risk on the rise: understanding and managing coastal flood risk

1Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. April 15, 2023

RISK ON THE RISE

UNDERSTANDING AND MANAGING COASTAL FLOOD RISK Robert Muir-Wood and Juergen Grieser


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MEET THE EXPERTS

Robert Muir-Wood, Ph.D.

Chief Research Officer

Juergen Grieser, Ph.D.

Director, Model Development

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BOUNDARY IS THE

RISK CONCENTRATORS

WHY THE LAND-SEA

BIGGEST OF ALL

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EVENTS WHERE MORE THAN 50% OF THE LOSS WAS COASTAL

Thai Floods

Superstorm Sandy Tohoku EQ and Tsunami

Hurricane Katrina

5Copyright © 2015 Risk Management Solutions, Inc.

HOW LAND VALUES INCREASE AT THE COAST

The amenity value of the same property increases significantly at the coast.

The most expensive property is then also the most vulnerable.

http://www.gradschool.psu.edu/diversity/mcnair/papers2003/majorpdf/

Data from Stone Harbor and Avalon, New Jersey, 2002/2003Photos courtesy of Airbnb.com

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http://www.gradschool.psu.edu/diversity/mcnair/papers2003/majorpdf/

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COAST-SPECIFIC EXPOSURE CATEGORIES

Hotels and condosAirports

Ports Marinas

Refineries

Power plants


THE PDF OF GLOBAL EXPOSURE VALUE BY ELEVATION (ABOVE HIGH-WATER LEVEL)

For first meter:average value = $1Bn/mm

However, pre-existing safety marginsgive critical thresholding effects.

Reconstructed from Anthoff et al., (2006)

1000

750

500

250

0

0 2 4 6 8 10

Meters elevation asl

Billions of dollars, U.S.


1000-YEAR WATER HEIGHTS FOR AUSTRALIA

‘Coastal’ should not be measured in ‘distance’ (D2C) but instead in elevation (H2HW).

‘Elevation at risk’ varies by location.

‘Coastal’ is a probabilistic concept.

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BOTH SEA LEVELS AND LAND LEVELS

COASTAL RISK IS EXPANDING INLAND

ARE CONTINUING TO CHANGE


‘Coastal’ is a probabilistic concept.

Many coastal cities are sinking because of urban groundwater extraction.


10-Foot Tsunami

SEVERE PHYSICAL DAMAGE POTENTIAL FROM COASTAL FLOOD HAZARDS

Damage from a 10-foot storm surge is little different from that of a 10-foot tsunami—note that debris can be a principal driver of severe damage. 10-Foot Storm Surge


SEVERE PHYSICAL DAMAGE POTENTIAL FROM COASTAL FLOOD HAZARDS

Damage from a 20-foot storm surge is little different from that of a 20-foot tsunami—note that surge will have bigger waves.

20-Foot Storm Surge 20-Foot Tsunami


PHYSICAL DAMAGE IS NOT NECESSARILY THE MAIN DRIVER OF LOSS

• Spills

• Contamination

• Loss of production

• Local liability (18.5 million people; see report)

Meraux Refinery near New Orleans after Hurricane KatrinaPhoto: FEMA / Patsy Lynch

Fukushima Daiichi Plant after Tohoku Japan EarthquakePhoto: REUTERS/Ho New

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YOUR FLIGHT HAS BEEN CANCELLED BY HIGH TIDE

Bangkok Sendai, 2011

Sandy, La Guardia Grand Bahama x 5 in 15 years

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COASTAL FLOOD HAZARDS ARE COMPLEX TO MODELWHAT DOES IT TAKE TOUNDERSTAND TSUNAMI?

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Philippines Sea Plate

Eurasian Plate/ Sunda Block

Yangtze Plate

90 mm/yr

MANILA ARC

Ref:Hsu et al. (2012)

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TSUNAMI MODELING COMPONENTS

Identify Source Subduction

Zones

Event Generation

Ocean Wave Propagation

Coastal Inundation

Source Characterization

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WHERE DO WE EXPECT TO SEE COASTAL INUNDATION?

Image: S. Astill et al (2013)

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WHERE DO WE EXPECT TO SEE COASTAL INUNDATION?

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Hong Kong

MW9 TSUNAMI FROM THE SOUTHERN LUZON ARC SUBDUCTION ZONE – SOUTHERN CHINA & HONG KONG

0.1 - 1.5 m

1.5 - 3.0 m

3.0 - 4.5 m

4.5 - 6.0 m

Industries

Tsunami height

Source: Esri, DigitalGlobe,DeoEye, I-cubed, Earthstar Geographic, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, OISP, swisstopo, and the GIS User Community

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COASTAL FLOOD HAZARDS

INNOVATIONS IN MODELING

ARE COMPLEX TO MODEL

SURGE FLOOD IN JAPAN


THERE’S NO SURGE WITHOUT WIND

Most of the typhoons hitting Japan have already started transitioning to extratropical storms.

Disregarding transitioning can lead to errors in maximum surge height of up to 1.5 m.



Most of the typhoons hitting Japan have already started transitioning to extratropical storms.

Disregarding transitioning can lead to errors in maximum surge height of up to 1.5 m.

Reliable wind modeling including extratropical transition is crucial.



But where is the wind?

How strong is it?

And in which direction does it blow?

Classical typhoon wind

footprint

Published in Loridan et al. (2014, 2015).



But where is the wind?

How strong is it?

And in which direction does it blow?

Classical Typhoon wind

footprint

Transitioning wind footprint

Published in Loridan et al. (2014, 2015).


BATHYMETRY AND THE SHAPE OF THE COAST

Wind produces currents and waves.

Deep Water Shallow Water

WindWind




The coast produces the surge.


Low Surge

WindWind




The coast produces the surge.


Low Surge High Surge

WindWind



The Japanese coastline is extremely complex.

The coastline can diverge or funnel currents.



From a surge perspective, exposure is concentrated at the worst locations.

HiroshimaOsaka

NagoyaTokyo


WHAT IF VERA (1959) HIT SOMEWHERE ELSE?

Only detailed hydrodynamic modeling can reveal the risk.




Tokyo




HiroshimaTokyo


DEFENCES MAKE THE DIFFERENCE?

New Orleans: more than 50 breaches during Hurricane Katrina (2005).



• Japan is very well defended.

• More than 97% of typhoons hitting Japan do not cause coastal inundation.

• This can lead to a wrong feeling of safety.

• The probability of a 1000-year surge event happening within the next 50 years is about 5%.

WE HAVE TO LIVE WITH THIS RISK



Absolutely…

…as long as they stand.


WAVES

Wave modeling is far more complicated than surge modeling

Waves interact with each other in complex ways

+ =


SURGE, TIDES, AND WAVES INTERACT



There are many processes, such as:

Shoaling,

Refraction,

Defraction,

Reflection...



During surge events, higher waves hit the defences.

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DEFENCES MAKE THE DIFFERENCE?Yokohama: breaching increases the losses in this case from 40 million to 17 billion Yen.

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DEFENCES MAKE THE DIFFERENCE?Yokohama, breaching increases the losses in this case from 40 million to 17 billion Yen.

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DEFENCES MAKE THE DIFFERENCE?Yokohama, breaching increases the losses in this case from 40 million to 17 billion Yen.


THE IMPLICATIONS OF ‘COASTAL RISK’

• The biggest concentrations of risk and gradients of risk are coastal

• Coastal risks vary dramatically with elevation

• Always need location/address level data

• Need ‘state of the art’ modeling of the hazards – storm surge and tsunami & the defences

Under- accelerating sea-level rise defences will not keep pace with the risk until after the disaster.

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RISKS WELL

PORTFOLIO WELLAND YOU WILL BE MANAGING YOUR

MANAGE YOUR COASTAL

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