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Australia's Murray Darling Basin is going downhill

Written 2007/04/21, modified 2015/10/21
Contact: email daveclarkecb@yahoo.com
Also see South Australia's water supply

Introduction

Due to anthropogenic climate change, Australia's Murray Darling Basin, where a large part of the country's agricultural produce was once produced, is in a state of decline that will continue.

Australians are the worst greenhouse polluters on the planet - with the possible exception of a couple of small oil-rich Middle Eastern states - and are having to pay a high price for their practices

Murray-Darling Basin
Map of the Murray-Darling Basin, south-eastern Australia

On this page...

Drought
Increasing temperatures
Decreasing rainfall trend
Less run-off due to CO2
Less run-off due to fires
Research on likely declines in Murray-Darling
Conclusion
A summer rainfall event
Links
Index

Other pages...

The real cost of water
Water in South Australia
Neither of the big political parties will do much about greenhouse/climate change, vote smart.
 
About 40% of Australia's agricultural produce has come out of the Murray-Darling Basin in the past.

The aim of this page is to make another small attempt to force the Australian people out of their apathy regarding greenhouse/climate change. We must quickly start to change our life-styles and make substantial steps toward sustainability.

Australian governments and the Australian people have done very little to act on greenhouse pollution, so there seems to be a crude justice in this looming disaster. If there was a god, you would have to conclude that he was punishing Australians for their arrogance and for damaging his creation.

Ironically, both the current PM, Kevin Rudd, and the previous PM, John Howard, are believers; yet both support the coal industry at the expense of the health of 'God's creation'. Both are against sufficient and sufficiently prompt action against climate change. The loss of the irrigation industries in the Murray-Darling basin will cost the country hugely. Kevin Rudd and others who are slow to tackle the causes of climate change seem to forget that if renewable energy replaced coal, jobs and wealth generated by the renewable energy industry would tend to replace those lost in the coal industry.




Drought

The south-eastern part of Australia is currently (late 2008) in a drought that has lasted more than seven years. This has greatly exacerbated an already deteriorating situation. It has brought the decline in the health of the Murray-Darling Basin to a head earlier than would have happened otherwise.

Research into the climate of the last 30 years jointly by the Bureau of Meteorology and CSIRO (released Sept. 2007) has indicated that the drought is more likely due to a permanent change to the Walker circulation than just to a slow change from the drought producing El Nino back to the rain producing La Nina. Read about it on the ABC. The report indicates that annual rainfall in the Murray-Darling Basin is likely to decline by from 2-5% by 2030. Significantly, most of this decline will be in winter and spring.

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Increasing temperatures

Mean temperatures, Murray Darling Basin
Mean temperatures in Australia's Murray-Darling Basin
Temperature has been increasing, especially since about 1950
The graph on the right shows that mean temperatures have been rising for a number of years; it appears that the rate of rise is also increasing. As temperatures rise the water needs of plants increase and evaporation rates increase, so less water flows down streams into storages and less water is available for irrigators while the plants they grow need more water due to the higher temperatures.

Temperatures in the Murray-Darling Basin will continue to rise and runoff will continue to decline. Of course there will be some good years to come, but in general the trend will be down.




Rainfall has decreased

Rainfall trend, Murray Darling Basin
Rainfall trend 1970-2006 in eastern Australia (mm/10yrs)
From the Bureau of Meteorology
The map at the right shows that the rainfall trend over the past 36 years in the Murray Darling basin is toward a serious decline.

The colours indicate trends in millimetres of rain per ten years. That is, the darkest brown colour shows places where there has been a decline of at least 50mm in the ten-years rainfall. (I find this way of stating the trend a bit difficult to understand, but it seems to equate to a decline in average annual rainfall of at least 5mm each year for the 36 years. It is easy to see that this is a huge decline in rainfall, totalling a reduction of 180mm in average annual rainfall over the period.)

From the map, the Murray Darling basin in general is not suffering quite such a decline in rainfall as is Gippsland and the NSW SE coast, but there is a decline of between 20 and 30mm/10yrs over a very large part of the basin. Perhaps more importantly, the trend is between 30 and 40mm/10yrs over some of what has been the best-watered part of the basin.
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Decreased run-off due to higher carbon dioxide levels

Research done by Anna Ukkola and Albert Van Dijk reported on The Conversation on 2015/10/21 links higher atmospheric carbon dioxide levels with reduced run-off in "subhumid and semi-arid" part of Australia. The map included in The Conversation article indicated that the wetter parts of the Murray-Darling Basin are all within these zones.





Decreased run-off due to more frequent burning

Research has been done, I think by the CSIRO, indicating that forest that has been burned in the last few years takes up a larger percentage of the rainfall than mature forest, leaving less to run off. It seems that recovering forest has a greater need for water than mature forest. It therefore is more effective at using the available rainfall for its own needs rather than allowing that rainfall to run off.

Other research indicates that bushfires will in future be more frequent in the headwaters of the Murray Darling due to the higher temperatures.






Research on likely decline in flows in Murray-Darling

In September 2003 Earth Tech Engineering produced a report titled "Preliminary review of selected factors that may change future flow patterns in the River Murray" for the Murray-Darling Commission. The report looked at a number of factors that were likely to produce changes.

Climate change (research done by Francis Chiew, University of Melbourne) was seen as likely to reduce flow by 5% (1100GL per annum) in the next 20 years, with the possibility (worst foreseeable) of causing a reduction of 20% (4400GL per annum) in the same period. (I find it unlikely that the decline will be as small as 5%, I will continue researching the matter, and would welcome information on the subject from readers. Perhaps global dimming has been a significant factor and will continue to be?) In 50 years Chew suggested a likely 15% (3300GL per annum) reduction and possible 50% (11 000GL per annum) reduction in stream flow due to climate change.

The likely impact of reforestation was researched by Lu Zhang of CSIRO/CRCCH (Commonwealth Scientific and Industrial Research Organisation/Cooperative Research Centre for Catchment Hydrology) for the same report. The likely 20 year impact was seen as a 600GL reduction in annual flow with a possible reduction of 1400GL. The likely 50 year impact was seen as a 1100GL reduction with the worst foreseeable reduction being 2100GL in annual flow.

Other factors such as increased groundwater extraction, changes in drainage and returned flows, and construction of farm dams were also expected to cause significant reductions in future flows.

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Conclusion

There are then at least four different factors that will all lead to decreased future flow in the Murray Darling river system:
  1. Increasing temperatures,
  2. Decreasing rainfalls,
  3. Less run-off due to fires,
  4. and less runoff due to reforestation in the Basin.
To say that the outlook for the Murray-Darling Basin looks grim would be an understatement.

The first three of the above factors are related to greenhouse/climate change. Australia, government and people, must do more. There has been a lot of talk; it is past time for the talk to stop and the action to get serious.






A summer rainfall event

Rainfall, week ending 2008/12/14
Rainfall in the week ending 14th Dec. 2008
Bureau of Meteorology
(While the map is the total rainfall for the week ending 2008/12/14, most of the falls in the SE corner were in the 72 hours to 9am on the 14th.)

Rain of 12-14th Dec. 2008

Calculating approximately from the BoM rainfall map on the right indicates that the Murray-Darling Basin received about 27TL (27 teralitres = 27 000GL) of rainfall.

Putting this in perspective:

The Murray Darling Commission Net site states that the area of the basin is 1 061 000km2; I have taken the average rainfall over the basin as being 25mm (from the map above). Hence 1 610 000 x 1 000 000 x 0.25 = 27 000 000 000m3 = (approx.) 27TL.

How much of the 27TL will go into the reservoirs or flow down the Murray? I'd be surprised if it was as much as 1%. By far the greatest part will be absorbed by the very dry soil and will either transpire or evaporate over the next few months. Where I live, Crystal Brook, there was 76mm of rain; there was runoff from the town area, but none from broad acres; the Brook did not flow. There would be runoff from areas with exposed rock or shallow stoney soils, but the Crystal Brook experience (there are some area of shallow, stoney soils upstream of the town) suggests that even these will not produce much flow.

Summer rainfalls, while they do great good for the remnant native vegetation, are all but useless so far as the flow and storages in the Murray-Darling basin is concerned.
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Links

There is an interesting article on Irrigation in the Murray Darling Basin on the Murray Darling Basin Commission's site. Table four on this page gives gross margins per megalitre for the main crop types grown in the Murray Darling Basin.





Index

On this page...
Conclusion
Decreasing rainfall trend
Drought
Increasing temperatures
Introduction
Less run-off due to fires
Decreased run-off due to higher carbon dioxide levels
A summer rainfall event
Links
Reforestation
Research on likely declines in Murray-Darling
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