By Eric Berger - Chron.com
When a really strong hurricane next blows through Houston, its winds - not its waters - pose the greatest threat to inflict damage unimagined by most living here.
Tropical Storm Allison produced a virtually worst-case flooding scenario in 2001, racking up $5 billion in damages. Hurricane Ike produced a destructive surge of water, and its U.S. damages came to $29.5 billion.
Such water damages, however, are nothing compared to the threat of a mighty blow, which Houston has not truly experienced since 1915.
A new, but unpublished, study reveals the true scope of damage Houston could sustain from a major windstorm if a hurricane were to strike Galveston Island and barrel on through Harris County.
According to the analysis by Civil Tech Engineering, a Category 4 hurricane moving northwest at 10 mph would cause $309 billion in property damage and $65 billion in business interruptions.
The study predicts nearly 800,000 homes in Harris County would be severely damaged or destroyed - 80 percent of the total housing stock - along with 50,000 commercial buildings.
"That's just wind damage," said Melvin Spinks, president of Houston-based Civil Tech. "It doesn't include flooding from rain or surge."
Spinks didn't do the study to scare people. His firm is one of the state's only authorized users of a powerful federal modeling tool called Hazus, created to estimate the physical, economic and social impacts of disasters.
At the behest of the city of Houston, in 2010, his firm used the best available data on local elevations, housing stock quality, tree coverage and a host of other variables to provide the best estimate yet of the region's potential for wind damage from 90 different scenarios.
The firm's modeling showed that, based upon angle, location and speed, large Category 3 hurricanes striking Harris County today would produce a range of wind damages from $40 billion to $160 billion. For Category 4 storms, the model produced wind damages ranging from $77 billion to $385 billion.
Some Category 5 storms - so rare that only three have ever struck the United States - produced damages in excess of half a trillion dollars.
"We've always known there was significant risk from some of these much larger storms," said Sharon Nalls, the city of Houston's emergency management coordinator.
What isn't clear, she said, is whether residents understand that risk.
Better assessment tools
That's partly why the city commissioned the study. Since its completion in May 2010, the results have been used to prepare better tools for home and business owners to assess their risks.
In the next couple of weeks the city will roll out two new websites, Nalls said.
One is an update of its "Houston Hide from the Wind" website, offering real-time estimates of wind speeds, by ZIP code, based upon National Hurricane Center forecasts. The website will now include information for Harris and surrounding counties, not just the city.
Secondly, the city will launch a website on which residents can enter an address to view the potential wind, flooding and surge threats to their property from various strengths of storms.
After the regional evacuation from Hurricane Rita produced a massive traffic jam in 2005, city and county officials launched a campaign to better inform residents about who should go and who should stay.
The new wind damage data, Harris County Judge Ed Emmett said, doesn't change the basic message - run from the water, hide from the wind.
"In Harris County, residents who are not in a potential storm surge zone are asked to shelter in place," he said. "The strong winds associated with a hurricane might damage property, but they pose little danger to life. Once a storm has passed, residents can then secure their property and leave."
Nalls said the city also will use the wind study to better prepare the region for a windstorm.
According to Annie Ding, who led the study for Civil Tech and also modeled mitigation, the most effective strategy to reduce wind damage is installing storm shutters to protect windows from flying debris.
However, Nalls noted, there has been no discussion about strengthening residential building codes to require storm shutters.
The code situation is even worse in unincorporated areas of Harris County, where there is no statewide building code to govern the construction of homes to protect from hurricane damage.
Building codes critical
Earlier this year, the Institute for Business & Home Safety, an insurance industry group that conducts research to promote more durable construction, ranked the 18 Gulf and Atlantic states on building codes. Texas was 16th on the institute's list, ahead of only Delaware and Mississippi.
Statewide codes are critical because they allow builders to construct homes to a single standard, said Wanda Edwards, a code expert with the institute.
"It levels the playing field," she said.
Houston hasn't had to deal with a windstorm in a long time.
In 1983 Alicia hit Galveston as a Category 3 hurricane, but its strongest winds were offshore, and in a relatively small area. According to a National Hurricane Center report on the storm, the most intense winds at Hobby Airport during the storm were 81 mph, and at Bush Intercontinental Airport, 78 mph.
Such wind strengths are characteristic of a minimal Category 1 hurricane.
Last direct hit in 1915
Hurricane Carla, in 1961, was a much larger and stronger storm, but it hit farther down the coast, at Port Lavaca, nearly 150 miles southwest of Galveston.
The last Category 4 hurricane to directly hit Galveston did so nearly a century ago, in 1915, when the city's population was about 100,000.
So it's possible, but it's been awhile.
After Allison, the Houston region took great strides in widening its bayous and hardening critical areas, such as the Texas Medical Center, against floods. After Ike, the region, under the guidance of engineers such as Rice's Phil Bedient, is studying options to mitigate flooding from Galveston Bay that pushes into the Clear Lake and Ship Channel areas.
When asked what he was aware of being done to address the windstorm threat, Bedient paused a moment.
Then, he said, "You raise a good question."