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Proposed Hazard Module
Expert Panel Open Meeting
Austin, TexasMarch 13, 2014
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Agenda
Introductions Overview Proposed Hazard Module
Wind Wave and Surge Flooding
Timing and Delivery of Hazard Module Future Work Q&A
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Introductions
Sam Amoroso, Ph.D. P.E., S.E. Forte & Tablada, Inc.
Bob Bailey, Ph.D., P.E. Exponent, Inc.
Bill Coulbourne, P.E. Coulbourne Consulting
Andrew Kennedy, Ph.D. University of Notre Dame
Doug Smith, Ph.D., P.E. Texas Tech University
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Overview
1st Open MeetingAustin, August 22, 2013
Develop Framework Plan
2nd Open MeetingCorpus Christi, December 10, 2013
3rd Open MeetingAustin, March 13, 2014
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1st Open Meeting
Panel Member Backgrounds
The TWIA expert panel has been appointed under Insurance Code §2210.578 and 28 Texas Administrative Code §§5.4260-5.4268. The panel’s purpose is to develop ways of determining whether a loss to TWIA-insured property was caused by wind, waves, tidal surges, or rising waters not caused by waves or surges.
After the panel completes its work, the commissioner will consider the panel’s findings and publish guidelines that TWIA must use to settle claims.
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2nd Open Meeting
Present Preliminary Overall Methodology Initial Focus: Residential Slab Only Claims
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Preliminary Overall Methodology
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Proposed Hazard Module
Wind
Dr. Doug Smith Objectives Methodologies Model Classes and Investigations Recommendations
Wave and Surge Flooding
Dr. Andrew Kennedy Wave and Surge Definitions Model Requirements Technical Requirements Coupled Wave and Surge Models Wave and Surge Measurements
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Wind
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Objectives for Hazard Module
Goals Site Specific:
wind speed time history wind direction time history surge time history wave time history
Minimum of error Used to predict damage to
individual structure as the storm passes
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Hazard Timing
12 m/s
75 deg
10 ft 2.2 ft
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Hazards Module Flow Chart
Steps Collect Hurricane Wind Field
Data over Life of Storm. Develop Global Hurricane
Wind Field. Use the hurricane wind field as
input to surge model and wave model.
Obtain time correlated histories.
Refine the time histories. Final time histories for
vulnerability module.
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Wind Hazard Component
Two purposes Input for surge and wave module Input for wind damage prediction module
Wind speed and direction at mean roof height (MRH) Adjusted for upwind terrain
MRH
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Methodologies
Physical Measurements Wind Surge
Models Wind field model Surge model Wave model
Combination of measurement and modeling
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Physical Measurement
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Model Classes
Parametric Easy to use numerical model. Requires minimal computational power.
Observational Wind field constructed using objective analysis from
surface wind speed measurements. Requires minimal to moderate computational resources.
Dynamical Numerical Weather Prediction Wind field constructed from sophisticated equations sets. Requires significant computational resources.
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Model ClassesClass Examples Time
ResolutionHorizontal Resolution
Dir. & Speed Accuracy
Parametric HollandModified HollandWilloughby
User selectedUser SelectedUser Selected
User SelectedUser SelectedUser Selected
Observational HRD H*Wind1
LNSS WFA2
OWI IOKA3
3 hrs10 minutes30 minutes
4-5 km500 m5 km ±20° ±2m/s
Numerical Weather Prediction
HWRF4
GFDL56 hrs6 hrs
9 km5 km
1Hurricane Research Division Hurricane Wind2Letchford Norville Schroeder Smith and Associates Wind Field Analysis3Oceanweather, Inc Interactive Objective Analysis System4Hurricane Weather Research and Forecasting5Geophysical Fluid Dynamics Laboratory
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Model Investigation
Models Holland (symmetric)
with translation Modified Holland
(asymmetric) with translation
H*WIND LNSS WFA
Evaluation Criteria Model output wind
speed compared to surface observations
Desire minimum error Hurricane Ike
model observederror V V
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Hurricane Ike at Landfall
A
C
B
D
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Surface Observations for Error Investigation
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TTU 110 Center of Storm
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TTU 110 Time History Comparisons
C D
BA
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TTU 102 NE Wind Max
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Model Comparison
C D
A B
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TTU 220 West of Track
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Model Comparison
C
BA
NO LNSS WFA FORTHIS COMPARISON
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Bulk Errors
C D
BA
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Errors at H*Wind Time Steps
C
BA
NO LNSS WFA FORTHIS COMPARISON
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Errors at All LNSS WFA Steps
C
BA
NO H*WIND FORTHIS COMPARISON
C
BA
NO H*WIND FORTHIS COMPARISON
C
BA
NO H*WIND FORTHIS COMPARISON
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Errors at time steps where both H*Wind and LNSS WFA exist
C
BA
D
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Summary
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Recommendations
Use an observational wind field for the hurricane wind field model.
High spatial and temporal resolution Produce wind speed and direction time histories with
minimum of error Increase the number of surface observations
contributing to the observational wind field (e.g. using pre-positioned or mobile platforms) to improve accuracy.
Embed the observational wind field in a larger synoptic model for surge and wave modeling.
Use local observational wind field analysis to refine wind time histories if necessary.
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Storm Surge Flooding
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Wave and Surge Hazard
Texas has experienced numerous catastrophic wave and surge events during hurricanes. The two most notable are:
1900 Great Galveston Hurricane Hurricane Ike (2008)
Thousands of buildings were destroyed in each of these storms.
Particularly for post-storm slab cases, knowledge of wave and surge hazard levels (storm surge, waves heights) is needed to help separate wave/surge and wind damage.
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Models and Measurements
Both direct measurements and models will be important in establishing wave heights and surge elevations.
For TWIA, both are most important in built up regions with insured properties.
Models and measurements will both be used to determine hazard levels (waves and surge) at properties.
Resulting hazard levels will aid in adjusting claims.
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Wave and Surge Definitions
Separate inundation into waves and surge
Surge is the slow variation of average water levels over periods of 10 minutes or longer
Waves are the faster variation of water levels
Like waves at the beach Typically 5-20s periods
dominate in hurricanes
At a given location wave and surge properties will define the hazard.
When combined with the structural properties, these will allow damage estimates.
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Model Requirements (Waves and Surge)
To be most useful to TWIA, models will need to have certain properties relating to accuracy and usability.
There may be more than one choice of model that meets requirements.
Models will need to be set up well before any storm so they may be run quickly after the storm.
Models should give predictions of waves and surge that are as accurate as possible for a hurricane impacting the Texas Coast. The region most important for accuracy is on normally dry
ground, at insured properties. Models should be validated against historic storms.
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Technical Requirements (Wave and Surge Models)
Models should not just include the Texas Coast, but will need to encompass the Gulf of Mexico.
Grid resolution needs to be as fine as possible in the vicinity of insured properties (20-80m).
Wave and surge models should be tightly coupled. Models should be easily modified to account for post-
storm changes/erosion to dunes and shoreline. Model should have an accurate wind field model that is
consistent with the wind hazard module. Surge model should include tides.
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-96.6 -96.5 -96.4 -96.3 -96.2 -96.1 -96.0 -95.9 -95.8 -95.7 -95.6 -95.5
Longitude (deg)
28.2
28.3
28.4
28.5
28.6
28.7
28.8
Lat
itu
de
(deg
)
Example Topographic Detail – Coarse Grid
Source: Bailey, 2010, “Probable Maximum Surge and Seiche Flooding,” Presentation to the Nuclear Regulatory Commission.
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Example Topographic Detail – Fine Grid
-96.6 -96.5 -96.4 -96.3 -96.2 -96.1 -96.0 -95.9 -95.8 -95.7 -95.6 -95.5
Longitude (deg)
28.2
28.3
28.4
28.5
28.6
28.7
28.8
La
titu
de
(d
eg)
Source: Bailey, 2010, “Probable Maximum Surge and Seiche Flooding, ” Presentation to the Nuclear Regulatory Commission.
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Example of High Resolution Hurricane Ike Simulation using SWAN+ADCIRC SWAN computes waves, ADCIRC computes surge. May not be the only model choice that could give good
results. 18 million element simulation using hindcast winds (high
accuracy reconstruction). Resolution down to 20m in some complex areas. Runs on parallel computer (like all high resolution
simulations). Tides included. Comparisons against high water marks, NOAA gauges,
rapidly installed gauges.
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Grid Resolution on the North Gulf Coast
Maximum Surge Levels
Source: Hope et al. (2013). JGR-Oceans, 118, 4424-4460.
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Model Comparison with Ike High Water Marks
Two shades of green indicate model predictions to within ±0.5m (1.6 feet)
Very good accuracy around Texas Coast
Source: Hope et al. (2013). JGR-Oceans, 118, 4424-4460.
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MeasuredSWAN
STWAVE
Model Comparison with Wave Height
• All data are offshore of land
• Overland accuracy lower
Scatter Index: 0.2603 (lower is better)
Source: Hope et al. (2013). JGR-Oceans, 118, 4424-4460.
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Loss of Accuracy with Fewer Grid Points 18 million vs 827,000 element simulations R2 decreases from 0.823 to 0.758 (higher is better) RMS error from 0.284m (0.9ft) to 0.356m (1.2ft)
Medium Resolution
High Resolution
Two shades of green indicate model predictions to within ±0.5m (1.6 ft)
Source: Kerr et al. (2014a). JGR-Oceans, 118, 4633-4661.
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Loss of Accuracy with Very Few Grid Points 827,000 (ADCIRC) vs 185,000 element (SLOSH) R2 decreases from 0.716 to 0.555 (higher is better) RMS error from 0.486m (1.6ft) to 0.961m (3.2ft)
Low Resolution
Medium Resolution
Different Models Used (ADCIRC vs SLOSH)
Source: Kerr et al. (2014b). JGR-Oceans, 118, 5129-5172.
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Coupled Wave and Surge Models
Inclusion of wave radiation stresses into surge model is necessary to achieve maximum accuracy.
Gives Wave Setup in nearshore. In high resolution model Ike simulation, R2 decreases from
0.832 to 0.785 if waves are not included. RMS error increases from 0.284m (0.9ft) to 0.334m (1.1ft).
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Wave and Surge Measurements
Direct measurements of waves and surge near insured properties will help to improve evaluations of hazard levels.
Continuously recording pressure measurements with high temporal resolution will provide the best combination of accuracy and cost efficiency. Instruments will likely need to be rapidly installed
pre-storm, based on the storm track. High Water Marks can give good data post-storm. It may prove best to couple with external partners to
collect data.
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Example USGS Measurements
Bolivar Peninsula, Direct Oceanfront. Installed directly before storm. Processed data provides evaluation of both
surge elevation and wave height over time.
Source: East et al. (2008). USGS Open-File Rep. USGS 2008-1365.
51Source: Doran et al. (2009), USGS Open-File Rep 2009-1061.
Post-Storm Update of Model Topography
Can be large changes to dune and other elevations that can affect model performance.
Updated bathymetry essential – likely with airborne lidar surveys.
Should be quick – within the first week post-storm.
Pre-Ike Post-Ike Difference
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Summary: Wind and Storm Surge Features Use an observational wind field for the hurricane wind field
model. Increase the number of surface observations contributing to the
observational wind field to improve accuracy. Embed the observational wind field in a larger synoptic model
for surge and wave modeling. Wave and surge models should include the Texas Coast and the
Gulf of Mexico. Grid resolution needs to be as fine as possible in the vicinity of
insured properties (20-80m). Wave and surge models should be tightly coupled. Models should be easily modified to account for post-storm
changes/erosion to dunes and shoreline. Surge model should include tides.
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Timing and Delivery of Hazard Module
Other major components (damage, economic loss) rely on outputs from hazard module.
The panel understands that, by law, TWIA must act on all claims within 60 days from when they are filed. The hazard module must therefore produce results in
a time period much less than 60 days. This deadline imposes a very aggressive schedule and
will dictate choices as work performed in a short time frame differs from what can be done with less time pressure. The module will need to be set up and tested before
the start of hurricane season, and be ready to ingest storm data.
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Preliminary Overall Methodology
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Next Step – Damage Estimation Module
Proposed Module… Based on Probabilities of
Component Failure (Wind) or Probability of Structural Collapse (Surge and Wave)
Coupling of Component Damages Time Histories of Damage
estimated from Hazard Time Histories
Present proposed module during next Open Meeting (May 2014).
Damage Estimation Module
Damage Estimate forEconomic Loss Module
BuildingSpecific
Information
Wind, Surge &Wave Time
Histories
BuildingVulnerabilityFunctions
Database ofObserved Damage
from SurvivingStructures
Damage Functionsfor
Building Components
Peak WindSpeed
Surge & WaveHeights
Damage Estimatefor Building Components
from Model
Damage Estimatefor Building Componentsfrom Damage Functions
Refinement ofDamage Estimate
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Future Work
Calibration and Validation of Model Compare Ike damage with model predictions for same
location. Adjust model as necessary. Conduct randomized model validation using claim
data from Hurricane Ike. Present findings in a future Open Meeting (June 2014)
Finalize recommendations and present to TDI.
Continue with development of a method or model to estimate damage to commercial properties starting with slab-only cases.
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From the Expert Panel Outline of the Overall Methodology dated 18 November 2013:
Need contract in place to acquire post-storm LIDAR imagery.
Need contract in place to conduct high wind and storm surge modeling post-storm.
Need methods in place to collect high quality real-time storm surge and wind field data during storm.
TWIA Action Items
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Q&A
