Up until 2017, Hurricane Katrina was the most expensive natural disaster in U.S. history. After the storm devastated New Orleans in 2005, the federal government spent $120.5 billion to help the city and other affected areas recover (roughly $150 billion in 2017 dollars). Most of the aid went toward emergency relief, with less than half going towards rebuilding the city. Although many structures like levees and schools have been repaired, more than a million people in the Gulf Coast were displaced.
But a week after Hurricane Harvey made landfall in the Houston area on August 25, 2017, Texas Governor Greg Abbott (R) said that his state may require as much as $180 billion in federal assistance—which means the 2017 hurricane could soon exceed the cost of Katrina.
There are many reasons that Harvey is poised to become the most expensive storm. At over two million, Houston’s population is about four times the size of what New Orleans’ was before the 2005 hurricane, which means there were also a lot more homes in Harvey’s path. Although Harvey’s damage is still being assessed, so far about 40,000 homes have been lost and up to a million cars have been wrecked. In addition, flooded metro stations, prisons, and other public facilities will need repair.
“If Harvey hit 20 years ago, there would’ve been many fewer houses to damage,” says Spencer R. Weart, a science historian with a Ph.D. in Physics and Astrophysics. As coastal regions susceptible to hurricanes become more densely populated, the cost of rebuilding all cities will increase.
Unchecked development to meet Houston’s population boom—up 23 percent in the last 15 years—also helped put homes in danger of flooding. Too much concrete and pavement and not enough exposed soil has made it difficult for excess water to flow back into the ground. In addition, weak zoning laws failed to prevent buildings from going up in places where they shouldn’t. CNN reports that hundreds of structures were damaged because they’d been built in the paths of dams constructed in the 1930s.
Another factor at play, Weart says, is climate change. Statistically, flooding like that in Houston should only occur once in 1,000 years, according to the University of Wisconsin’s Space Science and Engineering Center. But this kind of flooding will become more frequent as climate change exacerbates the severity of rainfall.
The Gulf of Mexico was already 2.7 to 7.2°F hotter than historical averages around the time that Harvey hit, so that helped intensify the rain. “The average amount of moisture that the atmosphere can hold goes up by four percent for one degree [Fahrenheit] increase in temperature,” says Kevin Trenberth, a distinguished senior scientist in the Climate Analysis Section at the National Center for Atmospheric Research.
Some parts of Houston received over 50 inches of rainfall—so much that the National Weather Service had to update the colors it uses on its weather charts to properly account for it. This is far beyond the rainfall experienced during Katrina, which averaged five to 10 inches. It’s also far beyond what most U.S. cities could endure without significant flooding, reports NPR. In fact, The New York Timeswrites that “While Katrina showed a failure to build well, Harvey might come to represent a warning about climate change.”
Still, the flooding caused by intense rainfall in Houston could have been mitigated with infrastructure improvements that help drain water, says Michael Wehner, a senior staff scientist in the Computational Research Division at the Lawrence Berkeley National Laboratory. Houston’s flat landscape makes it difficult for excess water to runoff, and the city knows this because it’s flooded before.
“It’s foolish to ignore this,” he says of the need for preventative measures. “Because generally when you have a disaster, it’s expensive. And there’s going to be more.”
The same week that Congress considered an initial disaster aid package of $7.9 billion for Texas, the National Hurricane Center was monitoring a category five storm named Irma threatening to hit Florida, Puerto Rico, and other Caribbean islands.
As of September 6, 2017, Irma had already destroyed the four “most solid” buildings on the island of Saint Martin, ripped the roof off a police station in Barbuda, disrupted phone and radio communications between islands, and caused massive damage and flooding in the Caribbean (in Barbuda, water swelled at least eight feet above normally dry land). Forecasters warned that the record-breaking, category five storm would have catastrophic effects as it continued its journey—potentially driving the cost of rebuilding up even further.