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Water Resources: Hydroclimatic Forensics Through Reanalysis Climate Adaptation Bryson C. Bates Leader, Pathways to Adaptation Theme 24th June 2008 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 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 IWSS Dam Inflow Series Cost of system expansion: 2 billion AUD spent over last decade 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? ACRE Workshop 2008 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 10 1920 ACRE Workshop 2008 1960 Year 2000 0.2 0.02 1000 0.3 0.03 a 0.1 0.00 0.01 p-value Probability value 100 Inflow (Gl) IWSS Inflows b 6 2 8 6 hh 10 10 12 Site Map ACRE Workshop 2008 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 transitions driven by atmospheric information (predictors) Xt ACRE Workshop 2008 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 Interannual & Split Sample Validation Validation Fitting Simulated daily rainfall Fitting Fitting Validation Observed daily rainfall ACRE Workshop 2008 Dry spell Wet spell Validation Atmospheric Predictors (1983:2007) versus (1958:1982) ACRE Workshop 2008 Synoptic Typing & Frequency Southwest Australia Type 5: Dry Everywhere 0.4 Probability 0.2 1958 ACRE Workshop 2008 0 0.2 0 Probability 0.4 Type 3: Wet West & Central 1978 1998 1958 1978 1998 At-Site Precipitation 1958 to 2007 ● 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 ACRE Workshop 2008 SE Australia Total River Murray System Inflows (including Darling River) Modelled Annual Inflows - current conditions 30 000 Annual Inflow (GL) 25 000 20 000 Long-term Average Inflow (11 200 GL/yr) 15 000 10 000 5 400 GL/yr 5 000 6 300 GL/yr 4 150 GL/yr Average Inflows during Drought Periods 0 1892 1902 1912 1922 1932 1942 1952 1962 1972 1982 1992 2002 Drivers of Federation, WWII & current droughts? ACRE Workshop 2008 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 NHMM vs. Null Model Occurrence Amounts Period SSM SSE 1958-77 10306 15567 0.398 919753 2198732 0.295 1978-92 7712 10084 0.433 687208 1640354 0.295 1993-98 3197 4187 0.433 280207 727790 0.278 ACRE Workshop 2008 Er SSM SSE Er Indian Ocean Climate Initiative SW Australia Informed Adaptation 120 1925-1975 100 1976-2003 mm 80 60 40 20 0 Jan ACRE Workshop 2008 Feb Mar Apr May Jun Jul Month Aug Sep Oct Nov Dec SEACI Weather Type Probabilities: SE MDB "Dry Everywhere" ACRE Workshop 2008 "Wet Everywhere"