A home is surrounded by floodwaters from Hurricane Ike in Galveston, Texas September 13, 2008.
A home is surrounded by floodwaters from Hurricane Ike in Galveston, Texas September 13, 2008. David J. Phillip/Reuters

As the heavily developed Houston area braces for Hurricane Harvey, an urban flooding expert sees a catastrophe in the making.

Hurricane Harvey is about to slam into Texas this weekend as a Category 4 storm, the first of this magnitude to make landfall in the U.S. in 12 years. Some forecasts are calling for a staggering 40 or more inches of rain, with storm surges cresting between six and 12 feet. In anticipation of the deluge, Texas Governor Greg Abbott declared a preemptive state of emergency and issued orders of evacuation spanning 30 counties. As the storm churns toward land, its precise path—and the destruction its 120-mph winds will leave behind—is somewhat uncertain. But by nearly all accounts, the situation is going to be dire.

The degree to which storms become “disasters” is determined, at least in part, by factors beyond wind speeds or rainfall numbers, as Laura Bliss pointed out in 2016. One major contributor is “how many people and buildings are in the wrong place at the wrong time.” On this front, the situation in Houston could hardly be worse.

As the population has boomed across this Sunbelt city in recent years, an increasing number of people and buildings find themselves in a vulnerable position. Meanwhile, thousands of acres of wetlands that might have helped absorb excess rainfall have been gobbled up by development. When paved surfaces can’t perform the crucial work of stormwater retention, “even lesser storms are invested with more destructive power,” Kriston Capps noted last summer. Harvey is no minor storm—and it is slated to batter a city with relatively poor flood infrastructure and no statewide insurance requirement.

Just how bad will this be? CityLab spoke with Samuel David Brody, director of the Center for Texas Beaches and Shores at Texas A&M Galveston, to find out.

Some meteorologists have sounded blazing alarms about the forecast’s combination of rainfall, wind, and inland flooding. Based on your research, why is this confluence of factors especially threatening?

The storm right now is reminiscent of a storm of 2001 called Tropical Storm Allison. It hit the coast and stalled out and dumped ridiculous amounts of rainfall in the Houston area. So this storm is going to be a surge event down south, with wind and rising seawater, but then a ginormous rain event to the northeast in the Houston area.

How many people lived in Houston in 2001 compared to now? There’s been a 23 percent population increase. There’s been miles and miles of new pavement and structures put in harm’s way. Allison was one of the most devastating storms of all time in the United States. This is going to be much worse, if something with that much rainfall sits over Houston for a couple of days.

This storm has it all. It’s got surge and winds, but for the Houston area, right now the biggest threat is the rainfall. The economic impact and loss of property and human lives could be significant.

In addition to evacuating, what other steps can people take right now to keep themselves and their property safe?

One of the unsung heroes of flood risk reduction techniques is drainage maintenance. It’s not sexy, and it never gets in the news, but I drive around all these neighborhoods in Houston and I see clogged street drains. So when the rains come and they’re filled with trash and debris, it’s like they're not even there. They can’t operate. And then you got a lot of street and home flooding that way. Make sure your drains in the street and on your property are working. Move your valuable contents to the second floor or an attic, if you have one.

Much of your research focuses on urban flooding. How do those conditions differ from a water-related deluge in non-urban areas? Why is the Houston-Galveston area so susceptible to flooding and other water hazards?

The 100-year flood plain is almost nonsense in places like Houston. When we look at insured losses over time, almost half of them are outside the 100-year flood plain. That marker of risk really isn’t capturing reality, because we’ve so altered the natural drainage patterns over time through built environment interventions. That shows up more easily in Houston. It’s so flat, you sneeze and the floodplain changes.

Houston has a large amount of pavement—impervious surface—put down in a very low-lying, flat area that experiences heavy rainfall events. I tell my students that the problem is complicated; there are lots of underlying factors. There are physical conditions. There's environmental change increasing these heavy rainfall events. There’s sea level rise and changing temperatures. All of those are small, slow-moving gears as part of this overall problem. The bigger gear moving much faster is human development—the built environment. Houston added 100,000 people last year alone. That set us up for this potential catastrophe.

Last year, ProPublica reported that development has claimed 75 percent of flood-absorbing land in the Katy Prairie area, which helped manage stormwater. What’s the effect of building on or paving over these types of areas?

I think it’s a combination of lots of different factors, [including] developing the Katy Prairie area, particularly converting those wetlands that store, hold, and slowly release storm water. This is an important part of the problem. It’s the lack of smart development and spatially targeted development that looks at the system—the watershed and the drainage patterns over a large region, not just a specific parcel or set of parcels that will realize short-term economic gain. Over the long term, this creates a drainage pattern that causes homes to be lost and people to die.

In my mind, the story isn’t so much climate change and environmental change—which is real and important. It’s more about the way we've constructed our urban fabric without thinking about building codes and regional development in a systematic way. [This] makes Houston more susceptible to this type of event than any other city in the country.

You talked about a population growth and building boom. Once those are done deals, what other moves does the city have? Can you walk back some of these effects?

[Those tactics] generally fall into two broad areas. One is resistance: floodwalls, flood-proofing homes, neighborhood gates and levees, household doors and windows that that hold back the water. And then there’s avoidance, which can also be retroactive, such as elevating structures so that you’re letting the water flow under the buildings.

Houston has a one-foot freeboard requirement for new homes, and that means that [in] new homes, the first floor has to be a foot above the 100-year level of inundation. I don’t think that’s enough. In fact, no one I talk to thinks that’s enough; at least two feet is kind of the gold standard. But you can go into an existing home and elevate it.

Or avoidance can be retroactive in terms of removing a structure out of harm’s way. That’s buying a home or property and converting it to park land or open space. I was surprised to learn in my research that the number-one place for flood buyouts in the country is Houston. Over 3,000 parcels have been bought out in Houston alone to remove them from flood zones. That was largely in response to Tropical Storm Allison in 2001, when there was money to do it.

Last year, Houston installed its first “flood czar,” Stephen Costello. Is the city more prepared this time around than it was for previous storms?

If you’d asked me two months ago I’d say no, but now I'm going to say yes. [Costello] was given no resources and an intractable problem. But he’s evolved to the point where he now has this drainage program, Sweep the Street program, [and] he’s understanding the complexity of these problems. It's not just big engineering projects, but it’s community awareness and local activities. I think he is making a difference and would do more if he had more resources and time and a broader mission to address the problem.

Stuff is being done. More retention is being put in. There’s a lot of talk about expanding the stormwater management system. But this is not easy; quick-fix solutions and technology and structures alone aren’t going to solve the problem.

How do you incentivize people to think about future threats when there aren’t storms in the immediate forecast?

It's genuinely integrating these issues into kind of the residence structure in daily life—for example, through homeowners associations. If we’re really going to educate people and change their behavior, homeowners associations are powerful. Maybe that’s an intervention point. Rather than have billboards or hisregional messaging, work with homeowners' associations to get the message out way before any storm.

Also, even before they decide to locate in an area, [prospective homeowners should be able to be] aware of the risk. We just released this website we called Buyers B-Where. It’s kind of taking the Zillow philosophy, and you can click on a parcel, put in an address, and it’ll give you a score for a range of risks—not just flooding, but also technological risks like how far you are from a contaminated site or toxic release site.

Let’s assume density doesn’t decline. Looking forward, at the policy level, how can this part of Texas area become more resilient?

This is inherently a human problem—and in some cases a social [and] economic problem, where you have a lot of low-income minority communities that are disproportionately impacted by flood events. There are social justice issues here that need to be baked in to any larger-scale flood-risk reduction solution. It’s not just a bigger pipe or a bigger detention pond to hold more water—it’s much more complex.

Part of the solution is regional thinking. If we don’t think regionally, we’re going to come up with the wrong solutions. Harris County needs to think and act and collaborate more with surrounding counties like Fort Bend County and counties to the west. Jurisdictional boundaries don’t adhere to the watershed-based boundaries, and that’s problematic, because the decision-making and activities are fragmented across these larger natural landscapes. What happens in Katy to the west is going to impact the medical center way to the east. Understanding that and building decision-making collaborative partnerships around those regional landscapes is the only way to really address the problem, particularly in low-lying areas like Houston.

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