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GCMs Validation Towards Realistic Impacts Assessment

GCMs Validation Towards Realistic Impacts Assessment. Data. Knowledge. Mpelasoka F., Bates B., Jones R. and Whetton P. | CSIRO Atmospheric Research. Creditability of GCMs. GCMs validation is hard and perhaps even a poorly defined problem

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GCMs Validation Towards Realistic Impacts Assessment

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  1. GCMs Validation Towards Realistic Impacts Assessment Data Knowledge Mpelasoka F., Bates B., Jones R. and Whetton P. • | CSIRO Atmospheric Research

  2. Creditability of GCMs GCMs validation is hard and perhaps even a poorly defined problem • Increasing confusions and uncertainties as models become complex (Rind, 1999; Petersen, 2000) • Inadequacy of traditional objective skill measures for diagnostics relevant to impacts assessment • | CSIRO Atmospheric Research

  3. Objectives To validate GCMs in terms of signals interpretable in the context of climate impacts • To examine time series structures for climate elements of interest • To evaluate covariance across spatial and temporal scales at which impacts occur • | CSIRO Atmospheric Research

  4. Strategy: Eigen-AnalysisBased Validation Singular Spectral Analysis (SSA) Scheme • Local assessment of time series structure Common Principal Components (CPCs) Model • Variability assessment of spatial and temporal eigenvalues • | CSIRO Atmospheric Research

  5. Basic SSA Scheme STEP 1 + STEP 2 :DECOMPOSITION STAGE STEP 3 + STEP 4:RECONSTRUCTION STAGE • | CSIRO Atmospheric Research

  6. CPCs Model Covariance matrices have different eigenvalues but identical eigenvectors (Flurry, 1984) • Implies multiple data sets share common components, but each set has different eigenvalues associated with those components • | CSIRO Atmospheric Research

  7. GCMs and Data GCMs:Mk3 (CSIRO, Australia) and HadCM3 (Hadley Centre, UK) • Mk3 horizontal resolution: 3.73 x 3.75 deg • HadCM3 horizontal resolution: 2.50 x 3.75 deg Data:Daily series of gridded simulated and observed variables for 1971-2000 • | CSIRO Atmospheric Research

  8. Test Site • Murray-Darling (M-D) Basin • Area = 1 060 000 km2 • Mean Precip = 508 000 GL/Yr • Runoff = 23 850 GL/Yr • Most precipitation is evaporated • | CSIRO Atmospheric Research

  9. Seasonal Distribution Observed Mk3 GCM M-D Basin: JJA 1971- 2000 Potential Evaporation • | CSIRO Atmospheric Research

  10. Seasonal Distribution Observed Mk3 GCM M-D Basin: JJA Precip 1971-2000 • | CSIRO Atmospheric Research

  11. Seasonal Distribution Observed HadCM3 GCM M-D Basin: JJA Precipitation 1971-2000 • | CSIRO Atmospheric Research

  12. Seasonal Distribution Observed HadCM3 GCM M-D Basin: DJF Tmax 1971-2000 • | CSIRO Atmospheric Research

  13. Local Assessment (SSA) Observed Mk3 GCM Bourke: JJA precip series structure (1971-2000) • | CSIRO Atmospheric Research

  14. Local Assessment: ‘Base’ Signal Observed Mk3 GCM Bourke: reconstructed JJA 1971-2000 precip ‘BASE’ signal • | CSIRO Atmospheric Research

  15. Local Assessment (Q-Q Plots) ‘BASE’ signals ‘PERTURBATIONS’ Bourke: Independent comparison of base and perturbations JJA precip signal distributions • | CSIRO Atmospheric Research

  16. Spatial Variability: Partial Eigenvalue Spectrum JJA precip variance DJF precip variance Partial eigenvalues of M-D Basin observed precip (95% confidence limits) versus partial eigenvalues of CSIRO Mk3 simulation • | CSIRO Atmospheric Research

  17. Concluding Remarks Averages-based validation • Tends to mask much needed detail relevant to realistic impact assessment (variability and extremes) • Different explanation might account for the same observations Eigen-analysis based validation • Considers structure and variability across a spectrum of spatial (global, regional, local) and temporal (inter-decadal, inter-annual, seasonal) scales • Pinpoints the causes of mismatches between observations and GCM outputs, leading to GCM improvement • | CSIRO Atmospheric Research

  18. Acknowledgements • Climate Impacts LINK Project, UK (HadCM3 data provision) • Janice Bathols and Harvey Davies - CSIRO, AR (NAP software application support) • Lorraine Bates and Geoff Hodgson - CSIRO, LW (GIS technical advisory support) • | CSIRO Atmospheric Research

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