Models Come To Life

In Katrina Assessment

By Mohit Pande and Glen Daraskevich

On Aug. 29, Hurricane Katrina entered the record books as thecostliest natural disaster in U.S. history. While Katrina's impactclearly extends far beyond the catastrophe modeling and insuranceindustries, here we focus on observations and lessons learnedduring our initial damage surveys through parts of Florida,Alabama, Mississippi and Louisiana.

We led two of our post-disaster survey teams of engineersdispatched to areas affected by the storm within days of Katrina'slandfall on the Gulf Coast of Louisiana.

Typically, our damage survey teams fly in and stay in thehardest hit areas, and subsequently fan out. This was impossible inthe case of Katrina, where airports were closed and hotels stillstanding were either closed or filled to capacity.

Instead, our teams flew into Pensacola, Fla., and worked theirway west across Katrina's track. All of the impacted coastal areasof Florida, Alabama and Mississippi were surveyed. New Orleans wasstill largely inaccessible to any but emergency workers, but wewere able to survey from Slidell--across the north side of LakePontchartrain-some of the areas with the worst wind damage inLouisiana.

The effort was far from a laboratory exercise, as many of theaffected areas lacked power, running water, food and street signs.Moreover, there were curfews in effect, as well as a chaotic floodof evacuees, emergency responders, law enforcement and militarypersonnel.

The primary objective of the damage survey is to validate ourmodeled scenarios with actual observations of the damage. Ourclients can then better serve their customers, by using thisinformation to triage their claims and redeploy their forces tocover areas with the highest average claims severity level.

Our other objective is to record details of the actual damage touse along with detailed claims data to validate and enhance variousaspects of the model.

For instance, our damage surveys after each of the four stormsin Florida last year found that repair costs were multiplying dueto the cumulative effect of the storms on the regional economy. Asa result, we modified our 2005 model to enable clients to accountfor demand surge on an aggregate as well as an occurrencebasis.

Hurricane Katrina was both very intense and very large.Katrina's hurricane force winds extended out 120 miles on eitherside of the storm and more than 150 miles inland.

Our teams observed wind damage as far east as Pensacola, Fla.,and as far west as Baton Rouge, La. Traveling inland, damageextended north to Jackson, Miss., and east along Interstate 20 toMeridian, Miss., almost 150 miles from the coast.

Generally, the wind damage was consistent with what we expectedfrom a storm of this size and intensity, and consistent withestimates produced in real time by our hurricane model.

The survey teams selected, at random, multiple three-by-three orfour-by-four block sections of each town. They counted the actualnumber of houses and businesses and estimated the percentage ofdamage to each structure. Each team typically completes 10-to-15surveys a day.

The median wind-speed footprint generated by our hurricane modelserved as a guide for planning our survey routes. Here are some ofthe highlights of what we found:

o On the fringes of the damage footprint in Pensacola, Fla., andBaton Rouge, La., most of the damage was non-structural. Missingroofing shingles and damage to siding were common.

o There were also cases of fallen trees impacting residentialproperties, which is typical for the 60-to-70 mph sustained windsexperienced in these areas. In the Mobile, Ala., area, with itsnumerous neighborhoods wooded with mature southern yellow pines,downed trees were a common cause of loss.

o Property damage became more severe as the teams traveledcloser to the center of the storm's path.

Hurricane Katrina made landfall southeast of New Orleans,sparing the city its most intense winds. Instead, Mississippi'scoast bore the brunt both of Katrina's highest wind speeds andhighest storm surge, impacting the well-populated areas of Gulfportand Biloxi.

Pascagoula, Miss., and Slidell, La.--which experienced maximumsustained winds of 90-to-100 mph--suffered significant damage.While parts of Slidell were ravaged by storm surge, the town alsosustained significant wind damage.

o Damage to commercial structures in these areas was widespread,particularly to cladding and roofs. As indicated by our hurricanemodel and confirmed through our observations, we estimate that winddamage will play a large role in the overall insured loss in thecity.

o While the most severe wind damage occurred within a 25-to-30mile swath to the right of Katrina's track, severe wind damage wasobserved well inland in Wiggins, Miss., and even as far north asHattiesburg.

o As expected, buildings of inferior construction fared poorlyand light metal structures fared the worst. Unreinforced masonry--awidely used construction type in the region--also performedpoorly.

o Use of vulnerable cladding materials such as ExteriorInsulation and Finish Systems exacerbated damage to hotels, casinosand other commercial structures.

Only three weeks after Hurricane Katrina, the long-term effectson the Gulf States and their economies remain unclear. Ourground-level view confirmed early expectations that Katrina will benot only an unprecedented event for the insurance industry but ahumanitarian disaster on an immense as well as individualscale.

While our survey results are intended to assist companies inanalyzing the impact and managing their response, some of the moreimmediate activities we engaged in on the ground--offering ahomeowner a gallon of water, a newspaper or a flashlight--were themost valuable services we provided.

Mohit Pande is senior wind engineer atBoston-based AIR Worldwide Corp., and GlenDaraskevich is an assistant vice president in AIR'sresearch and modeling department.

Caption:

Many high-rise commercial structures in the Gulfport and Biloxi,Miss., areas experienced storm surge damage on lower floors andwind damage on upper floors.

Photo By AIR Worldwide Corp.