David Perovic (00:00): Hello everyone, my name is David Perovic,
and I'm a research officer with the Department of Primary Industries in [inaudible 00:00:06]
Today I'm going to give you a presentation on the longterm trends in cotton water productivity.
And this is one of four presentations from the water productivity benchmarking project
that were delivered at the Association of Australian Cotton Scientists Conference in
Armidale, 2019. This project is made possible thanks to the finding from the CRDC.
David Perovic (00:27): The objective of this work is to update the
longterm trends in cotton water productivity across the Australian cotton industry. These
longterm trends in water productivity were last updated in 2013, where they established
that the cotton industry married a 40% improvement in its water productivity over the then previous
10 years. So, we revisited this data from 2013 and then we added five years of new data
to update and reassess those longterm trends for water productivity across the whole industry.
David Perovic (01:11): So when we talk about water productivity,
it's the number of bales of cotton that make a [inaudible 00:01:18] and we can measure
the amount of water that we're interested in depends on the type of questions we're
asking about water productivity. So we might be interested in a question like, "How much
water does it take to grow cotton?" In which case we'd want to know all of the water that
the cotton crop uses, the irrigation water, rainfall, and any soil moisture that's been
stored in the field that the crop accesses. When we've got all of those pieces together
and we can measure what's called the gross product water use index, or GPWUI. What we
find is that at the scale that we're looking at here across the entire Australian industry,
the soil moisture component is not always available, so we have to rely on partial measure
for gross product water use, the GPW partial, which accounts for irrigation water and rainfall.
That is by far the most important components of overall water the crop uses. The soil moisture
component is a small component, but important.
David Perovic (02:38): So, looking at the trends in GPW partials
gives us a very good indication of what's happening in whole water usage. But what we
might be interested in is a slightly different question is, "How much irrigation water does
cotton use and how has that changed over time?" When we think about the water that's been
accessed from rivers and bores, how much of that is being used for cotton production?
As I said, how has that changed over time? When we look at just the irrigation water
we call that the irrigation water use index. So we're going to look at the response of
these three indices and the longterm trends of these three indices.
David Perovic (03:22): This data set that we put together is based
on industry data that goes back to the cotton season the Australian summer of 1987-1988.
All the data we've got we have information on water use, so we can calculate... irrigation
water, I mean. We can calculate irrigation water index for all of the data that we have.
But, there are only a handful of studies we were able to calculate the whole GPW, where
we've got the soil moisture component. For most of the studies we've got irrigation water
and rainfall, so we can get the partial GPW. What was also very interesting is that we
had independent data sets coming from the Australian Bureau of Statistics agricultural
water use that we could use to cross validate our data against.
David Perovic (04:37): I'll show you... get into the results. When
we look at the irrigation water, here's how productive irrigation water. We see that going
back to the late '80s there's been a very clear strong steady and statistically significant
improvement in water productivity over time. In fact, when we look back at water productivity
five years ago, water productivity in 2018 was significantly higher than it was in 2013.
When we compared the industry data for irrigation water use index, the ABS data, so it's an
independent cross validation, here we've got the industry data in the purple circles and
the ABS data in grey diamonds. You can see that number one, there's a very close agreement
in the two data sets, but most interestingly the trend in improved water productivity as
[inaudible 00:05:39] So that's a really nice validation of the data set.
David Perovic (05:51): When we look at the productivity of irrigation
plus rainfall, we see the same trend. We would expect this, but we see a steady statistically
significant improvement in water productivity going back to 1995 over the last two and a
half decades. When we have a look at the trend that we calculated for the data up to 2018,
we compare that to the rate of improvement we would have estimated with the data from
2013, we see that water productivity's actually increasing at a faster rate than we would
have thought that the data [inaudible 00:06:36] So not only is water productivity significantly
higher than it was in 2013, the rate of improvement we can see now is actually, it's increasing
at a faster rate than we would have estimated five years ago. That's because there was a
bit of a lull in water productivity for a couple of years as we came out of our drought.
David Perovic (07:03): Finally, when you look at the full profile
of water, we see the same trend as we did for the partial GPW, which is what we'd expect.
Again, a long, a strong, steady, statistically significant improvement of water productivity
over the past [inaudible 00:07:19] So this work that I've presented here is part of a
manuscript that we're putting together for peer reviews on the scientific journal paper
that hopefully will be coming out later on in the year and much more detailed on what
we did and the rate of change, the particular details can be found in that paper when it
comes out. This work has been part of a longterm project co-funded by CRDC and [inaudible 00:07:55]
called the Water Productivity Benchmarking Project that has looked at water productivity
across the cotton industry with the main objective of investigating whether the industry is using
water responsibly and efficiently. So that study goes back with a margin water productivity
for the last [inaudible 00:08:19] years. The longterm results will also feed into the CRDC
sustainability report 2019, which will also be coming out.
David Perovic (08:33): One thing that we have picked up from our
longterm water monitoring is that while we can see with a good idea of these longterm
trends that I've just outlined here, we still need to understand a bot more about the inter-seasonal
variation in water productivity or changes from one year to another and what are the
drivers in that. As we move forward we'll be benchmarking water productivity on an annual
basis as we go forward.
David Perovic (09:03): Finally, this work was down with a lot of
cooperation and collaboration and so big thanks go out to, first Guy Roth, University of Sydney
for sharing the data set that he put together when he updated the longterm trends in 2013.
Ali's a co-author in this study, as is Janelle Montgomery. Big thanks to Janelle and to Ali
Chaffey for the foundational work that they did on the benchmarking project, we're just
building on the great work that they've done in the past. Also, thanks to Jim Purcell,
Aquatech, for the WaterTrack software that he developed. It's been a big part of the
benchmarking project for the last 12 years. It's an important part of identifying the
data we collect and calculating the water balance that we used. Thanks to John Hornbuckle
who was a partner in the project at Deacon University, the IrriSAT technology also an
important part of our quality assurance data collection.
David Perovic (10:07): So, finally, if you're interested in the work
that we've presented here in terms of the longterm trends or if you're interested in
the benchmarking project, particularly if you're a grower or a consultant and want to
be involved in the benchmarking project, please contact Ben or myself on our DPI emails there.
Really interested to hear from you. Many thanks.