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IPFS News Link • Natural Disasters

No One Is Ready for the Next Katrina

• Wired

After the storm, after the flooding, after the investigations, the US came to realize that 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. In that way, what happened was all but inevitable.

And just as the storm is not to blame, New Orleans is not unique in its vulnerability. The city endured a lot of tsk-tsking in the aftermath of Katrina, as if the storm was the climax to a parable about poor urban planning. Sure, the city sits below sea level, at the end of hurricane alley, and relies heavily on an elaborate (and delicate) system of infrastructure. But where the city's geography is unique, its vulnerability is anything but. Just about every coastal city, state, or region is sitting on a similar confluence of catastrophic conditions. The seas are rising, a storm is coming, and critical infrastructure is dangerously exposed.

The basic math of carbon dioxide is pretty simple: Generally, as CO2 levels rise, the air will warm. Warmer air melts glaciers, which drip into the sea—even as the water itself warms, too. Both cause the oceans to rise. Even if the entire planet stopped emitting carbon dioxide, Earth would continue to suffer the effects of past emissions. "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.

The passive threat of infrastructure

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.


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