Climate Change Impact Assessment    for Sydney’s Water SupplyS. Maheswaran (Mahes), J. Martin and G. Kibria        Sydney ...
Study backgroundThis Study is a collaboration between•Commonwealth Scientific and Industrial Research Organisation (CSIRO)...
Sydney Catchment Authority•   Owns 21 storage dams and weirs•   Stores 2.6 million megalitres•   Covers 16 000 square kilo...
Greater Sydney’s Water Supply SystemMain Storages   • Warragamba   • Upper Nepean Dams (Avon,   Nepean, Cataract and   Cor...
Long term planning challenges •   Climate variability – Wet and dry cycles •   Population increase – Population to reach 5...
Historic rainfall and inflow variability  •   Water Supply system is exposed to high rainfall and inflow  variability  •  ...
GCM and Downscaling Method used •   Rainfall, Evaporation and Temperature data were downscaled to the     local/regional l...
Climate Scenarios  In this analyses, three scenarios were used - B1, A1B, A2 (Only A2 scenario presented here) Three time ...
Observed and Current Climate Rainfall DataDownscaled andobserved annualaverage rainfalldistribution isshown in the LHFigur...
Rainfall-Runoff ModelHSPF catchment models were calibrated using traditional techniqueswith an emphasis on ensuring that d...
Yield AssessmentYield is the maximum amount of water that can be extracted on asustainable basis from the water supply sys...
Scenario A2 : Annual Average RainfallDownscalingprocess was usedto generate 100rainfall andevaporation dailysequences forc...
A2 Scenario – Likely changes•Inland regions consisting of the majority of theWarragamba and Shoalhaven catchments tend tob...
Low persistence in future CC scenarios• Persistence is the relationship betweenrainfall and inflows in one year and those ...
ConclusionThe yield results were published in the NSW Office of Water Web Waterfor LifeClimate change impacts on water sup...
Findings• Bias in the annual level persistence in the downscaled rainfall isrecognized as a major issue in assessing clima...
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Ozwater 12 Presentation on Climate Change Impacts On Sydney S Water Supply

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  • HSPF catchment models were calibrated using traditional techniques with an emphasis on ensuring that dry periods are accurately represented. Calibration was undertaken to observed stream flow estimates of periods up to 20 years and then validated with a balance of up to 80 years.
  • This low persistence means that there are fewer significant droughts in the downscaled rainfall (Thyer et al., 2000) and inflows, resulting in a possible over-estimation of yield using the Wathnet model for water-supply allocation
  • Ozwater 12 Presentation on Climate Change Impacts On Sydney S Water Supply

    1. 1. Climate Change Impact Assessment for Sydney’s Water SupplyS. Maheswaran (Mahes), J. Martin and G. Kibria Sydney Catchment Authority 1
    2. 2. Study backgroundThis Study is a collaboration between•Commonwealth Scientific and Industrial Research Organisation (CSIRO)•Australian Government Department of Climate Change and Energy Efficiency•Office of Environment and Heritage (OEH)•NSW Office of Water (NOW)•Sydney Catchment Authority (SCA)•Sydney Water (SWC)•University of New South Wales (UNSW) 2
    3. 3. Sydney Catchment Authority• Owns 21 storage dams and weirs• Stores 2.6 million megalitres• Covers 16 000 square kilometres• Supplies bulk water for treatment and supply to 4.5 million people (60% of NSW)• Supplies raw water to 11 water filtration plants• Supplied 404 000 ML in 2011• 250 staff 3
    4. 4. Greater Sydney’s Water Supply SystemMain Storages • Warragamba • Upper Nepean Dams (Avon, Nepean, Cataract and Cordeaux) • Shoalhaven System (Wingecarribee, Fitzroy Falls and Tallowa Dam) • Blue Mountains dams, • Woronora Dam • Prospect DamDesalination Plant 250ML/dUpgradable to 500ML/d 4
    5. 5. Long term planning challenges • Climate variability – Wet and dry cycles • Population increase – Population to reach 5.7 Millions by 2036 • Water for environment –Environmental releases (80/20) commenced for Upper Nepean dams, Woronora dam and Tallowa dam and decisions of release regime from Warragamba Dam to be made in 2014. • Degree of success of water conservation, demand management and recycling projects • Climate Change Uncertainty 5
    6. 6. Historic rainfall and inflow variability • Water Supply system is exposed to high rainfall and inflow variability • Warragamba supplies almost 80% of the demand, estimated inflows and rainfall is shown below for last 120 years 6
    7. 7. GCM and Downscaling Method used • Rainfall, Evaporation and Temperature data were downscaled to the local/regional level using statistical techniques developed by UNSW • Outputs from CSIRO Mk3 GCM runs for three greenhouse gas emission scenarios—representing low, mid and high emission futures (B1, A1B, and A2 respectively) To better represent the uncertainty in possible climates, 100 replicates of rainfall and evaporation estimates were produced for the current climate and for each the future climate change scenarios in 2030 and 2070 The climate period for 1960–2002 is used as the baseline in this study as it is representative of the recent average climate in the Sydney region. It is referred to as the current climate 7
    8. 8. Climate Scenarios In this analyses, three scenarios were used - B1, A1B, A2 (Only A2 scenario presented here) Three time frames were used  Current climate between 1960 and 2003; and  Future climates 21-year period centred around 2030 (2020-2040) and 2070 (2060-2080) 8
    9. 9. Observed and Current Climate Rainfall DataDownscaled andobserved annualaverage rainfalldistribution isshown in the LHFigure.In general theaverage GCMdownscaled rainfalland evaporation area reasonablerepresentation ofthe current climate(RH Figure) 9
    10. 10. Rainfall-Runoff ModelHSPF catchment models were calibrated using traditional techniqueswith an emphasis on ensuring that dry periods are accuratelyrepresented. Calibration was undertaken to observed stream flowestimates of periods up to 20 years and then validated with a balance ofup to 80 years. Warragamba Annual inflows 8000 Obs 7000 HSPF 6000 5000 GL/a 4000 3000 2000 1000 0 1885 1905 1925 1945 1965 1985 2005 10
    11. 11. Yield AssessmentYield is the maximum amount of water that can be extracted on asustainable basis from the water supply system within the constraints ofthe design criteria – reliability, robustness & security.Design Criteria in SCA’s Operating LicenceSecurity: the SCA’s storages do not approach emptiness (defined as 5% of water in the storage) more often than 0.001% of the time.Reliability: restrictions last no longer than 3% of the time. That is, restrictions do not last for too long during any one drought event.Robustness: restrictions occur no more often than once in every ten years. That is, restrictions are not too frequent 11
    12. 12. Scenario A2 : Annual Average RainfallDownscalingprocess was usedto generate 100rainfall andevaporation dailysequences forclimate scenariosA2 for the 2030 and2070 assessmentperiods 12
    13. 13. A2 Scenario – Likely changes•Inland regions consisting of the majority of theWarragamba and Shoalhaven catchments tend tobecome drier with less average rainfall and moreevaporation•Coastal catchments slightly higher rainfall•The results showed that small reductions of averagerainfall and small increases in evaporation couldresult in disproportionate reductions to inflows. Thisis mostly due to concurrence of rainfall reduction andevaporation increase. 13
    14. 14. Low persistence in future CC scenarios• Persistence is the relationship betweenrainfall and inflows in one year and those inadjacent years.•This factor leads to long periods of droughtand is a key factor in the assessment ofsupply systems with many years of supplystorage capacity.•The persistence is statistically measuredas a correlation between each year’s flowand flows for previous years.•Figure shows the lag-1 coefficient of theWarragamba Current Climate and A22030 inflows•Key finding• GCM downscaled rainfall for the futureclimate and resultant inflows did not showany persistent droughts and lacked any lag-1 correlation on annual scales. 14
    15. 15. ConclusionThe yield results were published in the NSW Office of Water Web Waterfor LifeClimate change impacts on water supply were assessed based on aspecified water supply system configuration that represents a range ofgovernment policy decisions and planned infrastructureYield of the Greater Sydney Water Supply System•For A2 scenario, in 2030 the yield has been reduced down by around 8% and in 2070, yield is reduced by around 11%. 15
    16. 16. Findings• Bias in the annual level persistence in the downscaled rainfall isrecognized as a major issue in assessing climate change impacts onwater supply yield and is a key knowledge gap.• Further research required to investigate the issue of persistence in theGCM simulated variables and develop a methodology to correct theGCM variables so that rainfall obtained using these variables has theproper variability• SCA is partnering a study to address the shortcomings• The new study will  Improve statistical downscaling method  Incorporate Multiple GCM’s and RCM’s  Explore dynamic downscaling methods 16
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