South-West Western Australia Sustainable Yields Project Don McFarlane Project Leader
Acknowledgements • DEWHA – funding and policy guidance • Department of Water – data, models, researchers, report review • Water Corporation – data, report review • Department of Agriculture and Food WA – soils data • Bureau of Meteorology – climate data, surface water modelling • Queensland Department of Environment and Resource Management – SILO data • Contracts and consultancies • URS – Peel Harvey groundwater model • CyMod Systems Pty Ltd – groundwater model calibration • Resource Economics Unit – demand estimation • Geographic Information Analysis – model data preparation • Jim Davies and Associates – yield and demand analyses • External reviewers: Peter Davies (University of Tasmania); Andy Pitman (University of New South Wales); Tony Jakeman (Australian National University): Don Armstrong (Lisdon Associates) and Murray Peel (University of Melbourne) CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Broad terms of reference • Estimate the current and 2030 yield of water in catchments and aquifers for the south-west of WA considering climate change and development (plantations, farm dams, groundwater abstraction) • Compare the estimated current and future water yields to those needed to meet the current levels of extractive use, future demands and environmental needs CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Publications Main reports Executive summaries Factsheets Web: www.csiro.au/partnerships/SWSY.html USB Sticks CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Project context Environmental impacts of This Project alternate allocation regimes Water resource Assessments Socio-economic impacts of planning, of current and alternate allocation regimes management future water and yields and investment demands Stakeholder and community consultation • The project does not determine sustainable yields or set new allocation limits • The project is regional and doesn’t address local issues • The results are scenarios based on assumptions about the future climate, landuses, abstraction levels and demands CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Sustainable Yields Projects – 2007 to 2009 Murray-Darling Basin Northern Australia South-West Western Australia Tasmania CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Location of the project area • All fresh, marginal and brackish surface water catchments between Gingin Brook and the Hay River • All aquifers within the Perth and Collie basins, plus the western Bremer Basin • Area = 62,500 km 2 CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Project area topography • Short streams that arise in the Darling Ranges are fresh • Darling Fault separates Perth Basin from Darling Plateau • Coastal plains are flat and low lying – Swan Coastal Plain; Scott Costal Plain; South Coast • Perth Basin Plateaux are higher in elevation CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Land cover • Surface water catchments are mainly forested • About 60% of the Perth Basin is cleared about 56% of this being under dryland agriculture Gnangara • The uncleared areas Mound include coastal areas north of Perth, the Gnangara Mound and the Blackwood Plateau Blackwood Plateau CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Climate – 1975 to 2007 Potential Rainfall - APET evapotranspiration CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
South-west WA has had reduced rainfall since 1975 May – July August October – 600 500 -18% Total rainfall (mm) 400 300 200 -8% 100 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 The 1975 to 2007 period is the baseline for all subsequent comparisons CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Scenarios • The ‘historical climate’ or Scenario A assumed that the climate of the last 33 years (1975 to 2007) would continue. This was used as a base case for comparison of other climate scenarios • The ‘recent climate’ or Scenario B assumed that the climate of the last 11 years (1997 to 2007) would continue. • The ‘future climate’ or Scenario C used 15 GCMs with 3 GHG emission levels which would result in 0.7, 1.0 and 1.3 o C of warming by 2030 = 45 possible climates. They are reported as • wet extreme future climate (Cwet) • median future climate (Cmid) and • dry extreme future climate (Cdry) • Current levels of abstraction and land use were assumed to continue for all scenarios above • The ‘future climate and development’ or Scenario D assumed a median future climate and full groundwater abstraction, new plantations and farm dams (where important) CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
14 of 15 GCMs predict it will get drier Change in annual rainfall • Median future -7% climate • Wet extreme future -1% climate (90 percentile) • Dry extreme future -14% climate (10 percentile) Mid warming High warming Low warming CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Geographic scope • 13 surface water basins covering 39,000 km 2 CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Rainfall runoff modelling • Runoff simulated using five simple conceptual models • Sacramento • IHACRES • SIMHYD • AWBM • SMARG • One catchment model • LUCICAT (in about half the catchments) • The calibrated model output was compared with observed data and an average of runoff from Sacramento and IHACRES was the best CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Catchment representation Collie Basin • 0.05 o x 0.05 o grid (~ 5 x 5 km) • Each cell mapped into a catchment • Flow accumulated for 204 defined streamflow reporting nodes CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Calibration results – examples 500 500 Harvey River - Dingo Road Observed NSE = 0.82 Annual runoff (mm) . Modelled annual runoff (mm) 400 400 Modelled 300 300 200 200 100 100 0 0 400 400 Scott River - Brennan's Ford NSE = 0.87 Observed Annual runoff (mm) . Modelled annual runoff (mm) Modelled 300 300 200 200 100 100 0 0 0 100 200 300 400 1975 1985 1995 2005 Observed annual runoff (mm) Average model efficiency = 0.84, >0.8 in 80% of catchments CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Averaged across the surface water basins 15 global climate models project less runoff inmcm ncar_pcm Runoff change across all basins iap Wet future climate -10% cccma_t63 Global climate models ipsl Median future climate -25% miroc cnrm Dry future climate -42% cccma_t47 ncar_ccsm mri mpi gfdl csiro Mid warming giss_aom miub -50 -40 -30 -20 -10 0 High warming Low warming Change in runoff from historical (%) CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Rainfall, runoff and runoff coefficient under historical climate CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Projected change in mean annual rainfall relative to the historical climate • Rainfall declines by 8% under median future climate and 14% under dry climate • Proportion of area receiving over 900 mm is: 37% under historical climate, 34% under recent and wet future, 22% under median future, and 16% under dry future climate CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Projected change in mean annual runoff relative to the historical climate • Runoff declines by 25% under median future climate and 42% under dry climate • Proportion of area generating 110 mm runoff is: 37% under historical climate, 34% under recent and wet future, 22% under median future, and 16% under dry future climate CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Projected changes in rainfall and runoff Percent change Historical relative to historical climate Surface water mm Recent Wet Median Dry modelling area Mean annual rainfall 837 -2% -2% -8% -14% Mean annual runoff 98 -7% -10% -25% -42% Frequency of rainfall exceeding 900 mm 1 in 5 1 in 9 1 in 8 1 in 14 <1 in 33 generating more than years years years years years 130 mm runoff CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
Percent decline in runoff in all basins Northern region Central region Southern region d t o s o a w l o a k C t s c a n a k o o l y n B r n C t l o y a y l n l o e e e n n r m a e e n e t n v s n Change in mean annual runoff (%) i r s r t g w n a r i s n n r r a l e u n a l o a e w u e o o h r M W i H D D P B K G S C L S 0 -10 -20 Recent climate -30 Median future climate -40 • Decline under recent climate is greatest Gingin to Collie • Decline under median future climate more uniform across the area CSIRO South-West Western Australia Sustainable Yields Project – Bunbury
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