We see the images from Houston, and they're shocking. Houston is a city under siege from a flood that feels biblical in scope and beyond devastating in the toll it's taking on life and property.
The question many in North Texas are asking is, can it happen here? And the answer, most assuredly, is yes.
The only thing standing between downtown Dallas and 40 feet of standing water — a disaster of Houston-like proportions — is a pair of 90-year-old earthen levees.
But that pertains only to the Trinity River, which has flooded numerous times in the past, albeit without ruptured levees, which besieged New Orleans in the wake of Hurricane Katrina in 2005.
As with Houston, Dallas harbors a second concern that experts contend could be even worse.
In the rush from wilderness to pavement, cities have squandered grasslands and wetlands that in decades past would have captured and sucked up rainwater like a sponge. In their place are miles and miles of interlocking concrete that have the effect of accelerating the flow of rainfall and keeping it trapped.
Barbara Minsker, chair of the Civil and Environmental Engineering department at Southern Methodist University, cites also the "urban heat island problem," which she says is "smacking Dallas and getting worse and worse."
She cites a recent report by the Texas Trees Foundation, which found that "the city of Dallas is up to 15 degrees hotter than the surrounding countryside because we have so much pavement."
Concrete has the effect of catching the sun "and reflecting it back out," Minsker says.
The SMU professor spent 20 years teaching in Illinois, which, like Texas, is hot during the summer.
"But it doesn't cool down at night here," she says. "The pavement keeps radiating the heat back out. That same pavement is what causes flooding problems."
Dallas is not unique to this, but, Minsker says, "I've really been struck by how much flooding I've seen here in the wake of major thunderstorms."
Therefore, it's only natural to wonder if Dallas could fall prey to the Noah-like flood permeating Houston, whose Harvey-related rain totals now exceed 50 inches.
Despite believing that Dallas is unlikely to suffer the effects of a hurricane as severe as Harvey, Minsker says the area has weathered "severe storms in the past that caused flood-related deaths." Those, she says, are predicted to become more common under climate change.
"I think we are very vulnerable," Minsker says. "One of the things we're trying to do is to advocate for more green spaces that will soak up the water and more permeable pavements that will transmit the water to the soil underneath."
In short, she says, "The more we build and build and build and build, the worse this problem gets."
There are, Minsker says, two kinds of floods — river floods, a la the Trinity, and flash floods. The latter happen when rain falls so fast "that the stormwater drainage system can't keep up with it. And so, flash floods happen throughout the region."
Even now, the figures are daunting.
Between 2011 and 2016, the state of Texas recorded the second-highest number of flood-related fatalities in the nation, according to the National Weather Service. In addition, it recorded the third-highest number of flood-related injuries and the second-highest flood-related figure related to monetary damage among all U.S. states.
The North Texas region alone had the highest number of flood-related fatalities in Texas.
For that reason, says the SMU professor, flash flooding and its growing severity — made worse by residential and commercial development and, yes, climate change — poses a greater concern for North Texas than breaches of the Trinity levees.
The problem with any levee system is, she says, that they're built to a certain capacity.
The flow capacity of the Trinity River levee system in Dallas is 277,000 cubic feet per second, according to Clay Church, a spokesman for the U.S. Army Corps of Engineers.
Has that ever been exceeded?
No, he says, not since the levee system underwent what he calls "a major rebuild" in the late 1950s and early 1960s, after its creation in the aftermath of World War I in the 1920s.
Is the corps confident that the levee system, as it exists today, will keep floodwaters below its capacity?
"Well," Church said, "Mother Nature has the last call on that."
Houston, now the epicenter of what is being called the most extreme rain event in U.S. history, has a chance to alter the paradigm for decades to come.
And yet, Church is confident that Dallas-Fort Worth can fend off a similar calamity.
"The six reservoirs and the two major floodway systems, those are designed according to what we call the 'maximum probable storm,'" Church says. "The maximum probable storm is what produces the maximum probable flood."
As it stands, "the system is designed to handle that." It has in the past — at least, so far.
Nick Fang, an assistant professor in the civil engineering department at the University of Texas at Arlington, says Harvey is utterly unprecedented, "a one-in-every-800-years event," and for that reason, it may not offer the fairest comparison.
After the 21st century hurricanes Rita and Katrina, both of which occurred in 2005, the U.S. Army Corps of Engineers undertook an extensive examination of its levee systems.
"And then you also have the factor," Fang says, "that the Dallas-Fort Worth area is very different from Houston. We have so many more reservoirs," which hold and release water as needed.
"During a big event such as this, area reservoirs will hold water, thus serving as flood-control facilities," Fang says. "That helps by offering a lot of additional protection."
Even so, Fang agrees with Minsker about development.
"More and more of it," he says, "introduces a higher degree of imperviousness, and that greatly increases runoff."
Fang notes, however, that local and regional detention ponds provide additional storage of floodwater. For that reason, he says, more such ponds are needed.
Dallas fell prey to a major flood in May 1995, when 15 people were killed and more than 100 injured by a storm that carried softball-sized hail, pelting rain and winds in excess of 70 mph.
The emergency room at Baylor University Medical Center flooded. The parking lot at Fair Park Music Hall flooded, stacking cars on top of each other during a Dallas Summer Musicals performance.
Dozens of Deep Ellum businesses sustained devastating losses, with some fending off invading water that rose as high as six feet indoors. Casualties included computer and phone systems and millions of dollars in company inventories.
And that was just one occurrence.
"If you get a large-enough storm that causes the levees to reach their capacity, or you get several storms in a row, you start to get a whole lot of water, and yes," Minsker says, "that could happen in Dallas."
Therein lies the apocalyptic specter of a Houston-like crisis: You might incur twin calamities, with levees reaching their capacity and overflowing, coupled with flash flooding on such a torrential level that infrastructure can handle neither.
So how safe is the Trinity River levee system?
Mayor Mike Rawlings calls the system "pretty much impenetrable. We have hired expert upon expert upon expert for regular inspections to make sure the levees would not be breached in some fashion. The size of them is significant. The height of them is significant."
The Army Corps of Engineers regulates the system, "and they are saying currently," Rawlings says, "that it's providing flood protection for 1,500 to 2,500 years. Could one of those come along? Potentially. But what was built years ago and added to and intensified in the last 20 years — we have done a lot of work since Katrina — makes us feel great about the levee system."
Church, the Army Corps of Engineers spokesman, says the system worked during floods in 2016 and 2015, when Dallas incurred "historic rain totals, and the system worked as designed. The system continues to work as designed."
He calls it, however, "a risk-management system. So, it doesn't eliminate all risk, but it does provide mitigation from flood damage."
The Trinity River levee system was installed before the Great Depression and, in the words of the Army Corps of Engineers, "strengthened and improved" after World War II.
"Infrastructure in our country overall is not in the best of health," Church says. "The dams and levees we operate in the district office, we continue to assure that they are maintained to the best standards we know of."
But, as Church says with a sigh, "Old is a relative term."