Drying basin

The Australian    June 7 – 8, 2008  p.28
Dry future well ahead of schedule
      For the past decade, the autumn rains that heralded the grain planting season and produced winter pasture have failed in south-eastern Australia. This year was no exception: the last month was the driest May on record for Australia as a whole, while autumn 2008 was the eighth driest on record. For the Murray Darling Basin it was the fourth driest autumn on record, with a basin-wide average of just 40 mm of rain, well below the long term average of 128 mm. Autumn inflows into the Murray River were just 200 gigalitres or billion litres, the same as last autumn's record-setting low.  
    The head of the Murray-Darling Basin Commission, Wendy Craik, warns  "there is really no improvement in sight".

       Research by CSIRO scientists Wenju Cai and Tim Cowan has found that since 1950 Victoria has suffered a 40 per cent decline in autumn rainfall, compared with the long-term average. And that decline has been most severe in May. Cai says the decline "is not totally due to climate change, but it shows an imprint of climate change".
     Craik points to work undertaken by the Victorian Government, for its Northern Region Sustainable Water Strategy. It found that the inflows into northern Victorian rivers, including the Murray, have fallen over the past decade. In many they are now lower than the levels forecast under climate change by 2055.
     "We are there already," Craik observes. "We expected we might have to deal with that in 50 years time, but we didn't expect to have to deal with it right now, or that we had been dealing with it. The question arises, have we arrived and is this what the future is going to hold for the southern part of the basin, or is it going to get worse?"
    The Strategy report found that, over the last ten years, the rainfall over almost all of Victoria has been well below average. River flows have been even more severely reduced. The Campaspe River has been 69 per cent below average, the Broken River 48 per cent below, while the Goulburn and the Murray Rivers have both been 38 per cent below the long-term average.
    The long term average flow in the Murray is 6,595 GL. Under medium climate change in 2055 it is forecast to fall to 4,486 GL. But the continuation of the last ten years of low inflows would result in just 3,667 GL.  Victorian irrigators are accustomed to enjoying high levels of water security: under the long term average they got their full allocations 99 years out of 100. Under the climate change scenario that would drop to 85 years out of 100, but a continuation of the conditions of the past 10 years would reduce that further to 81 years out of 100. The results were even more severe on the Goulburn, Campaspe, Loddon and Broken Rivers.
     The irrigation season opens in July, and at this stage it looks like they will be zero.
Last July all Murray River irrigators had zero allocations, but they later rose to 43 per cent for Victorians, 32 per cent for South Australians, and 25 per cent in NSW.
    Craik says the current water planning and management systems have been "caught on the hop".  "We have had to put in place special arrangements to meet critical human demand last year and we have it place again this year. Nobody envisaged that we would have this sort of situation.  We thought these were things we could think about and deal with over time, but in fact we have had to deal with them right away."
     Something else has happened in the basin. Rainfall has been this low in the past, but river flows were never as low as they have been over the past decade. As Craik puts it: "average rainfall no longer results in average inflow".
      The Murray Darling Basin has a very dry catchment. Less than ten per cent of the rain that falls on it ends up in the rivers, compared with 39 per cent in Europe, 48 per cent in Asia and 52 per cent in Northern America. This makes the basin extraordinarily vulnerable to the impact of rising temperatures which increase evaporation.
    Wenju Cai has calculated that a one degree rise in temperature in the basin results in a 15 per cent reduction in river flow, or about 1850 GL less water in the river. The last three years in the basin were the warmest on record, with last year the warmest yet at 1.1ºC above average.
    The decline in autumn rainfall is critical to inflow because, as Cai explains, it wets the soil so that when the wettest time of the year arrives – winter and spring – the rain runs off the soaked soil and into the river.
    Research by Bertrand Timbal, conducted under the South Eastern Australian Climate Initiative, found that rainfall south of a line running roughly from Adelaide to Canberra began in declining in late autumn and winter in the 1990s. North of the line (known as the sub-tropical ridge) rainfall has declined in summer and autumn since 2000.  
     Timbal reported growing evidence that lower rainfall and reduced runoff in south-east Australia is linked to global warming.
     Craik says it is hard to believe it is not climate change at work. "The temperature effect, linked to climate change, the decline in autumn rainfall, again linked to global warming, so it is hard not to believe that climate change isn't a significant player in this drought."
    Hopes were high that last year's La Nina event would rescue the basin from drought.
    Head of the National Climate Centre, Michael Coughlan, said the last big La Nina event, in 1989, produced an autumn rainfall across the basin of 267mm. But this autumn it got just 40 mm. Coughlan points out the La Nina did at least bring good rainfall over the summer. "From November through January, summer rainfall, we had the sixth wettest four month period on record," he says. But that rainfall was not sufficient to wipe out the deficit of the last two years, let alone the last six dry years.
   Cai says there are two processes that affect May rainfall in south-eastern Australia:
the sea surface temperature in the Indonesian throughflow region in the western Pacific, which is part of the El Nino/La Nina cycle; and the subtropical Indian Ocean.
   Cai says there have not been many La Nina events over the past 30 years, "the system seem to be stuck in the quasi permanent El Nino phase".  Then last year, when one developed, it was essentially blocked by rising temperatures in the Indian Ocean.
    Barry Batters grows wheat, barley, oats, faba beans, chickpeas and lentils, in partnership with his wife Jenny, near St Arnaud in central Victoria. He describes his autumn 2008 rainfall as quite a bit below average, adding "it depends what average you are talking about. If you are talking about the last ten years average, it is about on par. But over the life-time of rainfall it is definitely below average."
    Batters says they no longer get the autumn break, or planting rain, they used to.
So farmers have adjusted by planting on whatever rain they get and conserving moisture. Instead of ripping out weeds and ploughing, which opens the ground and increases evaporation, they practise minimum till. That means spraying weeds with herbicides and planting the seeds directly into the soil. "Nowadays the opportunities [to plant] aren't as great as they used to be, you have to be quick. Everyone is looking at ways all the time to conserve the moisture when you sow," Batter says.
   Victorian dairyfarmer Stephen Mills is chair of Irrigation Australia, a director of Murray-Goulburn Cooperative, and was recently appointed to the Victorian Government's Future of Farming Advisory Panel. He readily admits the reduction in rainfall is making it harder for farmers to remain productive and viable. "But I still think there is a lot of hope for the way that farmers approach their production systems. We will see enormous changes in the next decade or so. We have seen changes already that perhaps we haven't recognised."
   Mills says dairy farmers are adopting new irrigation technologies "like sub-surface drip, and very fast flow surface flood irrigation, which are proving to provide very significant production increases, while maintaining very efficient water use". They are growing more lucerne, a deep-rooted crop that responds quickly to rainfall and needs less irrigation, and they have shifted their main irrigation season from spring to autumn.
   Mills says that, after deregulation in 2000, there were a lot of changes. He thinks changes will continue to occur, pointing out "there are enormous challenges".
   Milk prices are high, and the north Victorian milk supply "has really held up fairly well, with very low water allocations and low rainfall. That is a good sign that dairy-farmers are confident about the future, and are willing to change their practices."
    But across the Murray New South Wales dairy farmers have effectively had three years without a water allocation "and they are looking at zero again this year. Those farmers are really starting to struggle, their resilience has been hit hard. Those guys even at the milk price today are still questioning is there a future for them in that sort of rainfall scenario," Mills says.
     Chris Mitchell is the director of the Centre for Australian Weather and Climate Research, a partnership between CSIRO and the Bureau of Meteorology. He says the south-east rainfall decline is "a very active area of research. I don't think there is an answer that the scientific community has settled on".
     But he say there is no doubt that Australia has warmed as a result of global warming. "The extent to which that is affecting rainfall, compared to the natural variability that we have in our system, is really very, very hard to disentangle."
     Mitchell argues it is important to manage on the assumption  the downturn will continue. "If you are assuming that rainfall will return, you won't try and adapt to a drier climate and when you get hit by those dry years, it will impact your bottom line, you productivity and your system much more.  Whereas if it gets wetter, the chance is you will get a bumper crop, but the other years you will be OK."


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