climate change, extreme sea levels & hydrodynamical models
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Climate change, extreme sea levels & hydrodynamical models
Introduction
Quantifying the impacts of climate change upon extreme sea levels.
Spatial variation in impacts. Scientific tools -
• Observational data, • Process knowledge,• Numerical models
Statistical tools • Extreme value theory, • Spatial statistics, • Nonparametric regression • Multivariate analysis
Hydrodynamical models
North Sea models
< 35km NEAC grid <
12km NISE grid V V
Scientific problems
Observational climate data Observational climate data for 1970-1999. Model output verified against observational sea level data. Test for evidence for temporal change in extreme values.
Numerical climate model Generate 30-year long stationary sequences of sea level
data. Climate input data generated using ECHAM-4 climate model
under two scenarios: current CO2, double current CO2. Interest is in comparing extremal characteristics of the
spatio-temporal fields generated under the two scenarios.
Previous findings
Surge residuals Annual maxima Univariate extreme
value modelling for each site
Use the GEV (Generalized Extreme Value) distribution
Changes in 50 year surge residuals (in cm) as
a result of a doubling of CO2 levels
/1
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xxF
Statistical methods for spatial extremes
An example Spatial variability Spatial coherence Residual spatial dependence
Insert a map here: simulated parameter
surface
Initial location = 0, Scale = 1, Shape = -0.35,Dependence = 0.7
Methods
Insert a diagram here
Multivariate extremesGeneral theory Componentwise maxima Multivariate extreme value distribution Modelling of marginal and dependence
characteristics Parameter linking
Inference 2-step likelihood estimation
• Independence working assumption• Sandwich variance estimator• Fix margins, transform and estimate
1-step likelihood estimation.
/1/1exp),( yxyxF
BEVL (Bivariate Extreme Value Logistic)
distribution
A local grid-based method
GridEvaluation
points
Kernels
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Acknowledgements
Supervisors Janet Heffernan Jonathan Tawn
Assistance and advice Johan Segers, Vadim Kuzmin, Alexandra Ramos, Christopher Ferro, Alec Stephenson, Matthew Killeya
Images Web sources (list available on request)
Lamb, H. (1991) Historic storms of the North Sea, British Isles and Northwest Europe, CUP, Cambridge.
Apparent independence
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