Transcript of the Victorian Water and Climate Initiative webinar

Alice Ritchie:

It's in progress at the moment. Just for the recording, our webinar today is in our climate webinar series is on the Victorian Water and Climate Initiative, looking into climate impacts on water supplies and availability, and risks to water resources in Victoria. Today, Jeff will provide an update on the Victorian Water and Climate Initiative. The initiative supports research into the impact of climate change and climate variability on Victoria's water resources.

Alice Ritchie:

This includes three distinct but related research projects undertaken with the University of Melbourne, the Bureau of Meteorology and CSIRO. Geoff Steendam manages the hydrology and climate science team in the Victorian department of environment, land, water and planning. The team serves as a knowledge broker for the Victorian water sector, investing in targeted research and working with the sector to help apply the knowledge. Geoff has worked in water resource planning roles in the department for more than 10 years and previously worked for consulting engineering firms in Australia and the UK. I will now pass over to Geoff Steendam from the department of environment, land, water and planning. Go for it, Geoff.

Geoff Steendam:

Excellent. Well thanks Alice, and thanks to the team in Agriculture Victoria for the chance to present today. We really appreciate it. Like a lot of people I'm working from home, so hopefully we don't have a couple of young kids come in the door, but so see how it goes. Sorry, I'm just trying to change slides. Yes, here we go. So just an overview of the talk today. So I'll start. So it is all about the Victorian Water and Climate Initiative, but I'll start with a bit of context for the research program so you understand where it's come from and why we're doing it.

Geoff Steendam:

And then I'll talk through the three main components of research, that's the climate research with the Bureau of Meteorology, hydrology research with the University of Melbourne and then climate and water projection research with CSIRO. And then I'll just finish off briefly talking about application and next steps. So just firstly in terms of the context of the research program. So the team, so the hydrology and climate science team we sit in department of environment, land, water and planning, so DELWP and in the water and catchment group of DELWP.

Geoff Steendam:

So the Victorian Water and Climate Initiative is one of the big projects that we lead and manage. But we get very involved and then applying the findings that come out of that program and from the science more broadly to all of the policy and planning activities that occur across the different parts of the water sector. We work closely with regional delivery partners like water corporations and catchment management authorities across the state, and also provide them tailored guidance. And so I'll talk at the end about some guidance document that we provide as well.

Geoff Steendam:

So we're in a different department to Agriculture Victoria, but there are a lot of connections between the work of the teams and also connections between the scientists and the researchers as well. And our work is more focused on the longer term understanding of water availability rather than the sort of shorter term outlooks like say, seasonal forecasting. So this research, the Victoria Water and Climate Initiative is part of the Victorian government's water plan Water for Victoria, which was released in 2016.

Geoff Steendam:

So the history of the research program so there's really since the middle of the millennium drought in 2006, the water sector in Victoria has been investing in this kind of research. So that started with the Southeast Australian Climate Initiative which covered Victoria and the Murray-Darling basin. That was followed by the Victorian climate initiative. And then now the current Victorian Water and Climate Initiative. And so through the course of the program, we're trying to put out outputs and share findings as we go. But it's really during this final year that all the findings are coming together as part of a synthesis report that we'll put out at the end of this calendar year.

Geoff Steendam:

And I guess why the water sector invests in this research, most of the water sources in Victoria are climate dependent. And so there's a strong interest for the water sector to understand the impacts of climate, climate variability, climate change on water availability, and also understanding the hydrology too because really climate presents a big opportunity and risk for the water sector. So the more we can understand it, the better we can make informed policy and planning decisions. And also through the current issue we're trying to get more map-based products. And that aims to make the work more accessible, and also to provide more regional information from the research that's being done.

Geoff Steendam:

So now, just onto the first component research or the climate research that's being led by the Bureau of Meteorology. So this really has a rainfall focus because rainfall is really the primary driver of water availability. So there's three main projects I guess within this climate research. So I'll talk briefly through these, but the first ones really look at how much rain we get from different weather systems across Victoria. Understanding how that's changed over time, and then how it might change into the future. And then what are the physical processes driving those changes in rainfall?

Geoff Steendam:

Second project's looking at what our current climate baseline is. So how much, for example, does the experience we've had since 1997 the start of the millennium drought, how much does that reflect a new normal? That's one of the big questions for the water sector. And then the third project is looking at increases in extreme rainfall, is trying to better understand how extreme rainfalls could change. So temperature is not a big focus of the research program. But I just wanted to just show this slide of annual temperature across Victoria, just to make the point that temperature, even though it's not the primary driver, it's still obviously very important for water availability, it affects water demands. So not just consumptive uses like from crops, but also from forest catchments too.

Geoff Steendam:

Because temperature is an important driver of evaporation and also transpiration from catchment vegetation. And as we can see, temperatures have been going up across Victoria. So by about a degree over recent times. So now into rainfall. This is looking over the past 30 years, and so splitting Victoria's rainfall up into what's called the warm season and the cool season. And so maybe just starting with the cool season at the bottom there, that's the cool season is really that's just the cooler months of the year, if you like. So that's the April to October period.

Geoff Steendam:

And as you can see from that map of Victoria at the bottom there, the reds indicate that we've had below average rainfall and in some places very much below average rainfall over that cooler time of the year over the past 30 years. Whereas the warmer time of the year, so from November through to March, that's much more of a mixed signal. And so in the North wetter in some places, whereas drier in the South. And so the reduction in that cool season rainfall is a really important one for water availability.

Geoff Steendam:

That's the time of year when catchments didn't really produce more runoff because temperatures are lower, so catchments aren't as thirsty. And so you're getting more of your rainfall that's becoming runoff. It's also the time of year when most places get the bulk of our rainfall as well. And so understanding what's going on there with those declines is really important for water availability. So just looking still at those cool season declines, so that's April to October but this slide just maps that out for each year. Comparing it to sort of rainfall and normally just comparing it to these 1961 to 1990 average.

Geoff Steendam:

And you can see that obviously a lot of variability there. But over recent times typically over the cooler months we're seeing a deficit. So that's really particularly the millennium drought. But then even after the end of the millennium drought, there's still those declines we're seeing in that rainfall during those cooler months of the year. With the exception there of 2016, you can see at the end of the graph. A lot of the research is trying to understand what's driving those changes, and the research has found that over past decades has been a decrease in the frequency of low pressure systems over Victoria, so we're getting low pressure systems less often, particularly during the winter months.

Geoff Steendam:

And we've also got less rain from each of those low pressure systems when they do come through. And so that's quite a concern obviously for water resources because that's the important time of the year for getting runoff from water and an important time for water availability. And the research has found that those changes in the courses and rainfall and the reduction in rainfall from those low pressure systems is associated with broader changes in climate that's going on, including tropical expansion. So where we're getting these weather systems tracking a little further South.

Geoff Steendam:

And so now just to mention the work that the Bureau is doing on mapping, we'll analyse here in mapping how much rain we actually get from different weather systems. So this is just a schematic to I guess introduce that. The work is still ongoing and so it's really through the synthesis report at the end of the year where a lot of these results will become available. But this schematic is just showing three example weather system types. So frontal systems in the blue, thunderstorm dominated systems to the North, and then East Coast slows more to the East.

Geoff Steendam:

And so what the Bureau is doing is actually mapping how much rain we get from those systems in all of the parts of Victoria, and how that changes seasonally and then any trends in those systems over time, and then what's projected for the future. So I think it would be really very interesting and quite powerful piece of work. So the last climate research area I want to talk about is extreme rainfall. So we know that the rainfall during the cooler months of the year and rainfall as a whole expected to increase into the future, but extreme rainfall is expected to go up.

Geoff Steendam:

But it's still joining those two together is maybe not very clear how much extreme rainfall, or when scientists say extreme rainfall increase what exactly do they mean? So we've done a piece of work with the Bureau to try and get the clearest explanation of that, that we can. So we put out this fact sheet on our website a little while ago, and that work has really shown these four key findings here. So it's really the durations we expect to be those very short durations. So less than an hour where we'd expect to see increases in intensity. And it's during the warmer months, particularly in summer when we'd expect to see it, and for those rarer events as well. But of course it depends where you are, and the season as to how much we will see these changes.

Geoff Steendam:

The Bureau is also analysing pluvio rainfall data across Victoria to actually understand how much has we already seen some of these changes and they are finding consistent with these points here that it is those short duration events particularly in summer where we're seeing the increases in extremes. But from a water validibility point of view, given the nature of the extremes we're talking about, it doesn't compensate for the overall reductions we expect in rainfall.

Geoff Steendam:

So now on to the hydrology research, and so this work is being led by the University of Melbourne. And so it's really looking at how stream flow is changing under a drying climate, and particularly how catchment response is changing. So when we look back at records these are for streamflow gauging sites across different parts of Victoria. Just annual rainfall, sorry, annual streamflow there. And you can see there's a lot of variation, particularly in some parts of the state more than others. And the solid black line is showing prior to the millennium drought. So on the left of those plots, what the average was at that period.

Geoff Steendam:

And then the solid line on the right hand side of the plots is what the average was since 1997 the start of the millennium drought. And so you can see there some really significant reductions in streamflow particularly for the Wimmera. And even though the 2010 floods was the end of the drought, and really in all these systems streamflows since then have still been pretty disappointing. So just mapping that across Victoria. This is just to give a broader sort of spatial picture.

Geoff Steendam:

You can see that there's many sites, well all of those sites there as you would expect over the past 20 or so years have experienced declines in streamflow. But there's quite a strong spatial signal there with particularly the catchments to the North and West experiencing greater reductions. And I just wanted to now just sort of talk through an example catchment because even though we would expect to see reductions, we didn't actually expect to see reductions of this magnitude. And so what we've actually seen is a greater reduction in streamflow than we would have expected given the reduction in rainfall experienced.

Geoff Steendam:

And so I'll just work through an example for a gauge which is this one here in the Loddon catchment. And so this catchment is Jim Crow Creek and the gauging location is at Yandoit. And this catchment headwaters is up at Hepburn Springs here. And so I think the catchment area is about 166 square kilometres. So just to show some of the data that's been recorded at that location. So this is data prior to the millennium drought, so prior to 1997. And what this is, is precipitation across the horizontal axis and then stream flow on the vertical axis.

Geoff Steendam:

And so this is annual data, so there's a dot for each year. The records for this gauge starts in about 1955. So this is data from 1955 through to 1996 a dot for each year. So given a certain depth of rainfall across the catchment as a whole, you can work out the precipitation and then you can using the streamflow gauge data, work out what that corresponds to in streamflow. The unit here is millimetres across the catchment. And so quite a strong relationship you can see there a lot of scatter still, but still quite a strong relationship.

Geoff Steendam:

You can fit a relationship through there. And you can see that obviously it's not a linear relationship, so new year is where you're getting much higher amounts of rainfall, you're getting much larger amounts of streamflow. And so you're getting some more of that rainfall that's being converted to streamflow. During the drought obviously we're getting less rainfall, so shifting sort of to the left of that. But if we plot the points for the millennium drought here in orange, you can see that even though they are more to the left because the rainfall for those years is lower, they're actually sitting below or almost all those points are sitting below that relationship.

Geoff Steendam:

And so what we've experienced in this catchment is a reduction in that rainfall runoff relationship. So then if we look at the year since the end of the drought, or at least some of those years since the end the drought, you can see that still is somewhat following that relationship that we had during the drought. So even though in some years we're getting better rainfall than we had during the drought, the streamflow response has still not recovered. So then just to give an example to work that through a bit. So the long-term rainfall for this catchment is a bit off 800 millimetres.

Geoff Steendam:

So then if you look at the old relationship pre drought, you could expect on average a certain quantum of streamflow. But then looking at that more recent relationship that we've experienced there, you're getting for that same amount of rainfall across the catchment, you're actually getting significant reduction in streamflow so in the order of 30% or so in this example. So this is a real concern, and we're doing further work to really understand where is this being observed, where is it happening? And also why is it happening?

Geoff Steendam:

So firstly, the where, so this is mapping where across the state this is occurring. So this is using all the gauge data that we're able to use with this analysis. The blue catchments in the great divide there are shown as stable. And so that's really where there's been no statistically significant shift in this relationship, whereas for the red and the green catchments in those catchments, there was a statistically significant shift during the drought.

Geoff Steendam:

The green ones have actually recovered since the end of the drought, whereas the red ones are still operating as though they're on that different lower rainfall runoff relationship. So we want to better understand why this is occurring. And we don't actually have the answer to that yet. We're trying to find out as much as we can through the current research program. There's lots of different ... Everyone we talked to has ideas about what could be driving this. It could be related to groundwater declines impacting on streamflow.

Geoff Steendam:

It could be related to vegetation catchment vegetation using more water. So yeah, it's still an active area of research. We've put out a fact sheet on this and so this is available on our website. And we're still trying to also just better quantify the magnitude of the changes. And so we can use that and share that with all the people across the water sector. So the last area of research I want to talk about was climate and water projections. And so this is being led by CSIRO, and this work is really around trying to better understand the range of projections for future climate and future water availability, and better understand the uncertainties in those projections so that we can for the water sector be very informed users of projection information to make the best use of that and understand what they mean and how we should be using it.

Geoff Steendam:

And so this is really talking about future decades in contrast to say seasonal forecast. For the water sector, obviously we really want to know where could things be headed so we can prepare. This is some projections that were developed by CSIRO as part of the earlier Victorian Columbia Initiative. They show different maps of the state, blue being where there's an increase in predicted increase in runoff or streamflow. The redder colours being where there's a projected decrease and there's working across the top, there's low, medium and high. And so that's really just to represent that range of different projections given there is that very large uncertainty in projections of the future.

Geoff Steendam:

This is really trying to represent that range so we can get some insight into what that range looks like. The two rows, the top row is that the year 2040, so 20 years or so into the future, and the bottom row is for the year 2065, so about 45 years into the future. And even though there is red and blue here in the sort of best-case example for the low in 2065, there's many catchments and the great divide there where there's no change from the long-term record. But there's even in the Southwest some reductions, even in that best case.

Geoff Steendam:

Whereas the vast bulk of the projections suggested decline and in some cases quite significant declines. So really there's multiple lines of evidence that give us confidence that it is very likely that we'll get reductions in streamflow into the future. So more recently there has been projections developed called the Victorian Climate Projections 2019. And so this is a set of dynamically downscale projections. Although these projections don't include projections of changes for streamflow and runoff. But we are looking at these projections to see what they could mean for the water sector and how we could potentially use them for water sector planning.

Geoff Steendam:

So I won't talk through this one in any detail, but I just wanted to show this to I guess highlight there is a number of different steps to developing projections, and each of these steps has its own range of uncertainty if you like associated with it. And so ultimately there is quite a broad range of projections that are all quite possible. So a lot of the research that we've invested in the water sector is really trying to understand that range of projections, how it fits with the physical science, how it fits with the trends of what's been observed so that we can use them in the most informed way that we can.

Geoff Steendam:

Also just to point out too, that even this is really about how we understand impact on streamflow in the upper catchments. But then if you're wanting to understand, well, what does water availability in the upper catchments mean for those certain water product or water entitlement water share, or water license downstream, or urban water entitlement. You really have to apply the water system models to then see what the changes upstream mean as you work down through the system.

Geoff Steendam:

So now I just wanted to finish with a couple of ... Well a brief example of application and then just the next steps. And I might just briefly summarise some of the earlier points here. So essentially we've seen those reductions in the rainfall during the cooler months. It is possible, we may see increases in the warmer months, but because of the importance of the cooler months, the rainfall in the cooler months for runoff in the cooler time of that year, we do expect that those declines in course in rainfall will dominate, and that we'll see less water availability as a result.

Geoff Steendam:

We're seeing that shift in runoff response too. And so that's really an additional impact we need to better understand and take into account. And then when we look at overall the projections for the future with those multiple lines of evidence, we do have confidence that there would be declines we can expect to see into the future. So now just on application, I mentioned the guidelines earlier. So this is a set of guidance that the department prepared in 2016 and provided to water corporations to assist them to take the science and apply it to their planning and decision making.

Geoff Steendam:

There's quite a bit of content in these guidelines, but one of the points in there is really just that the past no longer reflects conditions today. And so we've seen really a shift in the probabilities, and so obviously there's still a lot of variability, but the chances of getting warmer conditions and less streamflow is higher now than in the past and we expect that into the future. One of the challenges for the water sector is what is our baseline, what is that current situation? And so a lot of the research is trying to go into better understanding there. Better understanding how much the conditions since 1997 may or may not be our new future from here. And I was interested to see there's an ABARE report I think in December that was kind of looking at this issue as well, but specifically for agriculture.

Geoff Steendam:

So just an example of application. This is really for urban water supplies. So water supplies for towns and cities. One of the things that water corporations do is develop urban water strategies where they look at a range of different scenarios. And so that's where because there is this uncertainty of course about how much things might change into the future, they look at a range of different scenarios that capture that uncertainty and look at what supply might do versus what might demand do. And then at what point in time do they need to be thinking about augmentations or demand options or whatever it is. And so the guidelines are really a key tool for them to access and use the science and do that in a consistent way across the state.

Geoff Steendam:

So just in terms of next steps, so I mentioned the Synthesis Report, so that's being worked on at the moment. Expect to have that out later this year. At the same time we're reviewing and updating those guidelines with the latest science. And I guess in terms of looking to the future, if we're able to continue on with this kind of research, we are always trying to better tailor any research we do to better meet the needs of the sector. And we're also trying to leverage off all the other activities going on now just listed on the right, few other things that are happening around the country. And so we're always looking to sort of understand what's going on, how we can best fit and leverage off those other activities underway. And also help the water sector to navigate all of the data information that's available.

Geoff Steendam:

So that's the final slide there. So just a link to where you can go for some further information on the website. We do have a newsletter that we put out three or so times a year, so that's a good way to keep up to date with what's going on with the research program. In the bottom right there is the email address for the team. So HCS.Team@delwp.vic.gov.au, so if you'd like to be added to the newsletter just pop us an email and we can add you to the list. And look out for the Synthesis Report later on this year. So that's the end of the talk. Thanks very much. Hope everyone could hear that okay.

Alice Ritchie:

Certainly could hear it. Thank you very much Geoff. That was a fantastic and definitely thought provoking presentation. I particularly liked the application for the council's planning sort of into the future when they're going to start coming up with some pinch points. We've had a lot of interest. We've got 226 that have registered and 166 participants were online. And as I mentioned earlier, we will be sending this recording out to our climate webinars mailing list as well. So we might get a few more listens.

Alice Ritchie:

Myself and Heather, who's one of our other co-hosts will read out some questions to you. But just for participants feel free to keep putting questions into the chat box or if you want to use the hands up function we can unmute you. If you are asking your question via our hands up function, please provide your full name and what business or organization you're from. So I'll just start this off. We've got a quick one from Graeme Anderson. Thanks for the update Geoff, how does the measured catchment flow reductions post 1997 compare to what's in the climate change projections? Do you have any comments on that?

Geoff Steendam:

Yeah, that is a really interesting and challenging question I think that sort of gets to I guess we don't have a conclusive answer to that, but there is through the current program different research projects that are trying to help give some insights into answering that question. So since 1997 obviously we had the millennium drought sort of 13 years. And then since then still some declines in terms of courses and rainfall and then stream flows as well.

Geoff Steendam:

The projections for the future. Well the projections based on the global climate models we're really sitting on the bottom edge of those projections now. And there was a good image or graph of this in the Victorian Climate Science report that was released late last year. And so we're really tracking on the bottom edge of what we'd expect for declines now. So obviously there's climate change and climate variability in what we've seen. And the experience since 1997 will be a combination of both.

Geoff Steendam:

We are trying to better understand how much climate change is in that because many people in the water sector feel that, and I expect in the community too feel that the conditions since 1997 it's been 23 years, it's quite a long time to sort of be unlucky. But yeah, I guess the reality is it is a combination of climate change and variability, and we are trying to as much as we can get better figures on that through the program, but we'll never conclusively know or be able to fully quantify that.

Alice Ritchie:

No, that definitely ties in a little bit with Graeme had.... Around the 2019 new Victorian Climate change projections suggested that there might be bigger reductions in rainfall around the Alps, Victorian Alps than previously thought. So I suppose is still that issue around projections and how we're tracking relative to them.

Geoff Steendam:

Yeah, so I think yeah, it is challenging. There is a lot of projection information out there. And so I guess just trying to learn what we can from each of the different products is I guess where the focus lies. Yeah.

Alice Ritchie:

Yep. I've got one question about water quality from Andrew Lanchbury and then I'll throw it over to Heather who's got a few more questions waiting. So Andrew asked there's a long-term focus on quantity of water through stream gauging and rainfall measuring. In terms of watershed runoff quality, has this been integrated into hydrology work? So can this be used to analyse the changes in both quality and quantity, and what water availability is usable? So nutrients, salinity, solids, organics, algae, etc.

Geoff Steendam:

Yeah, so great question. Through this research program, it is very focused on quantity, but obviously that is a great question. I'm sure there is work around, but I'm just not really across it. So I'm probably not the best one to respond to that question.

Alice Ritchie:

Thank you very much for that Geoff. Heather, would you like to unmute yourself and ask some questions?

Heather:

Yes, Hi Geoff. I've got a few here that have come through to me. So I've got one from Cathy. Is there a relationship between development in the catchment, i.e. water harvesting in dams, and reduction in streamflow?

Geoff Steendam:

Yep. So what we're doing at the moment, so the University of Melbourne is looking at different variables or things across the catchment or with climate that could be potentially explain some of this shift in relationship that we've seen. And so things like development across the catchment is one of the variables that we're assessing to see and how much could that explain some of the changes that have been observed.

Geoff Steendam:

The catchments that I've selected here they're selected because they are catchments where there is relatively small amounts of diversions upstream. So these catchments are all upstream of any major storages or anything like that or any major diversions. But of course, across some landscapes still there's a lot of smaller I guess development including farm dams that potentially could have some impact.

Geoff Steendam:

So we are trying to understand, well how much could those changes influence what we're seeing here. I guess it is a relatively short timeframe though that this is being observed over. So some of the changes that might take decades to occur across the landscape. Because we're seeing this in quite short timeframes how much those things might explain what's been observed I guess we'll just have to wait and see when that analysis is done.

Heather:

Okay. Similar sort of questions so just let me know if you've covered everything, but from Brad. The research is great. Thank you. We'd love to see projections of population change in small towns due to climate change and Metro planning limits. What impact is considered along with reduced streamflow?

Geoff Steendam:

So I think that really gets to and maybe Heather or Brad, you might have to clarify here. But I think in terms of population change as a driver of demand, so I guess maybe that's where the question's going. So where water corporations supply water to towns, they look at not just a streamflow or sort of ground water availability or whatever water supplies they have. So they look on the supply side, but they're also looking on the demand side. So what are their demands and then how might those demands change into the future including as a result of population changes?

Geoff Steendam:

So I guess that those population changes for towns is considered in the work that they do. But I guess those changes aren't directly a part of the research that's going on here. So it's probably a question that's in most cases better directed to the water corporation in the local area. Unless you wanted to ask any further question on that.

Heather:

Okay. I'll see if Brad does come back with anything. But okay, so we'll move on. From Nick, could the greater fall in stream flow since the millennium drought be due to farming practices to increase water retention on farm and reduced runoff?

Geoff Steendam:

Yeah, I guess it's another possible change in the catchment that could be relevant. Again, I guess it's because a lot of these catchments are catchments where in some cases they're even fully forested catchments where there's no even no farming activities that occur, and we're still seeing this change in the relationship in those catchments too. So I think that shows that even though there's activities in farming areas that could potentially in fact impact this relationship to some degree. Because we're seeing it even in those catchments that are quite natural catchments, that's why sort of there's reason to think there's other things going on too. That's not to say that any particular activity won't itself have some impact either.

Heather:

Thanks Geoff. From James, could increased evaporation due to increase temperature account for reduced streamflow?

Geoff Steendam:

Yeah, so I mean, I think that increases in temperature obviously is something that is observed across all catchments and so natural catchments and cleared catchments. So that is one possibility for sure. And I guess when you think of a degree temperature rise, and one impact that could have on evaporation and transpiration. Yeah, it is certainly a possibility. Although there is quite a lot of debate amongst the scientists about even what temperature rises might do for evaporation and transpiration. So there's a lot of other things that can influence those things in addition to temperature. So it is still a fairly complex question and which is partly why it's so hard to nail exactly what's going on here.

Heather:

Okay. I've still got quite a number of questions coming in. So if we don't get to them all, we'll make sure that we document them and get them to people. From Nicholas, like the urban water projections, have supply and demand projects been done over whole river catchments.

Geoff Steendam:

Yeah, and I meant to mention, I may not have mentioned it, but sustainable water strategies is an example of ... So that's a legislated planning process that occurs in Victoria that looks across a region, and looks at supply and demand, environmental needs. And looks at also what's been observed in the past, but also what projections are for the future. To then understand that supply demand balance, if you like, from a much broader perspective to then inform policy and those processes work closely with communities to then have community input into the decisions that get made. So that's probably the best example to mention.

Heather:

Great, thank you. from Sally. She's wondering whether there is hydrology information that can be provided for specific catchments or gauging station sites. Recovered, non recovered for sites in the Ovens and King catchments.

Geoff Steendam:

So Ovens and-

Heather:

The King catchments in the Northeast. And she said maps are hard to interpret.

Geoff Steendam:

Yep. So the hydrology data set, the streamflow records so they are all publicly available on the water measurement information system. So W-M-I-S, WMIS that DELWP coordinates. Having said that there's still obviously there's quite a lot of sort of data analysis that sometimes has to occur to then sort of understand what exactly that means for your particular system. In terms of this kind of analysis, now I guess that's what we are and what Melbourne University are doing now and we will try and make it as available as we can.

Geoff Steendam:

So where there is local systems that people have an interest in, we can show the analysis that's been done in those systems, and what's going on locally. We're also looking at, because of the analysis it's done at stream gauging sites and for catchments above those sites, we are looking at ways to then understand what could be going on for those catchments where we can't easily do the analysis. So that's where those explanatory variables that got mentioned earlier, if we can better understand that potentially then we can sort of get some idea of what might be occurring elsewhere even if we don't have a streamflow gauge. So I think in terms of getting information for the Ovens and King, when we've got the analysis more complete later this year, then we can look to provide that information.

Heather:

Thanks Geoff, from Rob, do you notice a bigger reduction in runoff in catchments that have low rainfall compared to catchments with a high rainfall?

Geoff Steendam:

Yeah, so it does. There is when you look at some of those maps, there's really a strong kind of spatial signal. So even that map that showed the blue rain and red the blue being essentially the higher rainfall catchments in the great divide where we've seen no significant shift in the relationship, whereas in some of those other catchments that many of which are lower rainfall are where we're seeing a greater shift.

Geoff Steendam:

So I think the answer is when you look at those, it does appear that yes, that is the case. Which kind of gives some insights maybe into what's going on. But yeah, as I said, it's still kind of trying to work out what exactly that is. Because there's also a lot of other sort of variables that can change beyond just rainfall. But I guess, yeah, there's more often you're getting the more ephemeral catchments in those low rainfall areas.

Geoff Steendam:

And so when you are getting to that point where if you're not getting enough rainfall for a particular year, that you're even getting that surplus that can become runoff, then those catchments are more susceptible to sort of more sudden drop-offs in streamflow because they are much more on that more ephemeral end.

Heather:

Thanks Geoff. A question from Ralph. Ralph's wondering how the work that you were doing links in with the regional sustainable water strategies.

Geoff Steendam:

Yeah. And I mentioned here the sustainable water strategies. The work that we're doing here, and it's really there's the research and then the research updating the guidance. And so the guidance is used by water corporations to do their planning, but in the past, certainly the same guidance has informed how the sustainable water strategies assess water availability into the future. And even how they assess the risks to water availability today. So certainly there's been that consistency in the past. And so I would expect there's quite likely that all this research and the guidance would be a very strong input into the regional sustainable water strategies.

Heather:

Thanks Geoff. A question from Brad more on the past, does not represent the future statement in terms of population changes. If rural water corporations low predicted population changes, we see a very modest sometimes negative growth. What happens if we see bigger than expected population change? There is an impact on water resources and with the catchment health, and we model with regard to lower streamflows.

Geoff Steendam:

So I think maybe the first part of the question. So I guess there's, and really, so the water corporations are really the ones responsible for understanding their systems and understanding their customers and so they do look at uncertainties in demand, including the uncertainties in population changes into the future. And so even though population forecasts may be in some cases sort of zero or even potentially below that, water corporations often would be looking at, well, what if that's not quite right? What if there is growth? And then looking at an envelope around the population projections. But, sorry, what was the second part of the question?

Heather:

So the second part, what happens if we see bigger than expected population change?

Geoff Steendam:

Yep. So I think, yeah, that's again one of those sort of uncertainties that water planners have to manage and deal with. And so they do look at again, scenarios. So not unlike the scenarios on the supply side to deal with all the uncertainties we have around climate change and climate variability. But on the demand side too, yeah, we'll look at a range of scenarios because obviously there's uncertainties on the demand side as well.

Heather:

Thanks Geoff. We've been asked if we can share your PowerPoint and also the BOM hydro reference station websites. So if you're happy with that Geoff, we'll do that with all those who have registered. Question from Graham, what's typically the impact of bush fire affected areas on catchment runoff projections for the following decade or two?

Geoff Steendam:

I'm sorry, what was the last following decade or?

Heather:

For the following decade or two?

Geoff Steendam:

Yeah, so the bush fires, obviously there's bush fires have occurred at various different times in the past. And then I guess the hydrology and streamflow response that we see will reflect the history, bush fire history that's in that catchment. It's more there's certain tree species like Mountain Ash and Alpine Ash that I'm aware there's ... When you have a fire go through that's intense enough to actually kill the trees that's where you get that they regrow by seed. And so then you get a uniform, very dense regrowth occurring. And after sort of a number of years that regrowth because it is so dense, can actually use more water than the older ash trees that were there prior to the fire.

Geoff Steendam:

And so you can get a reduction in yield five to 10 years after a fire in those catchments. But in the initial years you actually get an increase because there's sort of less vegetation to start with post-fire. But then yeah, those types of tree species only exist in certain parts of the catchments, often in the high rainfall parts of the catchments. But because of the sort of mosaic of fire that you typically get, you do get in past fires at least there's been a lot of mixed species, which is a lot of the other types of the forest is the range of other tree species that tend to cope with fire much better and tend not to be killed by fire anywhere near as easily.

Geoff Steendam:

And even if they are the response can be different. So yeah, so I guess potentially there can be declines. But it very much depends on the tree species, the intensity of the fire and whether or not those trees are killed, and then what the vegetation response is like.

Heather:

Thanks Geoff, I think we've got a couple more questions and (inaudible) more minutes and we're still a hundred online, so we'll keep pushing through if that's okay with you.

Geoff Steendam:

Yep.

Heather:

From Megan. Are you doing this sort of research on ground water as well?

Geoff Steendam:

So groundwater is one of the things that's being considered in the analysis, so that hydrology analysis is looking at available groundwater records to understand how much what's changing with groundwater. So we can then understand, well, what's that mean then for surface water? So that is occurring as a part of that assessment of well, what's going on with those changes. But there is lots of other groundwater work and research that goes on. But, beyond the work that we do. So there's a lot that I wouldn't be across, but in terms of that particular issue, yeah, ground water is definitely being considered.

Heather:

Okay. From David just building on an earlier question, is it possible that rainfall may be coming more sporadic with longer and warmer drying times between events? Is this leading to catchments being less saturated more of the time and producing less runoff?

Geoff Steendam:

Yeah. so that could be a possibility. It's actually not one that we've been looking at with this particular research, but it's a really good I think suggestion for what we could be looking at. I guess one of the things that is being looked at is the change in seasonality of rainfall. And so that's being assessed as part of one of those potential variables that might partly explain what's going on with the change in the relationships. But yeah, what David has described there it's not being assessed quite in that detail, but it is a really good question.

Heather:

Thanks Geoff. Question from Michael. Given water security for users is under threat, will DELWP change water storage policy and look again at building or enhancing storages?

Geoff Steendam:

Building or enhancing what's the last word?

Heather:

Storages.

Geoff Steendam:

So yeah, that's beyond the research program. So that's not really something that I could cover here. So I guess yeah, those sort of decisions are not really for the research program but for other processes to take into account.

Heather:

One more question. Rosie who lives near Rocklands reservoir. It appears from the projections streamflows are going to keep reducing. Again, I'm not sure if you'll be able to answer this. She's wondering why CMAs are putting so much water down out of Glenelg River when there is ample water for regular rainfall that's saving the release for when there is a reduction.

Geoff Steendam:

Yeah. So that's maybe a bit of a... so I'm not across the specifics there so I couldn't really comment on that one.

Heather:

Sure. I think that's all the questions for me Alice.

Alice Ritchie:

Wonderful. Thank you very much for reading those out Heather. Look, I'd just like to say a massive thank you to Geoff. I think that was a really impressive comprehensive presentation and you can tell by the number of questions that we've got. So thank you very, very much. For everyone still listening, we do have another webinar coming up. It will be in roughly two weeks, we're just finalizing the date. We're going to hear from Cam Nicholson from Nicon Rural Services, on what influences decision-making in particular, outlining some approaches to help farmer decision making, including responding to seasonal risks.

Alice Ritchie:

So if you've subscribed to the climate webinar series, you will receive some information about this shortly, including an opportunity to register. And if you haven't yet subscribed to the climate webinar series, go to our website, agriculture.vic.gov.eu/climaterisk. We will stick it in some comments. That's it. Thank you very much everyone. We'll send the recording out when we get it processed. I will let everyone go. Heather, we can close the recording.

Geoff Steendam:

Excellent. Thanks everyone.

Alice Ritchie:

And Geoff-

Page last updated: 04 Oct 2021