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Climate change and water resources in the Murray Darling Basin ...

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ABARE CONFERENCE PAPER 02.11<br />

efficiency <strong>in</strong> <strong>the</strong> <strong>Murray</strong> Darl<strong>in</strong>g Bas<strong>in</strong> rema<strong>in</strong>s largely unknown. Prior to <strong>the</strong> cap be<strong>in</strong>g<br />

placed on diversions <strong>in</strong> 1995, <strong>the</strong>re was little <strong>in</strong>centive for irrigators to <strong>in</strong>crease <strong>water</strong> use<br />

efficiency <strong>and</strong> hence <strong>the</strong>re is likely to be considerable room to adopt <strong>water</strong> sav<strong>in</strong>g technologies<br />

<strong>and</strong> practices <strong>in</strong> many areas. Hafi, Kemp <strong>and</strong> Alex<strong>and</strong>er (2001) reports that total<br />

system losses could be reduced by around 50 per cent with <strong>the</strong> refurbishment of channels,<br />

<strong>in</strong>creased use of drip irrigation <strong>and</strong> reuse systems <strong>in</strong> two irrigation areas <strong>in</strong> <strong>the</strong><br />

Murrumbidgee catchment. In <strong>the</strong> horticultural areas of South Australia, <strong>water</strong> use efficiency<br />

is relatively high, of <strong>the</strong> order of 75–80 per cent, because closed delivery systems are<br />

used. However, improved management techniques, such as <strong>the</strong> use of moisture probes to<br />

improve schedul<strong>in</strong>g <strong>and</strong> reduce irrigation depths, have <strong>the</strong> potential to substantially <strong>in</strong>crease<br />

<strong>water</strong> use efficiency on-farm (Anthony Meisner, Department of Environment, Heritage<br />

<strong>and</strong> Aborig<strong>in</strong>al Affairs, South Australia, personal communication, November 2000 <strong>and</strong><br />

April 2002).<br />

In <strong>the</strong> <strong>water</strong> use efficiency scenario, irrigation losses through ground <strong>water</strong> leakage,<br />

dra<strong>in</strong>age <strong>and</strong> overl<strong>and</strong> return flows were reduced by 50 per cent over <strong>the</strong> 100 year simulation.<br />

For example, <strong>in</strong> a region with a base level of <strong>water</strong> use efficiency of 60 per cent,<br />

an additional 20 per cent was phased <strong>in</strong> to <strong>in</strong>crease efficiency by 80 per cent by 2100. It is<br />

likely that improvements would occur <strong>in</strong> response to <strong>the</strong> decreased availability of <strong>water</strong><br />

for irrigation. Therefore, <strong>the</strong> rate at which efficiency ga<strong>in</strong>s were <strong>in</strong>troduced was scaled to<br />

match <strong>the</strong> rate of <strong>change</strong> <strong>in</strong> precipitation under <strong>the</strong> different global warm<strong>in</strong>g scenarios.<br />

The <strong>change</strong> <strong>in</strong> precipitation to 2100 was used as a base. For example, if precipitation falls<br />

by 3 per cent <strong>in</strong> 2050 <strong>and</strong> by 10 per cent <strong>in</strong> 2100, <strong>the</strong> reduction <strong>in</strong> irrigation losses <strong>in</strong> 2050<br />

would be 15 per cent; three-tenths of <strong>the</strong> maximum sav<strong>in</strong>gs of 50 per cent. The capital<br />

cost of undertak<strong>in</strong>g <strong>the</strong> efficiency improvements was not <strong>in</strong>cluded <strong>in</strong> <strong>the</strong> analysis.<br />

After <strong>in</strong>creas<strong>in</strong>g irrigation efficiency, less <strong>water</strong> is needed to ma<strong>in</strong>ta<strong>in</strong> <strong>the</strong> same level of<br />

crop production, lead<strong>in</strong>g to <strong>water</strong> sav<strong>in</strong>gs. Under <strong>the</strong> current property rights structure <strong>in</strong><br />

<strong>the</strong> <strong>Murray</strong> Darl<strong>in</strong>g Bas<strong>in</strong>, irrigators have <strong>the</strong> implicit right to reta<strong>in</strong> <strong>the</strong> <strong>water</strong> saved. In<br />

<strong>the</strong> simulations presented here, irrigators reta<strong>in</strong> <strong>the</strong>se sav<strong>in</strong>gs <strong>and</strong> use <strong>the</strong>m to exp<strong>and</strong> irrigated<br />

production. Alternatives not considered <strong>in</strong>clude leav<strong>in</strong>g <strong>the</strong> sav<strong>in</strong>gs <strong>in</strong> <strong>the</strong> river as a<br />

dilution flow or trad<strong>in</strong>g <strong>the</strong>m if an operational <strong>water</strong> market exists. The results of <strong>the</strong> <strong>water</strong><br />

use efficiency simulations are presented as <strong>change</strong>s <strong>in</strong> regional agricultural returns.<br />

Water trade scenario<br />

Water trad<strong>in</strong>g between irrigation areas has <strong>the</strong> potential to allow irrigators flexibility to<br />

adapt to climate <strong>change</strong> if <strong>water</strong> can be purchased to meet any shortfall <strong>in</strong> crop requirements.<br />

Even with appropriate property rights <strong>and</strong> <strong>in</strong>stitutional arrangements, <strong>the</strong> potential<br />

to trade <strong>water</strong> from outside <strong>the</strong> catchment does not exist <strong>in</strong> all regions. In <strong>the</strong> nor<strong>the</strong>rn<br />

catchments of <strong>the</strong> <strong>Murray</strong> Darl<strong>in</strong>g Bas<strong>in</strong>, irrigation takes place on tributary rivers <strong>and</strong> <strong>the</strong>re<br />

is little or no potential for <strong>water</strong> to be traded between catchments. However, <strong>in</strong> <strong>the</strong> south-<br />

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