Transcript for A system’s approach to understanding climate change impacts on water webinar

Grace Mitchell:

Welcome to this event for the Victorian Water and Climate Initiative. For those who don't know me, I'm Grace Mitchell. My role is Executive Director of Water Resource Strategy Division here at DELWP's Water and Catchments Group. One of the many things that I oversee, and it's a great pleasure to be able to do so, is the hydrology and climate science team who manage the Victorian Water and Climate Initiative. Firstly though, I'd like to acknowledge the traditional owners on the lands on which we are meeting today. In my case, this is the lands of the Wurundjeri people of the Kulin nations, and I'd like to pay my respects to their elders past, present, and emerging. And also extend that acknowledgement to those across other parts of Victoria, Australia where people may be joining us today.

This event follows the release of the report called Victoria's Water in a Changing Climate, which was released in December. Some of you may have had a chance to read the report by now, but if not, that's okay, because the purpose of today's session is to give you a brief overview of some of the main findings from the Victorian Water and Climate Initiative or VicWaCI for short, as we like to refer to it. The research findings being presented today have been four years in the making, and they build off a longer history of the Victorian Water Climate sectors investment in this type of research, and I'm pleased to say that we continue that investment in the near coming years, so it's great to be able to have this ongoing investment in research. This programme is led by DELWP. The research of VicWaCI is being done by our research partners at the Bureau of Meteorology, the University of Melbourne and CSIRO.

I want to thank Pandora Hope, Murray Peel, and Francis Chiew from those organisations for being here today, and you'll be hearing from them soon. I would also like to thank all the others that have contributed to the research, of which there are a great number. The research process can be long and arduous, but I think the final product speaks for itself, and I know that the report, Victoria's Water in a Changing Climate, will be a great asset to the water sector for years to come.

There are many different research questions covered by VicWaCI, but the overall focus of the programme is about better understanding our climate and water resource situation, and how this is changing over time. It's important to remember that VicWaCI is about more than just research. It's ultimately about putting what we learn into practise, so we can make more informed water resource decisions, and this includes decisions about how we manage our water resources today, and how we better plan for it in the future, including responding to the challenges of climate change.

Each of today's guests will speak for about 10 minutes, after which we will have them all join us for a panel session to respond to any questions you may have. They will be joined by Geoff Steendam from the Hydrology Appliance Science team in DELWP, and this is the team that has led the VicWaCI programme, and will continue to work with stakeholders in the coming years to apply this great science.

The first presentation will be from Pandora Hope of the Australian Bureau of Meteorology's Research Division. She's particularly interested in understanding climate variability, change in extremes, and her talk will focus on Victoria's changing climate, in particular rainfall given its importance for water availability, which is covered in Chapter 2 of the report.

Pandora will be followed by Murray Peel, a senior lecturer in the Department of Infrastructure Engineering at the University of Melbourne. His research interests include catchment hydrology, and his talk today will focus on the changes we are seeing in the response of runoff to rainfall in some parts of Victoria covered in Chapter 3 of the report.

The final talk today will be by Francis Chiew. Francis is a research group leader at CSIRO working in water resource assessment, forecasting protection. Francis's talk today will focus on hydro climate projections, which is covered in Chapter 4 of the report. Like all the other VicWaCI webinars that were held last year, we will be recording this presentation and we'll make it available after the event. On a final note, I'd like to thank everybody for joining us today and hope you enjoy the event, so now it's time for us to be able to hear from Pandora, Murray and Francis. Enjoy.

Pandora Hope:

Victoria's climate is changing. How it's changing and why is important if you're managing or planning a water resource. A team of researchers from the Bureau of Meteorology in collaboration with others from the Victorian Water and Climate Initiative have had a really close look at Victoria's climate and the causes for those changes.

Turning first to temperature, looking at the average across the state every year since 1910, you can see a consistent increase in temperature since about 1950, in line with what we've seen globally with climate change. If you then turn to the rainfall variability, there's a more complex story.

The story in the cool season is different from what's happening in the warm season, so we've presented them separately. On the left is the cool season from April to October, and on the right, the warm season from November to March. Turning to the cool season, you can see the red bars starting in 1998 right through the Millennium Drought through to the present time, interspersed only with a couple of very wet years linked to La Nina, and Indian Ocean Dipole events.

The summer season has seen some significant falls through that 2010, '11, La Nina event and we might see some nice falls in this year with the La Nina that's happening now. Going back to the cool season, you can see there have been other droughts. The World War II drought is an example, but nothing quite as extensive as what we've seen in the Millennium Drought.

Through that time, we might also be interested in the months where you have very heavy rain, so the top 10% of rainfall, and we find that although these should happen once or perhaps twice each year, during the Millennium Drought, there was only one such month leading to very dry conditions right through the period. That was broken in 2010 with the La Nina, and we've since seen average to below average conditions.

Thinking about the reasons why our weather might be changing, we had a look at the weather systems. We can objectively identify highs, lows, fronts, and under VicWaCI we developed a new method to identify environments where thunderstorms might form. These are really important because in combination with some of the large-scale weather systems like a front coming right across the state, they tend to be associated with very heavy rainfall.

If we look at the rainfall from each of these types of systems, in the cool season on the top row and the warm season on the bottom row. In the top left is the rain brought by fronts and lows during the cool season, and you can see that they bring the majority of the rain, in that deeper green colour. The yellow is only about 10%, and that's the thunderstorm environments do contribute in the winter and cool season, but not very much. However, when combined with other systems, we can see very extreme rain in the right hand top panel there. In the bottom left is the amount of rain we might see from fronts or lows in the warm season, and they are important across the south of the state, but less so across the north, and there, the thunderstorms become really important. Those showery convective storms you might get in the afternoon, and combined they bring very heavy rainfall.

If you look at how these rainfall signatures have changed over time... The record from 1979, we split it at 1997, and we can see in the recent period, in the cool season the lows and fronts have brought much less rainfall. This is linked to actually fewer lows, but the amount of fronts has remained the same, but the rainfall from them has decreased. The thunderstorm story is less important in winter, as I said before, but in summer in the bottom panel there, you can see it's actually brought an increase in rainfall associated with these thunderstorm environments. The faded parts of the panels are where the rainfall's less than 25 millimetres.

In the warm season. We also see a decrease in rainfall link to those lows termed East Coast lows. Together though, in the northwest of the state, we've actually seen an increase in rainfall associated with these weather systems when they're combined. That's evident when we look at the average pattern across the state. Right across the state in the cool season, the last 23 years have been the driest of all 23 years, in many parts of the state. But in summer there's actually been a slight increase in rainfall through this period in the northwest of the state associated with those more thunderstorm-type environments.

Looking globally, we can consider the Southern Hemisphere from the equator in the right-hand part of the panel to the South Pole on the left. If we average the circulations and weather right around the hemisphere, we generally have uplift in the tropics, but descent in our region, and you can see that term, the subtropical ridge below the panel there. That's associated with high pressure systems and that's been intensifying over the last few decades, so no wonder we've been seeing more high pressure systems through that period.

Through research under VicWaCI, we've also discovered that the day-to-day unsettled conditions that we might need to have a storm form, a front coming through and strong rainfall from it for instance, we need uplift from the south to occur, and that has actually been weakening in our time series analysis of this new way of looking at the global circulation.

Considering how that time series has been changing, we can also link some of these changes to the driving factors. So increasing levels of atmospheric greenhouse gases is one, but also changes in the Antarctic ozone hole, volcanoes, and the aerosols from industrialization.

We now look at short duration, high-intensity rainfall events, just to think about how they're changing over time also. There's some indication that with increasing temperatures, these will increase in intensity, and we wanted to explore that at eight high-quality stations across Victoria. We can see in the record from 1958 to 2014, if we split it in the mid-1980s, the more recent period is in dark shading and the earlier period in light shading. But in the northwest, in Mildura, and the west, Lauriston reservoir, we do see a strong increase in the intensity of these one in a hundred-year events. This is also true in the east, though not to the same extent, and at Melbourne. Although in the central parts of the state at Eildon and at Mount St. Leonard, this is not the case, and it might be due to different weather systems and really highlights that there are regional differences across the state.

So we've used observations to understand the weather systems and the global scale circulation that's influencing Victoria's weather and climate over the last few decades. We can also draw information from global climate models, and they can inform us about how much of the signal is due to different forcing, like greenhouse gases. And we see that the decline through the Millennium Drought was caused in part by increasing levels of greenhouse gases, offset to some extent by variability introduced from volcanoes and the solar variability we see on an 11-year cycle.

Looking forward though, we can average across 40 different climate models to get the signal of what we might expect into the future, in the orange dash line there. And you can see in general it sits below the average. So that means that even though we'll get natural year-to-year variability, this year might be quiet wet, it's generally going to be a drier future. Thank you.

Murray Peel:

Good afternoon. My name's Murray Peel from the University of Melbourne, and today I'm going to be talking about the Victorian Water and Climate Initiative synthesis report Chapter 3, titled Victoria's Changing Hydrology. My collaborators on this work were Margarita Saft and Tim Peterson, and Margarita and I am at the Melbourne University. Tim was at Melbourne but is now at Monash, and this is all reporting on DELWP-funded research. So what we're going to be looking at in Chapter 3 is how Victoria's rainfall converts into runoff. And we've got some several, about 150 catchments across the state, and we can see that each year we have some dry years, some wet years, and during the Millennium Drought, which is this 13-year dry period here from 1997 to 2009, we can see that rainfall was reduced and runoff was significantly reduced across our catchments.

So what we're going to be investigating is, was the runoff reduced more than we expected, and what has happened to that runoff response after the Millennium Drought once the rainfall had a couple of wet years, and then has been not as dry as what we experienced during the drought, how has the runoff responded?

If we look at some summary stats across our 156 unregulated catchments in Victoria and the Millennium Drought was '97 to 2009, we basically had a 15% reduction in rainfall from the pre-droughts into the drought. So the drought was 15% drier. The runoff was actually significantly reduced, not quite half, but significantly reduced, and our runoff ratio dropped from 25% of rainfall becoming runoff, down to 15% of our rainfall becoming runoff. Now, we would expect some decline in runoff ratio and runoff because it's drought, but that's a fairly substantial reduction.

When we look at post-drought, the rainfall has returned back to normal, although a lot of that's due to just have couple of very wet years straight after the drought. The average runoff has not returned to normal. We're still producing less runoff than we were pre-drought, and the runoff ratio hasn't returned to normal either. So we are going to have a look at what happened to the runoff during the drought and why has it not necessarily recovered after the drought.

If we have a look at the stream flow anomaly during the drought and post-drought, and a stream flow anomaly defined here as the mean during the drought period or the post-drought period relative to the pre-drought mean. So we can see zero here is this colour here. Across Victoria we can see in the eastern catchments, we've got reductions in the order of say 20, 30%, which seems reasonable, but out in the centre and the west, we've got some very substantial reductions out here in the order of 80, possibly even 90% in some cases, which is extremely large reductions given the rainfall decline that we had.

Post-drought, we can see that the eastern catchments are pretty much back to normal, say zero change. But in centre and the west, we've still got catchments producing about 20 to 30, maybe 40% less runoff than we would expect, even though the rainfall has returned to normal. So there's clearly differences between the east and the west of the state, and not all of the runoff that we would expect is actually occurring. Let's have a look at a couple of example catchments where we can look at how the rainfall-runoff response behaves. So in these two catchments, the Wonnangatta River in Gippsland and the Loddon in north central Victoria, both catchments received a 10% reduction in rainfall from 1997 to 2016. In the Wonnangatta in Gippsland that 10% reduction rainfall converted into a 25% reduction in runoff, perfectly within what we would expect, basically for every 1% reduction rainfall, you'd expect a two to 3% reduction in runoff.

Whereas in the Loddon River, that 10% reduction in rainfall turned into a 55% reduction in runoff, which is substantially larger than we would normally expect. So what happened in the Loddon River? If we look at the Loddon River on a year-by-year basis, here we are looking at the annual rainfall-runoff relationship, with rainfall on the x-axis, runoff on the Y-axis, and each individual year is a point and we've coloured them by pre-drought and drought in this left-hand plot. So pre-drought, we've got lots of different dots for different years. We've got a nice blue line through those dots to give us a rainfall-runoff relationship. So wet years we'd expect more runoff, dry years we'd expect less, and in the middle about here. We can also plot on this diagram what occurred during the drought, and we have here the dots for the drought years and the line through those dots for the drought.

And we can see rather than following this blue line down to the dry period and producing less runoff as expected, the actual runoff ratio for the Loddon River has actually decreased and has shifted to a lower level. So for the same amount of rainfall, say 700 millimetres, the Loddon is now producing less runoff, significantly less runoff than we would've expected under pre-drought conditions. We refer to this as a shift in the rainfall-runoff relationship. If we look at the post-drought situation, so here we've got the pre-drought relationship in blue, post drought in this yellowy colour, we can see that the post-drought years are still plotting below the pre-draught line and the line for the post-drought is actually offset from the pre-drought line, and significantly so. So this catchment shifted in the drought, and has not recovered. It's still behaving as if it's producing less runoff than we would expect.

If the catchment didn't have a shifted relationship, and this pre-drought line applied to the pre-drought, drought and post-drought period, that would be referred to as a stable catchment. If the relationship shifted during the drought but then recovered back to the blue line post-drought, we would refer to that as recovered catchment. So if we now have a look at the spatial distribution of our catchments across Victoria and see how they've responded during and after the drought, we can see that in the eastern catchments in the highlands in Gippsland, we've got lots of stable catchments. So in these catchments, the rainfall-runoff relationship pre-drought, during the drought and after the drought was exactly the same, there was no significant change in the relationship. So in these catchments, the runoff we received during the drought was the runoff we would expect from having some dry years.

The green catchments on the other hand, they actually shifted their relationship during the drought, and have then recovered since the drought, so they produced less runoff than expected during the drought, but then are now producing the runoff we would expect post-drought. Whereas the red catchments, they shifted in the drought and they have not recovered. They are still producing less runoff than we would expect even though the rainfall has returned back to normal.

Now we looked at this phenomena through two different methods, and the second method is basically a hidden Markov model method, which I won't go into the details of, but basically it has multiple different states that the catchment could be producing runoff in. So it could be producing runoff in a normal state or in a low-flow state. And we can track over time the proportion of catchments, the percentage of catchments that are producing in a low-runoff state, effectively a shifted state. And we can see in '82, '83 we had some more catchments producing less runoff than expected. But once the drought gets going in '97, we start to see an increase in the number of catchments that are actually in a low-runoff state, right, and it peaks at the end. Then the drought breaks, we get a reduction in the number of catchments in a low-runoff state, but then it's fairly stable thereafter through to the 2016 when the analysis ends.

This was on an annual time step. When we do it on a seasonal time step, we basically get the same story. So we've got an increase in catchments in the low-runoff state, and then a fairly stable number after the drought has finished, which is indicating that we've basically got about a third of our catchments in Victoria are still in a low-runoff state as of the end of 2016, that's eight years after the drought. So normally you would expect that a catchment might have recovered by now, eight years later, but for about a third of our catchments they have not and in an analysis we don't show, we basically are seeing that those catchments that are still in a shifted state are not showing any sign of recovery soon.

So what are some of the features of the catchments that are showing rainfall-runoff relationship change? The main features using a multi-model inference technique, was pre-drought climate. So the climate that the catchment experiences prior to the drought is a good indicator of whether it'll shift or not, and dryer catchments are more vulnerable to shifts.

Also the relief of the catchments, so how steep or flat is the catchment? Flatter catchments are more vulnerable to shifts, and also the catchment moisture storage. How much moisture can this catchment hold? Catchments with more moisture storage seem to be more vulnerable to shifts. So when we combine all those items into a multi-linear regression, we could basically find that if you take into account the smoke and the humidity index or how arid a catchment is, that explains 75% of the variants in the stream flow anomaly during the drought.

If you added the unconfined aquifer thickness, which is a catchment moisture storage metric, we get that up to 81% of the variance is explained. So dry, flat catchments with high-moisture storage seem to be more susceptible to rainfall-runoff relationship changes during the drought.

If we have a look at what sort of processes might be occurring, that could be leading to these sorts of changes, we can see here, we are looking over time at the average fraction of days in cease-to-flow conditions at a catchment. And we've coloured these catchments by whether they recovered, shifted, or were stable. And you can see that the stable catchments basically didn't have much change in cease-to-flow behaviour during pre-drought, during the drought, or after the drought. They were stable. The recovered catchments started to have an increase in the cease-to-flow conditions during the drought, and cease to flow basically indicates that the surface water and the subsurface moisture have disconnected.

So if there's no base flow coming into the stream through the subsurface, it's totally disconnected. And we can see that the shifted catchments have had a dramatic increase in cease-to-flow conditions during the drought, which has then dropped after the drought, but then returned to a fairly high level post-drought. So pre the drought, catchments that were susceptible to shifts were actually ones which had high cease-to-flow conditions even before the drought, and that increased even more during the drought.

The final bit of analysis we did is we looked at the additional reduction in stream flow. So previously we were looking at stream flow anomalies where we were looking at the mean runoff during the drought, relative to the mean runoff prior to the drought. But during the drought, if you have a stable rainfall-runoff relationship, you actually expect for a reduction in rainfall, you'll have a reduction in runoff, and that's what you'd expect.

So we were interested here in what was the additional reduction between B and C because of the change in the rainfall-runoff relationship? And if you plot that additional reduction in stream flow as an anomaly relative to the pre-drought mean across Victoria, we can see that in the eastern catchments where there were mainly stable rainfall-runoff relationships, there's not much of a reduction in addition to the rainfall-runoff relationship change, it's basically zero or five to 10%. Whereas if you get into the centre and the west, we're talking about numbers in the order of 20 up to 40% reductions in addition to the fact that it's just dry, we're in a drought.

So the reductions in runoff due to the change in rainfall-runoff relationship are non-trivial and quite substantial. And in a parallel bit of work with [inaudible 00:26:50] and DELWP, those values were extrapolated across the state where we had data, and we can see a map of that in the synthesis report.

In summary, the findings and the implications. The key things are rainfall-runoff relationships can change during prolonged dry periods and significantly less runoff is generated for a given rainfall. Now, this was the first time we'd actually seen this in our catchments in Victoria. So long droughts can change the relationship, and you end up with less runoff than expected. The relationships don't always recover after the drought. So we're finding that about a third of our catchments are still in a low-flow state and they're not looking like recovering soon. How long that will persist for remains an open question.

Drier, flatter catchments are more vulnerable to shifts and there's processes potentially related to surface water, subsurface water disconnection that might be explaining that. And future projections, runoff projections say under climate change scenarios will need to use models capable of reproducing relationship shifts. If you have a model that doesn't reproduce that shift, you're going to estimate too much runoff. You'll end up with more a projection of more runoff than you'll actually have if your rainfall-runoff relationship shifts under a drier future, and the projections are indicating for Victoria that we will be having a drier future. So thank you. That's all I'd like to present, and thank you for listening.

Francis Chiew:

Hello everyone. Well, my name is Francis Chiew, and I will be presenting the hydro climate projections research on behalf of the CSIRO research team summarise in Chapter 4 of the Victoria's Water in Changing Climate synthesis report.

Well this first slide shows for context the annual rainfall and model runoff series average across Victoria. Like most parts of Australia, there is a very high variability in the rainfall and runoff, where the runoff in wet year can be more than 10 times larger than the runoff in drier years. So this next slide illustrates the projected changes in the future rainfall and runoff expressed as changes to the average conditions. We do know that the future will be hotter with more very hot days and more extreme fire danger weather days, and the higher temperature will also increase potential evapotranspiration demand. Rainfall is likely to decline, particularly in the cool season. And this decline in rainfall will be amplified in the runoff, particularly here in Victoria, because a large proportion of the rain falls in winter and early spring. So it's important to note also that the variability will remain high, so we'll still have wet years or wet not years, but the dry periods that we encounter will become more frequent.

This next slide shows an example of the run of projections. So this is developed in the Victorian Climate Initiative. So these projections come from hydrological modelling informed by the change signal from the 42 global climate models used in the IPCC or Intergovernmental Panel on Climate Change fifth assessment report. Now, you can see from the plots the immediate result shows significant decline in the future runoff, but there is also a big range of uncertainty in the projections, largely because of the uncertainty in the future rainfall projections.

Now, we believe that these projections continue to be the most appropriate for the water sector in Victoria, and you can consider these as changes or projected changes relative to post-1935 averages. So the DELWP Victoria guidelines provide more detail on using these for water resources planning.

Now this slide here shows the modelling components in projecting water futures, from interpreting change in global average temperature from different emission scenarios, and then modelling the global and regional climate responses to these changes in a temperature, and then the downscaling, in particular rainfall, to the catchment scale so that we can run them through the hydrologic models.

Now, each step has its own inherent uncertainty and these can be compounded through the modelling process. The biggest uncertainty that we see comes from the rainfall projections. This example here shows the range of projections from the 42 global climate models, and this uncertainty or the range in these rainfall projections gets amplified in the runoff projections. So it is a big challenge, not limited to just Victoria or Australia, to interpret and communicate these projections, and then to use them properly to inform adaptation options and different approaches are certainly used in different parts of the world.

Now, the dynamic downscaling that is converting the cost, special resolutions simulations from the global climate models to the final-scale simulations, can obviously potentially add value, particularly in coastal areas and across mountain ranges. So the example here shows dynamic downscaling from the DELWP VCP19, Victorian Climate Change 2019 product, from the CCAM dynamic downscaling model. So notable and worrying futures both from this downscaling is the enhanced drying that we see in the westward slopes of the Victorian Alps, which is a significant runoff-producing area.

Now nevertheless, although the dynamic downscaling continues to improve, there is significant bias in the downscale rainfall, and this needs to be robustly bias corrected to fully utilise its value for hydrologic application. Now, this can be challenging as many features of the rainfall that influence runoff generation needs to be robustly biassed corrected. So some of the research that the Victorian Water Climate Initiative is working to are listed at the bottom of the slide, and this includes bias correcting multi-day rainfall totals or events, and bias correcting the spatial rainfall characteristics, which if you don't do this properly or robustly, we will underestimate the catchment runoff.

So given the various approaches for perspective, we show here the annual rainfall and runoff projections from the different projection sources. And this example comes from a catchment on the Goulburn River Basin. The first series of dots that you see here are the rainfall and the model run of projections from the 42 global climate models, or GCMs, so the ones recommended in the guidelines. And the 10, 58 and 90% values are also shown here.

Now, this next series of six dots then show the six host GCMs that provide the boundary conditions for the CCAM downscaling in VCP 19, which I mentioned in a previous slide. Now the orange dots show the raw outputs from the CCAM, and these are different and they indicate that the projected decline in the dynamic downscale rainfall are generally larger here than the projected decline from the host GCMs above. Now, the next series of grey dots then show the bias correction that we apply. This resulted in even slightly drier and no change signal compared to the raw downscale rainfall.

Now for comparison, I've shown here the next series of dots show projections from another dynamic downscaling model. So this comes from the WRF model, or weather research forecasting model, from the NARCliM product in New South Wales, and this again show where the projections from the above CCAM downscaling.

So I think the take-home message from this is that different projection products and methods do not necessarily converge to narrow range of change. Therefore, it is very important to understand the projections and to interpret them for the context of the application. And the DELWP Victoria guideline report provides some guidance on how to do this. So I think in the previous slides, we discussed how changes in the climate inputs are translated to the hydrological model, and then amplified in the runoff responses. Now this penultimate slide shows that there are also limitations in the hydrological modelling approach itself that we need to overcome to extrapolate models to properly or robustly predict the future. Now this is largely due to the changing rainfall-runoff relationship that we see, as we moved to a future conditions, under hotter conditions, enhanced CO2 concentration, and longer dry spells that we have not seen in the past, that we used to develop these models.

Now this is an active area research in the VicWaCI and research elsewhere, Millennium Drought dataset and pre-drought and post-drought data do provide an ideal test case for research, not only here but also for research overseas. And some of the leading work on these are summarised in Chapter 3 of the synthesis report.

So in summary then, I think I've shared with you some results from the hydro climate projections research in Victorian Water and Climate Initiative. So we know that the future runoff in Victoria is likely to be lower because of the projected decline in cool season rainfall and higher potential evapotranspiration from the higher temperatures, while given the large range of possible common futures, what resources planning should consider these? What range of possible futures, and understanding of Victoria's water future continues to improve due to research in initiatives like Victorian Water Climate Initiative. Now, because of the possibility of a large range of possible futures, assessments focus on the systems approach that characterise resilience to climate inputs can help provide some insights and provide a foundation for considering risk versus reward of adaptation options.

Now you can find more details of these in the DELWP report on Victoria's Water in a Changing Climate Insights from the Victorian Water and Climate Initiative, and from the guidelines report, which provides some recommendation or guidelines on how to use outputs from the Victorian Water and Climate Initiative research. Thank you very much.

Rebecca Lett:

Hi everybody. I'm Rebecca Lett, Senior Project Officer in the Hydrology and Climate Science team of DELWP's Water and Catchment Group. I'll be facilitating the Q&A this afternoon. I hope you enjoyed the presentations by Pandora Hope of the Bureau of Meteorology, Murray Peel of the University of Melbourne, and Francis Chiew of the CSIRO. Now obviously there's a lot of research to absorb, and so we do recommend that you read the Victoria's Water in a Changing Climate report. It's a really useful document for water resource planners and for anybody in the water sector who is seeking a deeper understanding of how Victoria's climate and hydrology has changed, and how it is projected to change in the future. The report is available for download on water.vic.gov.au/VicWaCI. So don't worry if you didn't catch that, we're going to be putting a link in the chat window for you to copy.

And if you were unable to hear the audio in the opening video, again, don't worry. You can view the video again if you wish, on the VicWaCI website also. So we have a bit of time now until 2:00 PM, so I will be putting a few questions to our researchers who are joined now by Geoff Steendam, Senior Manager of the Hydrology and Climate Science team. And remember, we are recording today's session and the recording will be made available on the VicWaCI website. And if you have questions, type them into the Q&A box. But if we can't answer them all today, please email any further burning questions through to the team at hcs.team@delwp.vic.gov au. And it's really great that we've already seen a few questions come through during the presentations, and presenters have been busy already answering some of your questions, but please the more the merrier, please keep sending through your questions.

We'd love to hear what is of interest to you. But I'm going to start with a general question to all our researchers and Geoff. Actually two questions. We had two questions, they're both great questions, we couldn't decide which one to ask, so we're going to ask them both to all of the researchers and Geoff. What is the most surprising finding from the programme in your opinion? And also, what do you feel is the most important finding from the programme that you feel the water resource stakeholders in Victoria really need to be aware of? So what is the most surprising thing and what's the most important thing for water resource stakeholders to know about? I'll probably throw to Pandora first, seeing how she was our first presenter.

Pandora Hope:

Thanks, Rebecca. I think for our research, certainly on the weather types, if you look at that rainfall decline and what might be causing it, we would immediately think there'd be fewer rain-bearing systems. But actually we found that there weren't a reduction in the number of fronts, it was actually how much rainfall came from those fronts. And I think to our group that was pretty surprising and very interesting, and something we really want to explore a bit further. And from that, we can think about the work that Murray presented, that reduction in runoff that you get for the same amount of rainfall, and we started to look at how the weather systems might be implicated in that or not, and actually found that when you do have fewer of those kind of widespread showery rain events associated with fronts, they really wet up the catchments and help that runoff flow.

So a reduction in rainfall from those is actually having an impact, along with a whole heap of other factors contributing to that runoff decline. That's not the biggest finding you could probably take from this if you're planning into the future, but I'll leave that to some of the other researchers to answer.

Rebecca Lett:

Great, thanks Pandora. I guess Murray, you were the second speaker, so you're up next. Murray, what is the most surprising and the most important finding?

Murray Peel:

Thanks Rebecca. I would say that actually just slightly contrary to my video, we had actually seen rainfall-runoff reductions previously in Margarita's PhD, and looking at them across Victoria, the numbers that we saw were of a similar magnitude, so we saw quite a lot of changes. The surprising thing I think for us, was just how many of our catchments hadn't recovered eight years after the drought had ended. So the previous assumption was... Well, most people would assume that after a drought ends, your rainfall-runoff relationship might return back to normal. And it did in some of our catchments, but there was actually quite a few, about... a third of our total catchments across Victoria, were still not showing a recovery in their rainfall-runoff relationship after the drought.

Now, what are the most important things from a management perspective? Probably the most important thing is your rainfall-runoff relationships can actually change if you have a prolonged drought like we just had, and that will influence how much water you're likely to get from your catchments on the negative side, if it's a drought. And don't assume that that relationship will automatically bounce back after the drought, because we are seeing that that is not the case, particularly in those western Victorian catchments. It would be fascinating to get hold of the last four years' data from 2017 to 2020 and see how many of those ones that were shifted are still shifted. But that's for future activities.

Rebecca Lett:

Thanks very much Murray. Over to you Francis, your turn?

Francis Chiew:

Yeah, hi Rebecca. I think Murray and Pandora has covered a lot of it quite nicely. I don't have a top pearl or top price or whatever here. I think the broad knowledge across all the research areas is largely similar, but I think what we've gotten out of the research is we've got more confidence in the knowledge, because there's more data now, and further interpretation of the data set and some analysis we've done. So we know that the future will be hotter and the future will be drier, but uncertainty range will... Well, the uncertainty in the projections will remain. But what we do have now is better knowledge of that, and better understanding of the range of possible outcomes and more tools and more projection products that are available now. So one of the good things for Victoria I suppose came from the VCP 19 also, which is from another part of DELWP, which is the downscaling products.

What we've done in with VicWaCI is developing the robust bias correction methods that can translate that for application in hydrology. So that's very important in that context also. You heard about the hydrologic non-stationary research and ongoing research either trying to build or develop that models to be able to represent them. And one of the things that VicWaCI has done is also to put into context different projection methods and coming up from a different projection products, and then the guidelines now providing some idea about how to recommend and guidance on how to use that. I think all in all, across the whole programme or the whole initiative, we're putting ourselves in a good position with all this knowledge to help, to fully improve our knowledge as well as for the next-generation projections, especially with new knowledge in climate science and hydrology modelling science, especially with the upcoming products from the [inaudible 00:45:45] or the IPCC AR6 type projection products. And our climate brothers and sisters elsewhere across Australia are working with possibly coordinate downscale experiments. So all these will put Victoria in a good position moving forward.

Rebecca Lett:

Great. Thanks Francis. And lucky last, Geoff, it's your turn. What do you think is the most surprising and the most important finding from the programme?

Geoff Steendam:

Great, thanks Rebecca. I guess just following on from all those great comments there and the great presentations, there's a whole lot of really important findings, I think, across all of this research. There's a lot of different research projects, and lots of different themes that were investigated. So it is very hard to pick out a couple of things, but just to mention I guess, two things. I think one of the challenges we have in the water sector is we had that in 1997, obviously start of the Millennium Drought. And there is this question over how much is that a step change in our climate or not? And obviously we've made a lot of incremental gains in knowledge through this programme about better understanding that, and a given a lot of the decisions we make in the water sector, that five, 10 year horizon can sometimes be often more important even for some things, than say sort of looking through the decades out into the future.

I think that understanding that we can get around our current condition and the impact of climate change on us today is one of the really important areas, but also the shift in runoff response. Obviously it's an active area of research still, but then how that feeds into the projections Francis was talking about, is an important gain through this programme and something we'll be looking at into the future too.

Rebecca Lett:

Great. Thanks Geoff. Don't go away. The next question's for you as well. How are we going to take all of this really important information and make sure that it's being used by the water industry to improve decision-making?

Geoff Steendam:

Yep, thanks. I think Francis mentioned in his talk the guidelines, so the guidelines that DELWP developed for assessing the impact of climate change on water availability in Victoria. So that's really the most tangible example, I think, of how we take all this science and then help with that translation of the science through to application because there is a big... It's very challenging going from research through to application. And so I think that the guidelines that we produced and were released in December and available on the website and we can put a link up, I think that's a really... And we've found that it has been a really valuable way for the water sector to easily implement this science and knowledge. But I think that is still only just one example. I think there's a lot of applications from a lot of the different areas of this research. And so we'll be continuing to work with all of our stakeholders across the sector in applying it over the coming years, and we always welcome help and the support of our stakeholders in doing that as well.

Rebecca Lett:

Great. Thank you Geoff. Now I'm going to throw back to Pandora. There was a question earlier in the chat about whether the information that you presented on increases in rainfalls extremes were based on single sites or whether it was an amalgamation of information from multiple sites. So you might just want to clarify that. And we also have a very interesting question from Jasmine. Do we know whether a dry landscape contributes to the observed reduction in rainfall? So IE less evaporative sources, or does most of our moisture come from the ocean?

Pandora Hope:

Quickly, it was from single sites. We did a good analysis on the data quality of the high-intensity rainfall measurements that were available across the state. And those eight sites stood out as having a longer high-quality record. Further analysis we've done, we have used a conglomeration of all available data simply to get that regionalization of signal, because we are comparing against other variables like dewpoint temperature, but that's new research to come.

Do we get much moisture recycling? Is the question I heard. So is there much water coming from the land surface into the atmosphere and then being rained back down onto the same bit of land? And the answer is, in Australia in general, and certainly in Victoria, not that much. Most of our moisture comes from the oceans, and in summer it can be enhanced by the local conditions. And that signature is, we think, trending to happen more often. So there's new research happening in the Centre for Excellence for Climate Extremes on this, and we're collaborating with those people using our weather type data sets to have a closer look at this at the moment.

Rebecca Lett:

Great. Thank you Pandora, and thank you for your excellent presentation. Now, I'm going to ask question of Murray about your research and how it relates to groundwater. Because this is actually, we had a seminar series last year and we always got a lot of questions about the interaction between surface water and groundwater, so I think the people listening to today might be interested in this question. Is the continued reduction in runoff somehow related to groundwater deficits in the arid zone? EG, is there now more recharge rather than surface runoff?

Murray, you're on mute.

Murray Peel:

I am on mute, apologies all. Technology hitch there, thanks Rebecca. So with that question, we've recently had... a perceptual model workshop on what we think is going on in these catchments during the drought. And certainly groundwater is one of the processes that we've been looking at. In a paper that we've got under submission at the moment, we've actually been looking at a range of different things. One is, what sort of groundwater traces do we see in catchments with shifting behaviour?

And in quite a few of them, the groundwater's decreasing as well, which is basically indicating the recharge is actually not enough to sustain groundwater levels like it used to. So rather than the groundwater suddenly taking more recharge than it used to, we're actually having less recharge in these catchments because the groundwater's decreasing at the same time as the runoff's been decreasing. So what we suspect is that it's actually the unsaturated zone or the vadose zone is actually expanding, which could be causing that. However, that is still very much the subject of vigorous research in a follow-on project with DELWP and Melbourne Water and CSIRO within an ARC linkage project, which is currently in progress.

Rebecca Lett:

Well, I can't wait to find out about the results of the ARC linkage project.

Murray Peel:

Transcript for A system’s approach to understanding climate change impacts on water webinar

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