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Dilumie Abeysirigunawardena

Climate Impact Researcher BC Ministry of Environment

Ph.D. Candidate University of Victoria

dilumie@uvic.ca

or

Dilumie.Abeysirigunawardena@gov.bc.ca

Extreme Storm Surge and Wind-storm Climatology in the South coast of British Columbia

RESULTS SUMMARY

CIG Seminar Series, 29th May 2008, University of Washington, USA

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The Objective

Study the response of Extreme Sea levels and Windstorms to Natural Climate Variability

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Data

(1) Pacific Region tide gauge stations

Total Water level data (TWL) = Tide + Residuals

List of Tide Gauge Stations

(1) 7120-Victoria Harbour

(2) 7277- Patricia Bay

(3) 7735-Vancouver

(4) 7795-Point Atkinson

(5) 8074-Campbell River

(6) 8408-Port Hardy

(7) 8545-Bamfield

(8) 8615-Tofino

(9) 8735-Winter Harbour

(10) 8976-Bella Bella

(11) 9354-Prince Rupert

(12) 9850-Queen Charlotte City

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Data

A typical Tidal constituent table & Residual Time-series

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Directional Wind Data:

YVR - (1953-2006) (53-

Years)

Sandhead - (1993-2006) (14-Years)

Saturna - (1993-2006) (14-Years)

Data.

Total Water level Data: al

Pt. Atkinson - (1949-2006) (51yrs)

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Extreme Value Analysis Statistical Technique (Coles, 2001).

Methodology ..

TWL Extremes

(i) Annual Maxima (GEV)

Wind Extremes

(ii) Peak over Threshold (GPD)

μ = Location σ = Scale ξ = Shape

Parameter Estimation

For a given set of maxima the parameters are estimated via the Maximum Likelihood Estimation (MLE) method.

The Extremes Toolkit (Gilleland and Katz (2005)

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Methodology

Step 1 : Application of GEV to project Return Levels without Climate considerations:

Project Return Levels based on the Annual Maxima Residuals.

Generalised Extreme Value Distribution (GEV).

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Extreme Value Analysis in the presence of Climate Variability Covariates (X)

Methodology..

(μ, σ, ξ ) = f( X = MEI, PDO, NOI, ALPI, PNA)

Location Parameter Scale Parameter Shape Parameter

Effect of Natural Climate Variability on Extremes.

Step 1: Identify the CV indices that shows significant improvement in the model fit with respect to the no-covariate case.

Add each CV variable as Covariates in the Location(µ) , Scale (σ) and shape ( ξ) parameter and test for significant model improvements through a Likelihood ratio test.

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Methodology

Generalised Extreme Value Distribution (GEV).

Step 2 : Investigate the influence of Cyclic Climate Variability Phenomena on return level projections:

Station 7120 : Victoria Harbour

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Effect of Natural Climate Variability on Extremes.

Most climate indices are closely related

Redundancy test was performed

Step 2: Systematically add each variable isolated in step (1) in to the model and eliminate the ones that does not improve the model fit significantly with respect to the former.

Methodology

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Effect of Natural Climate Variability on Storm surge recurrences.

Redundancy test

Methodology

NOI

NOI + PNA

Station 7120 : Victoria Harbour

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Effect of Natural Climate Variability on Storm surge recurrences.

Final Model Consideration with CV effects after the redundancy test

Methodology

Station 7120 : Victoria Harbour

μ (x) = 57.5 + 7.04(PNA)-2.28(NOI)

σ (x) = 10.5

ξ(x) = -0.368

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Methodology.

• The definitions are based on the Environment Canada classification scheme.

Step 3: Climate Indices Conditional on 3-dominant Climate State

(i) Warm ENSO

(ii) Neutral

(iii) Cold ENSO

Effect of Natural Climate Variability on Extremes.

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Results

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Climatic patterns governed by PNA, NOI and MEI has a significant influence on storm surge occurrences in the region.

Results

Sensitivity of Storm Surges to Climate Covariates

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Results

Effect of Natural Climate Variability on Storm surge recurrences.

Estimated return levels and 95% confidence intervals under ENSO conditions. Results for no climate consideration are included for comparison purposes

Station 7120 : Victoria Harbour

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All stations indicate higher residual water-levels during warm ENSO episodes.

Results Storm Surges with 1% exceedance in each year with CV effects

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7

89

1011

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Extreme Directional Wind recurrences with climate Covariates.

Results.

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Directional Wind Recurrences at YVR with climate covariates.

Results.

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Case Studies

(i) December 16th 1982 Extreme Event

(ii) February 4th 2006 Extreme Event

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December 16December 16thth 1982 Storm Event 1982 Storm Event examples of impacts…examples of impacts…

Damage to Mud Bay during 1982 flooding Damage to Westham Island

Serpentine Dike DamageDamage along King George HWY in Surrey

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December 16th 1982 Storm Event

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Results.Extreme TWL Recurrences With CV effects at Pt. Atkinson

(1) (2) (3) (4) (5) (6)

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February 4February 4thth 2006 Storm Event 2006 Storm Event examples of impacts…examples of impacts…

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February 4th 2006 Storm Event : TWL Event

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February 4th 2006 Storm Event : Wind Direction

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February 4th 2006 Storm Event : Wind Speed

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2006 event Recurrences viewed under Climate Variability

Extreme TWL Recurrences and Extreme Storm Recurrences are not in phase

• Warm ENSO phase favors extreme TWL & Residuals

• Cold ENSO phase favors extreme windstorms

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Conclusions..

Climate Variability has significant effects on extreme sea levels and windstorm recurrences in Southern BC.

All stations in coastal BC indicate an increase in the Residuals during warm ENSO episodes.

Climatic patterns represented by PNA, NOI and MEI climate indices has a significant influence on storm surge occurrences in the region

A Cold ENSO phase could result in more frequent windstorms in the study region

Extreme TWL Recurrences and Extreme Wind-Storm Recurrences are not in phase in Southern BC.

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photo courtesy of Michael Brownphoto courtesy of Michael Brown

Policy decisions are mainly driven by potential societal impacts

resulting from climate variability and change, and not the climate

change itself

Changing extremes

due to CC and CV effects are the

most damaging

Therefore it is strongly recommended to account for the effects of

CC and CV in the analysis of Extremes leading to new policy

decision for adaptation and design criteria.

Policy decisions are mainly driven by potential societal impacts

resulting from climate variability and change, and not the climate

change itself

Changing extremes

due to CC and CV effects are the

most damaging

Therefore it is strongly recommended to account for the effects of

CC and CV in the analysis of Extremes leading to new policy

decision for adaptation and design criteria.

““February 04February 04thth 2006 Storm Impact at Boundary bay “ 2006 Storm Impact at Boundary bay “

Picture provided by the Picture provided by the Fraser Delta’s Engineering DepartmentFraser Delta’s Engineering Department

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Acknowledgements Ben Kangasniemi , BC Ministry of Environment.

Rick Thompson, Bill Crawford , Scott Tinis, IOS Sidney BC

Eric Gilleland NCAR,Boulder CO, USA

Bill Taylor and Mark Barton Environment Canada

Trevor Murdock & Pacific Climate Impact Consortium

Research Support & Contributions

BC Ministry of Environment Environment Canada DFO & IOS Sidney BC Pacific Climate Impact Consortium (PCIC) National Center for Atmospheric Research (NCAR), USA Co-op Social Science University of Victoria BC Ministry of Labour and Citizens’ Services

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Thank you… feedback?