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U.S. Cities Struggle To Meet Tighter Flood Standards

What Harvey revealed for us is that our flood defenses will eventually be overrun.

The recent string of Hurricanes — Harvey, Irma and Maria — has sparked calls for more flood protection. In fact, after Hurricane Katrina twelve years ago, federal officials did tighten standards, but it turns out many flood-prone communities are still struggling to meet them.

Neighborhoods like fast-growing Natomas, in northwestern Sacramento.

"In the past month, I've probably helped six families move up from the Bay Area,"says realtor Cynthia Hextell. She's standing outside a recent sale: a tidy two-story near a good school that sold for well over asking price.

Are buyers ever nervous about the flood risk? "Never," says Hextell. "I have never had that come up."

But the risk is real.

Sacramento doesn't have hurricanes to worry about. Instead, it's the huge winter storms that hit the Sierra Nevada. The city was built at the confluence of the Sacramento and American Rivers, which drain an area the size of West Virginia. More than a century ago, it used to become an inland sea during really wet years.

Now Natomas is ringed by 42 miles of dirt, earthen levees designed to keep a major river from flowing around its low-lying homes. But they are old, and not in great shape.

"During a flood event, the flood depth would be ten to twenty-five feet," says Jim McDonald, a principal planner for the City of Sacramento. "We realized a lot of the city didn't have 100-year flood protection once we took another look at our levees."

"It's Pretty Scary When You Think About It"

After Hurricane Katrina, federal flood planners tightened up the standards for levees to make them safer. That meant Natomas was no longer up to par.

Federal rules require 100-year flood protection, which is a storm that has a 1-in-100 chance of happening every year, or a 26 percent chance cumulatively over a 30-year mortgage.

Natomas was only rated for a 33-year storm.

The risk is so great that in 2008, federal officials mandated a building moratorium: no permits for new construction until the city worked on its levees.

"It's pretty scary when you think about it," says Rick Johnson, director of the Sacramento Area Flood Control Agency. "We have over a hundred thousand people living out there."

New Orleans used to top the list of American cities most at risk from river flooding, but it's been replaced by Sacramento.

"They've rebuilt New Orleans to the point where their level of protection is higher that ours right now," Johnson says.

Protecting all of Sacramento will cost $4.4 billion and take nearly a decade more, with $1 billion to spend in Natomas alone. But money from Congress has been slow, and there is intense competition for those dollars. Sacramento has to fight for its share every year.

The city decided to go ahead with construction even before any federal funds came in, using state money and taxing local residents. So far, Natomas has completed about 18 miles of levee improvements. In 2015, the federal government declared that enough work had been done to lift the building moratorium.

A Perverse Incentive To Build

"The federal government has become an unreliable partner," says Jeffrey Mount, a flood expert at the Public Policy Institute of California.

He says more communities are starting to tax themselves to pay for flood improvements, but that creates a bizarre incentive to put more buildings and people in risky areas.

"Do they stop growing?" he says. "Well, if they stop growing, you can't pay for new infrastructure."

Mount says Sacramento is doing something right: elected leaders have stayed focused on the problem and the city is aiming for 250-to-300-year storm protection, higher than the federal standard, or the state one. After Katrina, California required urban areas to have 200-year storm protection.

"But here's the fundamental problem," Mount says. "What Harvey revealed for us is that our flood defenses will be eventually be overrun."

Hurricane Harvey was a 1,000-year storm, at least, and with a warming climate, storms could become more intense. Mount says when it comes to floods, many communities are left simply hoping they get lucky.

Copyright 2017 KQED

Lauren Sommer covers climate change for NPR's Science Desk, from the scientists on the front lines of documenting the warming climate to the way those changes are reshaping communities and ecosystems around the world.