It's not news to people living in Texas, but for many Americans, the epic floods striking the state this week highlight how intensely the skies can open up there.
"We can get three, four, five inches in a span of an hour or two," says Philip Bedient, a hydrologist at Rice University in Houston. That rate makes parts of the Lone Star State ground zero for some of the most intense bursts of rainfall in the United States.
Such rates, along with projections for population growth, point to a need to inject fresh energy into efforts that communities already have made to ease their vulnerability to floods, natural-hazard specialists say. Throw global warming into the mix, and events delivering the heaviest rainfall could increase by 10 to 20 percent for much of Texas, according to last year's National Climate Assessment, overseen by the US Global Change Research Program.
Progress in reducing vulnerability to floods is evident in many places around the state, notes Walter Peacock, director of the Hazard Reduction and Recovery Center at Texas A&M University in College Station. Cities are curbing development along waterways, while areas outside city limits are increasingly taking steps, especially in terms of building codes.
"Positive things are happening," he says. "They just are not happening as quickly as many would like."
The pace, Dr. Peacock and others say, is dictated more by politics and budgets than by a dearth of ideas about how to reduce vulnerability to flooding.
Between 2000 and 2030, Texas' population will have grown by nearly 12.5 million people, according to US Census Bureau projections. That translates into the fourth fastest growth rate after Nevada, Arizona, and Florida.
Much of that growth is expected to take place in some of the state's most flood-prone areas: Houston, the corridor from Austin to San Antonio, and the Rio Grande Valley around Brownsville, Peacock notes.
"Two of those three are experiencing major floods right now," he notes.
"We really do need to think about continuing to develop the way we have been developing – that is, sprawling cities, lots of concrete, lots of blacktop," he says. "We're putting in so much impervious surface that water runoff becomes one of the major problems we have to address."
Indeed, for the past 15 years, new housing developments generally have had to include runoff ponds or other forms of catchment basins whose capture and gradual release of water matches the discharge that would have occurred in the absence of development, says Dr. Bedient of Rice. But that still leaves housing in older, low-lying areas vulnerable to repeat flooding.
Along bayous and creeks that run through metropolitan areas, counties, communities, and citizen groups have worked together to convert the waterways’ banks into greenways and parks. This prevents development right along the channels.
Communities also have bought property in the most vulnerable areas to help expand the amount of land that floodwaters must cross to reach homes or businesses.
But much of the progress so far has been taking place in cities, specialists say. There, officials can use building codes or other forms of regulation.
Unincorporated portions of counties, Peacock says, represent the current frontier for reducing vulnerability to flooding. These are the areas where more concrete and blacktop are being applied and where wetlands – which can provide natural upstream storage during floods – are vulnerable. They are the jurisdictions that must deal with the spillover of development beyond city limits, and they often can run short of the expertise, the money, and, until fairly recently, the legal tools needed.
“They lack the ability to enact land-use planning and land-use codes that people say they want,” Peacock says. For a long time, “counties could not even have a building code in the state of Texas.”
That began to change six years ago, when the Texas Legislature enacted a measure that would allow certain counties to use either the county seat's residential building code or an internationally recognized model code. The change applied to residential projects that began after Sept. 1, 2009.
Harris County, which includes Houston and which some see as one of the more progressive counties in the state, quickly adopted a code after the measure passed.
Flooding from tropical storm Allison in 2001 stimulated efforts to improve flood control, notes Richard Smith, president of the Cypress Creek Flood Control Coalition, a 15-year-old group that has worked with the county to improve flood resilience along Cypress Creek. At 320 square miles, the creek's watershed is the largest in Harris County and it's also where much of the county's development is taking place.
One question involves the use of projections of future climate conditions in addressing drainage needs for new developments. Currently, the drainage needs are based only on today’s conditions. But at the federal level, there have been moves to require that future conditions be factored in to plans.
For the coalition, at issue at the moment is an application for a development whose drainage plan meets the county's current criteria. But the coalition is working with the county in hopes of getting it to apply the "future conditions" criterion to the application. An independent analysis of the developers’ plan indicated that it would lead to more flooding in the future, not less, Mr. Smith says.
For the developers, it's a tough trade-off, he acknowledges.
“It’s going to cost the developers more money because they have to take more land that they would devote to homes and instead use it to expand the detention pond,” he explains.
Overall, communities and counties have a growing range of regulatory tools they could use, or incentives they could offer that don't involve regulations, according to a study that Peacock conducted for the state and for the National Oceanic and Atmospheric Administration in 2011. But these can remain tough sells in a state that is big on small government, he adds.
Challenges also arise with higher levels of government, notes Bedient. He points to a project involving Brays Bayou, which runs through southwest Houston and into another bayou that empties into the Houston Ship Channel.
The project is part of a large flood-control effort that grew out of serious flooding from tropical storm Allison in 2001. The Brays Bayou project was supposed to have been finished last year. In the current flooding, work to date has saved some 1,000 structures, according to the head of the Harris County Flood Control District, quoted in the Houston Chronicle.
But delays, which Bedient attributes to slow funding from Congress, have pushed the finish date off to sometime after 2020.
The potential cost in flood control? "We would have seen flood levels two to three to four feet lower than what we saw from this flood, which is a lot in this part of the world."