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

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

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

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

Growth in storage capacity & diversions

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.

Scenarios used in modelling Historic climate ( ) & current development Recent climate ( ) & 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 AutumnSummer Winter Spring

Methods - overview

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

The pattern of water availability

Changes in seasonality

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

Relative level of use over 111 years

Climate change - Percent changes in runoff by 2030

Median climate change impact

Extreme climate change impact

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

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

Additional future surface water uses

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

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 Rainfall Runoff

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 More, longer and more severe dry runs Historic Climate change dry extreme

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

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

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

Murray-Darling Basin Sustainable Yields Project funded by National Water Commission