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Water Resources: Hydroclimatic Forensics Through Reanalysis

Water Resources: Hydroclimatic Forensics Through Reanalysis. Climate Adaptation. Bryson C. Bates Leader, Pathways to Adaptation Theme 24 th June 2008. Acknowledgments. Colleagues Steve Charles (CSIRO) Richard Chandler (University College London)

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Water Resources: Hydroclimatic Forensics Through Reanalysis

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  1. Water Resources: Hydroclimatic Forensics Through Reanalysis Climate Adaptation Bryson C. Bates Leader, Pathways to Adaptation Theme 24th June 2008

  2. Acknowledgments • Colleagues • Steve Charles (CSIRO) • Richard Chandler (University College London) • James Hughes (University of Washington) • Eddy Campbell (CSIRO) • Funding • Australian Climate Change Science Program • Indian Ocean Climate Initiative • South Eastern Australian Climate Initiative ACRE Workshop 2008

  3. Why ACRE & Water Resources? • The problem • characteristics of multi-year drought • short hydrologic record lengths < 100 years • reliability of water supply systems – over-rated &/or over-allocation? • ACRE applications • deriving the ‘recent’ envelope of natural climate variability • documenting atmospheric circulation changes that caused droughts prior to middle of 20th Century? • putting anthropogenic climate change in context • stochastic assessments of system reliability ACRE Workshop 2008

  4. IWSS Dam Inflow Series Cost of system expansion: 2 billion AUD spent over last decade ACRE Workshop 2008

  5. Rules; What Rules? • Traditional water planning based onassumption of stationarity(constant mean, variance & autocorrelation) • Observed changesin means, variance & extremes – old rules are breaking down • Trends or shifts:if, when & why? • Regimes(periods exhibiting stationarity)? • Use all of the record;or which part? ACRE Workshop 2008

  6. Experimental Design • Dam inflow series • trend? • change points & regimes? • Stochastic downscaling • changes in atmospheric circulation variables? • changes in frequencies of synoptic types? • At-site precipitation • changes in occurrence? • changes in amounts? ACRE Workshop 2008

  7. IWSS Inflows ACRE Workshop 2008

  8. Site Map ACRE Workshop 2008

  9. Nonhomogeneous Hidden Markov Model • Observed process:sequence of regional precipitation occurrence patterns Rt: t = 1, …, T • Hidden discrete-valued process:sequence of weather types (or states) St • State to state transitionsdriven by atmospheric information (predictors) Xt ACRE Workshop 2008

  10. NHMM Details • Season:May to October • Period of interest:1958 – 2007 • Fitting:sequential estimation – BIC • Number of weather states:6 • Atmospheric predictors: • mean MSLP • N-S MSLP gradient • DTd850 = T850 – Td850 • 1st canonical variate • Testing:split sample & physical scrutiny ACRE Workshop 2008

  11. Validation Fitting Fitting Validation Fitting Validation Dry spell Simulated daily rainfall Wet spell Observed daily rainfall Interannual & Split Sample Validation ACRE Workshop 2008

  12. Atmospheric Predictors (1983:2007) versus (1958:1982) ACRE Workshop 2008

  13. Synoptic Typing & Frequency Southwest Australia ACRE Workshop 2008

  14. At-Site Precipitation • Overallreductionin precipitation occurrence – changes most notable in west of the region • Most sites exhibitreductionsin mean wet-day precipitation amounts • Some indication ofincreasein precipitation intensity in SW corner of the region 1958 to 2007 ACRE Workshop 2008

  15. SE Australia Drivers of Federation, WWII & current droughts? ACRE Workshop 2008

  16. Concluding Remarks • Water planners confronting • historically-unprecedented drought • non-stationarity in dam inflow series • apparent increase in climatic risk due to anthropogenic climate change • ACRE can assist water planners by • providing additional information about envelope of natural climate variability – system reliability • providing explanations for the causes of major droughts prior to middle of 20th century • putting anthropogenic climate change in context – if & when will the envelope of natural climate variability be breached (approximately)? ACRE Workshop 2008

  17. NHMM vs. Null Model ACRE Workshop 2008

  18. Informed Adaptation Indian Ocean Climate Initiative SW Australia ACRE Workshop 2008

  19. "Dry Everywhere" "Wet Everywhere" SEACI Weather Type Probabilities: SE MDB ACRE Workshop 2008

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