South-West Western Australia Sustainable Yields Project Don McFarlane Project Leader
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 SWWASY Project – Water Corporation
Publications Main reports Executive summaries Factsheets Web: www.csiro.au/partnerships/SWSY.html CSIRO SWWASY Project – Water Corporation
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 SWWASY Project – Water Corporation
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 SWWASY Project – Water Corporation CSIRO South-West Western Australia Sustainable Yields Project – Overview
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 future climate (Cwet) • median future climate (Cmid) and • dry 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 not estimated to be important CSIRO SWWASY Project – Water Corporation
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 – Overview CSIRO SWWASY Project – Water Corporation
Annual rainfalls have been even drier since 1997 1997 to 2007 rainfall compared with 1975 to 1996 rainfall CSIRO SWWASY Project – Water Corporation CSIRO South-West Western Australia Sustainable Yields Project – Overview
14 of 15 GCMs project it will get drier Change in annual rainfall • Median future climate -7% • Wet extreme future -1% climate (90 percentile) • Dry extreme future -14% climate (10 percentile) Mid warming High warming Low warming CSIRO SWWASY Project – Water Corporation
Geographic scope • 13 surface water basins covering 39,000 km 2 CSIRO SWWASY Project – Water Corporation
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 SWWASY Project – Water Corporation
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 SWWASY Project – Water Corporation
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 SWWASY Project – Water Corporation
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 SWWASY Project – Water Corporation
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 SWWASY Project – Water Corporation
Groundwater results Geomorphic landforms affect groundwater response to climate change CSIRO SWWASY Project – Water Corporation
Groundwater models • The PRAMS model as used in the Gnangara Sustainability Strategy was Perth Regional Aquifer Modeling System used (PRAMS) • A new model for the Peel Harvey area was developed • The SWAMS model was Peel Harvey Regional linked to a recharge model Aquifer Modeling and recalibrated System (PHRAMS) • The Collie model was linked to a recharge model and Collie model South West Aquifer recalibrated Modeling System (SWAMS) CSIRO SWWASY Project – Water Corporation
Land cover likely to affect recharge / discharge Groundwater assessment areas • 56% dryland agriculture • 38% native vegetation • 6% plantations, urban, irrigated, open water CSIRO SWWASY Project – Water Corporation
Maximum depth of the watertable in the southern half of the Perth Basin in 2007 • Coloured areas are potential GDEs if not cleared • Coastal plain soils have very shallow watertables except Gnangara and Spearwood Dunes 22% • Plateaux areas mainly 14% 10% have deep watertables 46% CSIRO SWWASY Project – Water Corporation
Change in groundwater levels between 2008 and 2030 under climate and development scenarios CSIRO SWWASY Project – Water Corporation
Collie groundwater basin level changes between 2008 and 2030 Groundwater levels are less affected near rivers CSIRO SWWASY Project – Water Corporation
Level of confidence in the 2030 projections of groundwater levels • Central and Southern Perth Basin groundwater models are generally better than others • Northern Perth Basin and Albany Area require models • In some areas there is more confidence in specific aquifers. • Over a 22 year period the impact on deeper aquifers is present but muted CSIRO SWWASY Project – Water Corporation
Environment – key findings For surface water dependent ecosystems • Runoff during both the wet and dry seasons is expected to decrease by 20 to 30 percent under a median future climate • The impact of a drier climate is greater for low frequency- high flow events, but ecosystems are less sensitive to such conditions For groundwater dependent ecosystems • About 40% of potential GDEs may be affected to some degree under a median future climate • There are some localised high risk areas under the dry future climate and development scenarios CSIRO SWWASY Project – Water Corporation
Some terminology clarification • Runoff = amount of surface water flow expressed as a depth (mm) • Streamflow = amount of surface water flow expressed as a volume (runoff x area) • Surface water yield = streamflow that can be diverted for use. Takes account of water for the environment and the location of nature reserves, national parks, irrigable land, etc. • Use = water that is currently being used (metered, estimated) • Yield = the amount of surface water and groundwater that is available for use – either under license and as unlicensed ‘stock and domestic’ • Demand – as estimate of the future requirement for water as a result of economic, demographic and industry growth. Unmet demand may result in higher water prices, reuse, water conservation, trading, desalination, etc. as well as the curtailment of growth CSIRO SWWASY Project – Water Corporation
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