall, Victorian rainfall to be wet. And it was, it was crazy wet in spring 2022 and I'm sure you all knew what that was linked to.

But sometimes seasons are a bit atypical. We have a La Nina or an El Nino and it's not going in the direction that we expect. And that can be because the different drivers are not interacting together, they're not working together. So three different seasons that we'll have a look at now.

So let's have a look at the wet conditions in 2023 December during an El Nino. So an El Nino, you would imagine that there would be very dry conditions before but this year, but you can see the blue, green, purple colours were very wet. And this was linked to that fourth year of that strong Polar Vortex where we had positive SAM pushing things into a wet condition. We also had Rossby wave breaking and weather. Sometimes the climate features aren't going to totally push the weather in the one direction where the systems can come in like a tropical cyclone that you didn't know.

This is another year, so spring 2025. That's just the last one that we've experienced. We had an El Nino, sorry, we had a La Nina and a strong negative IOD, but they were fighting with stratospheric warming that was actually pushing us to a negative phase of the SAM. And so in the end, what I find quite interesting, we have the wet climate conditions from the Indian Ocean Dipole down here in southern part of Victoria, but this easterly flow into that negative SAM is actually impacting eastern Victoria and NSW. And so you can kind of see the climate drivers in this pack. So what does that mean for water resources?

Another example, something you may have heard of is the Millennium Drought. And so interestingly, so I'm going to start with the bottom row here. And what I want you to look at is this blue line that's sort of coming down here, bit low, the Millennium drought in here, that's autumn, autumn rainfall, very strong decline through the Millennium drought. And we can actually think about in the middle plot here, any inertial dry fold links to ENSO. And so normally they would be strong. Normally they work together and you can see the correlation in these different colours, which are just different seasons. The correlation is actually very high in the early sort of 1960s, nineteen seventies, 1980s. But then as we come into the Millennium drought. That correlation drops away. In fact, it might even turn negative. And so you've got an Indian Ocean Dipole and a ENSO phase that are not working together. So through the Millennium drought, there were La Ninas that were not wet. So that is, you know, driven by this. And so the links to the water vapor of the maritime continent where they are all coming together will weaken as well through that. Just that top plot that if the Indian Ocean Dipole water vapor over the maritime continent?

And so what was driving that? We had a deep dive and it seems that some of the multi decadal modes in the Atlantic Ocean basin, Pacific Ocean basin were actually in a mode that was driving a disconnect between the Indian Ocean and the Pacific. And so we weren't getting that usual strong association. So we have that weakening in these blue boxes weakening that connection then low to moderate over the maritime continent which is to our north of New Guinea, Indonesia, that region. And so no very wet months were experienced through that time. Stream flow didn't recover in some of the basins and we had the Millennium drought.

I would argue though couple of minutes awesome we've got to get through the Millennium drought. I would argue that perhaps you know we talk about this decadal oscillations, it's 15 to 30 years over 30 years, we may actually be starting to seen change signature. And so I just want to put that out there as a possibility that it isn't only decadal variability, but perhaps also change.

So if we jump forward, one other aspect of what might be going on that was driving the very dry period of the Millennium drought was perhaps this on the bottom graph here is the growth of the ozone hole. So through the 1980s it started to expand this ozone hole and the impact of that has actually in new research, very exciting, been found to have an impact similar to what we see if we look at the autumn rainfall decline through that period. And so that is now stabilised due to the Montreal Protocol, well done everyone for reducing your CFCs, and is projected to reverse by mid-21st century. So that may mean the ozone related autumn rainfall component of our decline that may recover. So we have a lot of research to do that too.

And so what does that mean for our stream flow from our season and where the peak is overtime? I think you can see the blue is pre-Millennium drought, but in the yellow is Millennium drought and it was just much later in the year because we won't be seeing that water. Now some of that has recovered and we can see that the green which is post Millennium drought, we have got that earlier peak again, but it doesn't this we don't have that rainfall through into spring. And thank you for pushing forward on time. There is a webinar all about that. Please go and have a look at that.

Future climates. Could we see a drought longer or worse than the Millenium Drought and how confident are we? Now I've been told I've only got about a minute. So let's see if we can jump through these slides quickly. I want two of them. I want the one the one before this one, that one beautiful.

See, we have the Millennium drought on the left, very extreme. And this is just a PDF of the anomaly of that period of time. So that 20 years compared to any other 20 years. And on average you can see it's a, it forms a nice PDF. And in the black is a climate without climate change and in the blue is our present climate. And the red line is what the Millennium drought reduction looked like. And so it's extremely rare, but climate change did make it more likely. So it is possible that we might see something like that again and probably looking at the projections, quite likely I'll jump forward two we know temperatures going out, we know rainfall and cool seasons going down and one more forward. This is the key point.

So on this graph in the blocks, we have the comparison, the strength of the negative step changes. So they've been described this decline in the late 90s as a step change down. How often might that happen? If we look at all the climate models, if we don't have any climate change on the left there we've got the last century and we've got the coming century. So we divide at 2000 into two centuries and you can see that there's little change between the 20th century and the 21st century if you didn't have climate change, but we have. And so we look at this one on the right, which is the strongest forcing of greenhouse gases. And last century we had declines that could have included, if we're very unlucky, this observed sent step down in mid 1990s. But now if we look at what we might expect this century, it's much more likely than some of this realisations of the climate models are showing. Changes we just don't want to think about, but they're there.

So just to point out that it's becoming far more likely, but I'd say what will rainfall in the next decade be? And I think there's quite a few things we can think about. Climate change, certainly that long-term drying trend in the cool season, but climate change also warmer temperatures and the potential for intense rain, particularly on short time scales. Ozone hole, will it recover? What does that look like? A decadal variability.

Thank you.

[[Speaker: Jacqui Lloyd (DEECA)]

Thank you very much, Pandora.

I'm not sure do we have time, Geoff? Hold off questions from this whole session. Right, yeah, we, we might have time for some questions. So please keep them in your brain. We can take some questions hopefully a little later. We've also, we have a feedback form which we'll be distributing to our friends online and here in the room as well, where if you don't have an opportunity to ask you a question, you can put it to us later. A little slip of paper around.

Francis is already up. He knows he's next. Good one. So this is next one, Doctor Francis Chiew, who's a senior principal research scientist at CSIRO Environment Research Unit. Francis is a group leader of Surface Water and Basin Outcome, working with hydrologists and other researchers on water resource assessment, hydrological forecasting and prediction, climate change adaptation, and integrated basin management. Thank you, Francis, for speaking with us today.

[[Speaker: Francis Chiew (DEECA)]

Hey, thanks, Jacqui. Yeah, All right, I'll move on from Pandora's presentation and talk about the CSIRO aspects of findings from VicWaCI Phase 2, so we were really looking at a lot in the hydroclimate and hydrological modelling research. And maybe the next slide.

It's a long program and so there's quite a number of people involved in the program. So obviously what I'm presenting is really worked by a lot of these good people. And if you go on to the next slide, I'm really being talked mainly around you can think about our work as two key pieces of work. One is around evolving the hydroclimate projections and how we actually use that and apply that here.
It's also about modelling hydrological non stationarity so that we can actually robustly project or predict the future. But I think an important thing to mention is also the length of the program that has been that has been on. I think Anna mentioned some of that.

It's really the importance of having a program like this that that gets us to actually incrementally increase the understanding. I think you would argue that a lot of stuff is that we know about hydroclimate in southeastern Australia comes from programs like this. It's really that investment that has actually allowed us to move to move forward. And it's not only useful for Victoria, but the same science has been used like in the Murray Darling Basin and you hear about that and even in East Coast and so forth. So that's the importance of a long program like this.

And I think in Victoria the benefits is are eager having the foresight to actually have a team dedicated to try to convert this into. I don't think I'm involved in, I'm involved in many research studies a lot that time we do science for the sake of science also. But this is one good example where the science that we do are translated very quickly to, to, to applications, knowledge, tools and datasets that are used by the community. So that's an important thing to actually mention also. And I'll start the presentation by going on to the next slide.

I might start with the future of run on projections which are which you are adopting as, as per the guidelines. So you've got much more detailed projections in the guidelines. So it might be worthwhile just mentioning that how we came about deliveringvthese projections and how it came from VicWaCI 2 research. So it really comes from the from, from, from hydrological modelling informed by CMIP6 global climate models. And what we do is we model considering the changes in in our future seasonal rainfall in the seasonal potential evapotranspiration and a heavy, very heavy rainfall.

I think an interesting thing to note is compared to the previous round of projections that you were using guidelines rather than considering future time slice versus a historical time slice. If you. Must be me. (Sound disappears)

Can you hear us again online? Somebody could do a message or thumbs up. All right, that's good. Yeah.

So, so we can actually present that as change per degree global warming. So you could actually use it for any global warming or any SS PS at any future time in in the future. It's all about pointing out that the projections that you see, the median projections is similar to the previous iteration, but the range is smaller. And I'll talk a bit more about that.

And I think it'd be smaller again the next time we do, we do we do projections. And if you go on to the next slide, one of the things that is in people's mind is how you hear about all these things around the downscaling models, regional climate models and so forth. So it would be something not to mention, you know, the train of thought in how we develop the projections, but also mention what is out there, what is possible.

So you'll find that there's a whole series of dynamical downscale products from CORDEX. So you can't escape the fact that you hear about that. And there are actually four key modelling groups that do that. The BARPA is from the Bureau group, ACS, or CSIRO has CCAM model right in the top right, which then has a CCAM model. And there's the NARCLiM efforts are from NSW which does the WRF modelling.

So there is a synthesis of these outputs now. The Australian Climate Services has also put together a whole downscale rainfall datasets, vast vector data sets. There are really datasets that can be used. And I think a lot of this is also summarised in another division of DEECA, the climate division to the VCP 24 and the VCP 19 Victorian Climate projections.

Now, now this points to the fact that this is an important area of Australia. That's why there's so many of these products and so many research. But the same opportunity can also create confusion. And so we hear a lot from stakeholders, but which one do we use, what do we use and so forth. Suffice to say, my view is, is, is they can provide nuances, but you need a lot of expert judgement and expert interpretation of these products.

But at the broad scale, we certainly have done work in VicWaCI to which show that at a broad scale really the projections are much on muchness regardless of which method you use. And so discussion is really, you know, you embrace all of it and most of the projections that you see are embedded in there. I think in the future will rely more and more on the dynamical downscaling, especially when there's more plentiful of the run and especially if they start agreeing more with one another.

So this is not a picture which shows that the different downscaling methods, although good are not necessarily agreeing with one another on how the future looks like. So go to the next slide. I know I'm talking a lot around the averages, but you know, it's stuff that you see projections of changes in average runoff, average rainfall. They are good surrogates for things that we care about for other metrics also. But clearly they're not managing just on the averages. Really if you've got average conditions, you probably don't even have to do much management. You're actually looking at spells that you got managed for in droughts is one of them.

So I think the way the guidelines talk about and certainly we talk about it too under future climate, if you've got shifts in averages, you'll find that you're in a downward area more often, so you get more frequent and more severe hydrological drought. So if you're looking at that and that's also the guideline is you know what we think one in 20 year. How much drought that occurs once every 20 years says they become more frequent. In a medium projection it might occur once every 16 years, and in extreme projection it might actually occur twice as frequently.

So one of the resources need to manage to be able to cope, you know, with frequency and recovery from these droughts slide starts talking about variability. The projections are actually indicating that you know, our inter annual multi decal variability will increase and the climate change from stronger ENSO more El Nino, more La Nina. So a lot of conversations around is how does that further enhance the impact on the security of water resource. If you've got more of a system, you must have more problems in terms of managing the reliability of water resource systems. Now that will impact unregulated systems. If you think about the Murray Darling in the northern MDB, it will impact that significantly.

But I think in regulated systems less so because you get storage that can buffer the impact and particularly down south. Having done all this work, we're not saying that this impact is probably secondary because you've got storage pathway and because the big reductions in your rainfall runoff is already causing such a big impact. And that's sort of trying to describe it in a feature there where the bottom axis, the X axis looks at mean annual rainfall. As it shifts further left, you can see the impact becomes bigger on the reliability. But as you move upwards, it increased variability. You certainly have an enhanced impact, but small compared to relations that you see as you move, as you move towards the left.

Now this concludes probably the first part of the talk in terms of where we are going with evolving hydroclimate projection, its generation. I think you can see a lot more improvements in climate change size. We do some of it, many others do some of it, but a lot of it from hydrology. We are just really using things that we learn opportunistically with, with research that's out there. I think you'll find that we may be able to reduce the uncertainty slightly partly because of using no smart innovation in which in constraints and so on. But I doubt the next round of projections will be significantly more narrow because of you know improvements in GCM and things like that or and so forth. But I know that we will definitely try to do projections that actually separate uncertainty from climate change signal and from variability.

I think that's the difficulty in communicating the change in baseline and how to translate from variability to climate change signal. That is the same reason why our projections in this particular realm is actually narrow the range compared to the previous projections because we are removing most of the signal from the from the variability. Because I think a lot of water resource management, we actually use stochastic data to represent that. To actually have that also in the climate change signal is sort of a double counting in an interpretation. So I think in an external projections we'll do the research to be able to tease out the two uncertainty much better and just present the uncertainty from the models. So you get a narrow range of projections from climate change signal alone and then incorporate non stochastic data if you want to represent where and where you need to represent the low frequency reliability. And I think David will talk about it's done, demonstrates how some of that can be done.

Move to the second part of the talk. I hope I'm still good. Looking more in the hydrology and how climate connects to the hydrology. Most of the plots, all the plots, all the pictures that you see here comes from the synthesis report that Anna and Geoff were mentioning earlier on. So there's a lot more information in there you can refer to.

This simply shows the historical annual rainfall and run off time series as anomalies, departures from the averages. But we certainly had the Millenium Drought. But I think you'll see that we have droughts in other periods too. In fact, the federation drought was quite a long period there. I think if we had simple data there, we'll probably see similar, maybe slightly different impact as what we saw in the Millennium drought. But certainly the Millennium drought taught us a few things that I suppose wants to see. We probably cares what we should have known that anyway.

So if you look at the right hand side, which are the plotting mean annual runoff and rainfall, that's the aspects of hydrological non stationarity we're talking about: changes in your rainfall-runoff relationship. So the rainfall-runoff relationship during the drought, and the rain what this generated before and post drought is different. So you're getting less run off for the same amount of rainfall that you that you’ve had. If I were to use the same models I'm using prior to the Millennium drought, I will be heavily overestimating the runoff during the Millennium drought.

So these are the, these are the sort of non-stationarity that we are exploring to how to model that to how to model that better. And if I go on to the next slide, so there's been research over the last decade, maybe longer and looking into some of this causality of non-stationarity. That picture on the left, just a pretty picture in there and put together by Keirnan through a paper which got to have a look at 20-30 different perspectives from experts. A very good effort coming together thinking what might be driving this non stationarity, partly to understand it and partly so that we can actually model all of these.

So we think, or people think that it comes from meteorological conditions, like dry conditions, particular features, different distribution that can cause some of these non-stationarity. But I think a lot of it is due to your surface-subsurface water interaction. You just mentioned if you've got a long drought water that's sort of like a sponge, it's totally dry. You need a lot more water for the ground before you can have enough water, before you can have runoff being generated again. We also think that a lot of it has to do with vegetation dynamics and processes and that's probably can be described by what I try to do water balance picture on the right hand side, having a look at the water balance from the rainfall, ET and runoff context, actual evaporation context in the pre drought millennium drought in the post drought period.

So you've got less runoff. Sorry, you got less rainfall during the Millennium drought, but you find that the rate, vertical rate thing that actually evaporation didn't change much throughout that whole period. So and, and you and you can also see that you got a general LAI trend, vegetation trend, green trend that's moving up in Millennium Drought. So really what happened during the drought is you find that this vegetation, why they didn't die, somehow they found water from somewhere this continuing still sucking water from the ground or somewhere to, to, to continue to evaporate almost the same way.

So you put them together. If you got the rainfall reduction, the stream flow is not without using equally, it is roughly similar a lot. You will have very significant reduction in, in your runoff. And that is actually continuing in some of the catchments that you see. And there are special differences. And I think Anna or Geoff talk about that in the next slide where what is different and what has happened in south-west Victoria.

So that's also a picture from the synthesis report. And I think what that is showing on the on the map itself is how much run off there is post Millennium drought, not during Millennium drought compared to the pre drought. So many catchments in the east have sort of recovered or largely recovered from the Millennium drought, but you got a lot of catchments in the northwest Victoria and to a smaller extent southwest Victoria, which it's still in a dry period. The hydrology appears to have changed.

Yeah, and we explored some of these. We thought there's a lot of smoking guns there and so on. But largely at the end of the day, we arrived at a conclusion that you've got a hydrology non-stationarity, which I described in a previous slide. It is a drier region, so you see a bigger impact. It's a drier region with low rainfall and lower runoff coefficient, so you see a bigger impact and the rainfall post drought still relatively lower compared to rainfall recovery in eastern Victoria. Now there are also other features like lack of permanent storage, lack of permanent trees, they got more depressions and storages. We can't use that to try to explain that in in things. So yeah, in general, it's really the main thing is a trend, not broad dot points, which I put up there.

So this led to the question, especially when you're doing the development of this runoff projections to represent a non-stationarity. The question is, yeah, what hydrology do we use for thing? I think the short answer to that is from the to consider things from a climate baseline and hydrology baseline separately. So the climate baseline, you could use the full baseline or in a return water guideline, so I think you're talking about using post 75 as the as the climate baseline. But I think for the hydrology baseline, the way we model is was really you want to model it, calibrating models to post 97 conditions, you want to actually model it for today's condition and how climate can actually impact stuff that happens in this partition. But it still remains the question for management in the west of which climate baseline or hydroclimate baseline do you want to post 97 or post 75? Maybe we can discuss that later.

Page last updated: 09/07/26