After the storm, after the flooding, after the investigations, the US realized what happened to New Orleans on August 29, 2005 was not a natural disaster. The levee system built by the US Army Corps of Engineers had structural flaws, and those flaws were awaiting the right circumstances.
New Orleans is not unique in its vulnerability. The city endured a lot of scolding in the aftermath of Katrina, as if the storm was the penalty for poor urban planning.
Many coastal cities and regions could face a similar confluence of catastrophic conditions. The seas are rising, a storm is coming, and critical infrastructure is vulnerable.
“We’ve got at least 30 years of inertia in terms of sea level rise,” says Trevor Houser, a Rhodium Group economist who studies climate risk. And even if the sea weren’t rising, the rate of urban growth will more than double the area of urban land at high flood risk, according to a study Global Environmental Change published earlier this year.
But the sea is rising, at about .13 of an inch per year, for the past 20 years. (It was rising before then, too, but at about half the rate for the preceding 80 years.) Another recent study calculated that the world should expect about 4 feet of sea level rise for every degree Fahrenheit the global average temperature rises. This puts nearly every coastal city, in every coastal state, in danger of floods. Climate Central has an extensive project looking at sea level risk, if you’re curious about your city’s risk.
Warm air also holds more moisture, and moisture holds more energy, hence stronger (though not necessarily more frequent) storms. Those storms combine with high sea levels to create a danger greater than the sum of their parts. In a combined flooding event, a severe storm traps a city between rainfall and surging seas. Higher sea levels cause rivers to back up, water tables to saturate, shorelines to shorten. Storms—which are likely to be stronger than before—have fewer options to run off, so they pool and flood. And America built its coastal civilization oblivious to their threat.
Take Florida, the most climate-threatened swath of American soil. It’s low, flat, built on porous limestone, and hurricane prone. According to a new analysis by disaster insurance agency Karen Clark and Co., Florida has four of the 10 US cities most vulnerable to combined flooding events.
Florida, knowing its place in the world, has copious levees and seawalls. But the levees are there mostly to protect against the Everglades. The seawalls are about as good at breaking a hurricane as a hood ornament is at breaking the wind. And all of that infrastructure is of little use in the face of combined flooding events—the sea will simply come up from below. Miami flooded last year when the storm sewers backed up because the water table was too high to drain them.
The Sunshine State’s geography makes it an easy target for blame (not to mention hurricanes). But if there’s anything the US should have learned in the decade since Katrina, it’s that storms don’t always hit where you expect them—because, you know, Sandy. “Florida is definitely the most vulnerable place, but you also have places like Norfolk that are built on the coastal floodplain, and parts of New England where there is a lot of sunk infrastructure very close to the increasingly vulnerable coast,” says Houser. The pattern repeats itself all along the Atlantic coastal plain: Physical protections are largely insufficient to protect against a new class of climate threats.
And then, sometimes, that infrastructure falls apart entirely. Louisiana’s levees couldn’t have held off Katrina entirely, but it was their collapse, not the hurricane itself, that turned the Big Easy into a bathtub. “Some were improperly designed, some were improperly constructed, the rest were improperly maintained,” says Sandy Rosenthal, the director of Levees.org, an infrastructure watchdog group.
That same sentence could apply to key infrastructure nationwide. A lot of the country’s infrastructure—its bridges, transportation corridors, airports, seaports, water supply systems, electrical grids, flood control, and so one—were built poorly, hastily, or both. A lot of it is old and neglected. In a 2013 survey, the American Society of Civil Engineers gave US infrastructure a D+ grade.
“A lot of infrastructure went up in the midcentury,” says Solomon Hsiang, a UC Berkeley economist who studies public policy. “Now we’re reaching the end of the natural lifetime of that infrastructure, and we need to decide that we can no longer ride on all the investment that occurred 50 or 60 years ago.” Much of this stuff is directly vulnerable to climate change. Earlier this year, the Army Corps of Engineers released two surveys describing hundreds of dams and thousands of levees vulnerable to rising seas and stronger storms. Threats identified—but not yet remedied.