MODELLING CATASTROPHIC COASTAL FLOOD RISKS AROUND THE WORLD

OUTLINE MOTIVATION What we do Why we do it METHOD How we do it CASE STUDY I CASE STUDY II From earthquakes, hurricanes, and floods to terrorism and infectious diseases, RMS helps financial institutions and public agencies understand, quantify, and manage risk Copyright 2016 Risk Management Solutions, Inc. All Rights Reserved. June 27, 2016 2

Our view of risk includes a comprehensive understanding of perils, exposure to those perils and the translation of risk into financial terms for our clients WHY DO WE MODEL STORM SURGE? Coastal flooding from storm surge is one of the perils we model 3

NOAA (2013) an additional 11 million people will be living along the (US) coast by 2020 bringing the total to ~134 million. Texas A&M University and Yale University - By 2030, built up lowelevation coastal land in China is set to nearly quintuple to 63,600 sq km, an area nearly as large as the Netherlands and Belgium combined. Hurricane Sandy Image: Master Sgt. Mark C. Olsen, U.S. Air Force Typhoon Haiyan Image: Noel Celis, AFP 4

HOW WE DO IT Various components to our surge model including: Wind forcing Surge - Mike 21FM Defences Inundation Stochastic Track Set thousands of years per basin Surge (and Mike 21FM waves) with surge model Mike calibrated and calibrated and validated with validated with historical data historical data Nearshore and Defence models Inundation model 5

Typhoon paths curve up from the south either hitting the South coast or bypassing to the east (no landfall, spin off into Sea of Japan) or the west where they either curve round to hit the west coast or landfall on china. KOREAN SURGE 7

BUILDING A MESH - CONSIDERATIONS Over 2000 islands and complex bathymetry 8

TIDE AND SURGE: MAEMI We calibrate our model using historical tide and surge data. 9

MAEMI INUNDATION USING CURRENT DEFENCES 10

MAEMI INUNDATION USING HISTORICAL DEFENCES 11

RMS US HURRICANE SURGE MODEL Model covers entire length of US East coast from Maine to Texas 5,800 km of coastline (Atlantic: 3,200 km, Gulf: 2,600 km) Subdivided into 18 sub-regional meshes Different regions present different modelling challenges (data availability, complex topography, sea defences,...) Explicitly modelling coastal inundation for thousands of synthetic hurricane events Also model historical events to estimate damage & financial losses 13

CASE STUDY: ZOOM TO NEW ORLEANS Large parts of New Orleans are below sea level System of levees keeps the city dry But these can fail e.g. Hurricane Katrina Failure through overtopping, scour & breaching Defence overtopping eroded foundations and caused breaches Model needs to account for overtopping/breaching in New Orleans 14

Advantages High-res model of inundation in NO Explicitly account for failures of individual reaches But Need to change the elevation of breached defences for every storm (100s of storms ) Need very high res mesh Computationally expensive! Evolution of breaches cannot be controlled (elevation can t be modified during simulation ) NEW ORLEANS CITY MESH Very high resolution: explicitly resolves defences Defence breaches are modelled by lowering the height of levees/defences at breach locations By how much? Calculated based on water depth, defence characteristics, etc. Used to determine hazard for all areas inside the New Orleans protection system Computationally expensive! 15

Katrina, 23-30 Aug 2005 Landfall rating: Category 3 (Louisiana) Max surge elevation: 29 feet (!) HURRICANE KATRINA Katrina footprint from historical reconstruction : modelled (filled contours) vs observed (overlaid circles) surge Notes: Costliest natural disaster in US history Category 5 storm less than 24 hrs before landfall 50 total levee breaches Defence system subsequently underwent large-scale upgrade 16

SUMMARY www.rms.com nicola.howe@rms.com RMS integrates the MIKE 21 hydrodynamic, time-stepping storm surge model into our cyclone models. We validate our models using historical surge events. In order to run the thousands of stochastic wind tracks which generate surge we use the Linux implementation of MIKE. Our models enable an accurate, comprehensive view of coastal flood risk down to the local level. 18

www.rms.com nicola.howe@rms.com Thank you for listening. Any questions? 19