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

2. ACRE Workshop 2008 ●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 Acknowledgments

3. ACRE Workshop 2008 ●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 20 th Century? ●putting anthropogenic climate change in context ●stochastic assessments of system reliability Why ACRE & Water Resources?

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

5. ACRE Workshop 2008 Rules; What Rules? ●Traditional water planning based on assumption of stationarity (constant mean, variance & autocorrelation) ●Observed changes in 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?

6. ACRE Workshop 2008 ●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? Experimental Design

7. ACRE Workshop 2008 IWSS Inflows

8. ACRE Workshop 2008 Site Map

9. ACRE Workshop 2008 Nonhomogeneous Hidden Markov Model ●Observed process: sequence of regional precipitation occurrence patterns R t : t = 1, …, T ●Hidden discrete-valued process: sequence of weather types (or states) S t ●State to state transitions driven by atmospheric information (predictors) X t

10. ACRE Workshop 2008 ●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 ●DTd 850 = T 850 – Td 850 ●1 st canonical variate ●Testing: split sample & physical scrutiny NHMM Details

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

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

13. ACRE Workshop 2008 Synoptic Typing & Frequency Southwest Australia

14. ACRE Workshop 2008 ●Overall reduction in precipitation occurrence – changes most notable in west of the region ●Most sites exhibit reductions in mean wet-day precipitation amounts ●Some indication of increase in precipitation intensity in SW corner of the region At-Site Precipitation 1958 to 2007

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

16. ACRE Workshop 2008 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 20 th century putting anthropogenic climate change in context – if & when will the envelope of natural climate variability be breached (approximately)? Concluding Remarks

17. ACRE Workshop 2008 NHMM vs. Null Model OccurrenceAmounts PeriodSSMSSEErEr SSMSSEErEr 1958-7710306155670.39891975321987320.295 1978-927712100840.43368720816403540.295 1993-98319741870.4332802077277900.278

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

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