Water availability, drought and climate change in the MDB: a hydrological perspective

1. Water availability, drought and climate change in the MDB: a hydrological perspective Mac Kirby MDB Water Policy Workshop, Brisbane 21 October 2010

2. Outline • The Murray-Darling Basin Sustainable Yields project • Results • A closer look at drought • Implications

3. The Murray Darling Basin (MDB) • 1,000,000 km2 • 1/7 of Australia • 80% of basin is agriculture • 60% of Australia’s irrigation • “Food Bowl” of Australia • Population 2,000,000 • 6 jurisdictions

4. Rainfall varies considerably from east to west 2400 mm in SE < 200 mm in west Rainfall and runoff characteristics • Most runoff from small area • Only rivers in south are reliable

5. Growth in storage capacity & diversions

6. Murray-Darling Basin Sustainable Yields Project • Water Summit: Prime Minister and First Ministers, Nov 2006 • CSIRO to report progressively on sustainable yields of surface and groundwater systems within the MDB • Estimate current and likely future (~2030) water availability in each catchment/aquifer and for the entire MDB considering: • climate change and other risks • surface-groundwater interactions • Compare the estimated current and future water availability to that required to meet the current levels of extractive use • Results reported for 18 regions and entire MDB through factsheets, summary brochures and technical reports.

7. Scenarios used in modelling Historic climate (1895-2006) & current development Recent climate (1997-2006) & current development Future climate & current development 2030 climate based on 4AR IPCC results 3 global warming levels (low, mid, high) 15 global climate models We choose a high extreme, median and low extreme for reporting Future climate & future development Future development Commercial forestry plantations Farm dams Groundwater extractions Autumn Summer Spring Winter

8. Methods - overview

9. Surface and groundwater models used in the 18 MDB reporting regions Warrego IQQM Nebine IQQM Paroo IQQM Lower Balonne IQQM St George SGCS13NT Barwon-Darling IQQM Middle Condamine IQQM Condamine MODFLOW Menindee IQQM Upper Condamine IQQM Bidgee IQQM Border Rivers MODFLOW Lower Bidgee MODFLOW Mac. b and Bor. RivIQQM Moonie IQQM Murray BigMod Lower Gwydir MODFLOW Murray MSM Gwydir IQQM Upper Namoi MODFLOW Eastern Mt Lofty Ranges 6*WATERCRESS Peel IQQM Namoi IQQM Lower Namoi MODFLOW Macq-Castlereagh 6*IQQM Southern Riverine Plains MODFLOW Macquarie MODFLOW Lachlan IQQM Wimmera REALM Mid-Lachlan MODFLOW Lower Lachlan MODFLOW Avoca REALM Daily Snowy SIM_V9 Weekly ACTEW REALM GSM REALM Monthly Ovens REALM Mid Bidgee MODFLOW Upper Bidgee IQQM

10. The pattern of water availability

11. Changes in seasonality

12. Relative level of surface water use MDB: about half of available surface water is diverted for use ~11,300 GL/year on average; from ~23,400 GL/year

13. Relative level of use over 111 years

14. Climate change - Percent changes in runoff by 2030

15. Median climate change impact

16. Extreme climate change impact

17. Impact of climate change on availability MDB: median impact is an 11 percent reduction in available water ~2500 GL/year on average

18. Change in volumes diverted for use MDB: 4 percent reduction in total diversions ~450 GL/year, with current sharing rules

19. Additional future surface water uses

20. A land of droughts…. • Droughts about every ten years • Associated with El Nino • Also long term cycles

21. Current drought in detail - runoff • Not proven to be climate change • Runoff dramatically down (especially 2006/7) • Temperature increase • Reduced autumn rain, reduced autumn and winter runoff Runoff Rainfall

22. SY project drought projections - eg runoff in Condamine • Reflects general pattern of drought in the MDB • Climate change dry extreme projection drier than historic • Projection uses scaled historic, hence similar pattern • Long dry runs with reference to historic median Climate change dry extreme Historic More, longer and more severe dry runs

23. Runoff long dry runs • Climate change projections show more, longer and more severe dry runs • Impacts greater in south • Dry extreme and median projections show great impacts • Wet extreme similar to historical

24. Key messages Large proportion of surface water used for irrigation Large year to year variation - short and long term Large uncertainty in climate change projections - use as planning scenarios Despite the uncertainty all scenarios say the southern basin will get drier MDB median climate change impact is: 11 percent reduction in available water (2,500 GL/year) 4 percent reductions in water use (450 GL/year) Impact of climate change expected to be considerably greater than ‘other risks’ BUT high uncertainty associated with climate impacts

25. Drought implications • Recent drought in some ways different to past droughts - the past may not be a reliable guide to the future • Need to consider scenarios outside the range of past experience, including climate change scenarios • In recent drought there was insufficient water for either environment or irrigation. Current expectations could not be met. Extremely challenging, may be more so in future • No easy fixes (more large dams irrelevant, for example) • Improving irrigation (hydrological) efficiency may help, but • Amounts to be saved may be modest • Need to account for return flows • Not lowest cost

26. www.csiro.au/partnerships/SYP.html Murray-Darling Basin Sustainable Yields Project funded by National Water Commission