Mapping Coastal Flood Risk Lags Behind Sea Level Rise
Sea levels are rising and climate scientists blame global warming. They predict that higher seas will cause more coastal flooding through this century and beyond, even in places that have normally been high and dry.
But mapping where future floods will strike has barely begun.
The Federal Emergency Management Agency maps where people are at moderate or high risk of flooding. Most people with property in hazardous areas — where the annual risk of a flood is one in a hundred or more — are required by law to buy federal flood insurance from FEMA's National Flood Insurance Program.
But FEMA's insurance maps are based on past patterns of flooding. Future sea level rise — which is expected to create new, bigger flood zones — is not factored in.
So some communities are doing the mapping themselves. Like Annapolis, the state capital of Maryland.
About 40 times a year, the Chesapeake Bay floods this port city, where Lisa Craig is chief of historic preservation. As she and I walk downtown near the city dock on a sunny summer day, we soon encounter sheets of water on the street.
"You can see we're not quite at high tide and we've already topped," she says. This overflow onto the streets wasn't caused by a storm.
"This is just a normal high tide," Craig says.
Flooding is now "normal" in Annapolis. So construction crews are installing metal flood gates in doorways, and vents in floors to drain floodwater from buildings that were built centuries ago, when this area was usually high and dry.
Such measures are fine for this kind of "sunny day" flooding. But Michael Dowling, an architect who works on flood protection in Annapolis, says a big storm will push water higher as sea level rises.
"That's the thing to remember," he says. "Sea level rise is one thing. As our mean water level goes up, if you put a storm on top of that you're going to have a different situation."
By "different situation" he means new flood zones. But where exactly will they be when sea level rises?
City planners in Annapolis asked the Army Corps of Engineers to show them how the flood zone would expand if sea level here rises 3.7 feet — a midrange prediction for 2100. They found that a flood from a one-in-a-hundred year flood would be almost twice as high as it would be if such a storm hit now.
It would be 8.2 feet high – "about the top of that piling," Dowling says, pointing to a wooden piling that rises well above our heads near the water's edge. Where we're standing would be well underwater. And so would a big part of downtown — parts of Annapolis that have never flooded before.
Craig says she wants property owners here to think more about that future. "I think it's going to come down to when the property owner is required to make some changes, they will," she says, adding that "we'll have to incentivize, encourage" people to do that. Because right now they don't have to buy flood insurance — they're not in FEMA's current flood hazard zone.
And getting property owners to buy in to that idea won't be easy.
"Ninety percent of the people that have called me over the past 20 years want to get out of paying for flood insurance," says David Guignet. He's a floodplain engineer for the state of Maryland and coordinates the state's participation in FEMA's flood insurance program.
Given how hard it is to get people to buy flood insurance now, he says, Maryland isn't about to require insurance for people who may end up in future flood zones.
But Guignet does want people to know if their property lies in the path of sea level rise. He says a homeowner may look at his or her property on a map and decide, " 'In 30 years, if the sea level rise is going to get to that point, well then I might decide that I want to move by then,' " he says, " 'or maybe do other things when I modify my house so the next [addition] I build is higher.' "
On a computer screen in Guignet's Baltimore office, we look at a map of Oxford, Md. Lots of coastal properties there lie in FEMA's flood zone. Guignet clicks an icon to add 3 to 5 feet of sea level rise. Most of those properties on the map are suddenly covered in blue: permanently submerged. And that's calm water; a big storm would push water even farther inland.
And if sea level rises more than 5 feet? The screen shows what happens.
"Now it looks like Oxford is gone when you have the 5- to 10-foot level on top," Guignet says.
Five to 10 feet of sea level rise isn't likely, but Guignet says homeowners should be able to see the full range of risk scenarios that scientists are applying to coastlines.
FEMA isn't making maps like these, although Guignet says they helped Maryland with the data and technical support do it. In fact, the agency is still struggling to update its existing flood maps.
Roy Wright, FEMA's flood insurance chief, told a Senate hearing recently that almost half its maps are "credible," but not "precise." Precision, Wright said, "comes down to how much we can afford to buy. It's a resource question. Precision costs more money."
Last year, FEMA got $311 million to spend on mapping, about three quarters of what the agency said it needed. President Trump's new budget would cut the mapping budget even more.
This comes years after independent flood experts – FEMA's Technical Mapping Advisory Council — told the agency to start paying more attention to sea level rise.
What does FEMA need to fix its existing maps and start factoring in future risks from climate change?
"I must have elevation data that is digital to do any of the [mapping] products," Roy Wright tells me, "including the future risk pieces that you're mentioning."
Elevation data show how high buildings and land are above sea level. The best data come from airborne lasers, called LIDAR, and the technology is expensive. Wright says so far he only has precise elevations for half the country.
While maps that FEMA uses to decide who must buy insurance don't include sea level rise, the agency is advising local governments on where it might be risky to build in the future, and encouraging them to build "stronger and higher." But Wright says it's not FEMA's job to require people to insure themselves against future risk.
"Communities have the option to include future risk on their maps," he says. "It's their choice."
FEMA's role, Wright adds, is to inform people of their risks. And the agency isn't yet communicating true flood risk to the public the way he'd like to, he says.
"It hasn't worked effectively enough yet," he says. "I think that's one of the public policy challenges. What will the reality be for that homeowner 10 years down the road, 20 years down the road?"
Meanwhile, scientists say the rate of sea level rise is accelerating.
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