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Flooding is on the rise along America's coastlines. Scientists blame much of the increase on higher sea levels caused by global warming, and they say the flooding will get worse. But mapping where those future floods will strike has barely begun. NPR's Christopher Joyce reports.
CHRISTOPHER JOYCE, BYLINE: Almost 40 times a year, the Chesapeake Bay floods the port city of Annapolis, Md., where Lisa Craig is chief of historic preservation.
LISA CRAIG: But you can see we're not quite at high tide and we've already topped.
JOYCE: Yeah. It's - we've got water on the street here. And this is just a normal high tide?
CRAIG: This is normal high tide.
JOYCE: Flooding is now normal in Annapolis, so construction crews are installing metal floodgates in doorways and vents in floors to drain floodwater in buildings that were built centuries ago. That's OK for this kind of sunny day flooding. But Michael Dowling, an architect who works on flood protection here, says a big storm would be much worse.
MICHAEL DOWLING: That's the thing to remember. Sea level rise is one thing. As our mean water level goes up, you put a storm on top of that, you're going to have a different situation.
JOYCE: That different situation means new, bigger flood zones. But where will they be when sea level rises? The Federal Emergency Management Agency, FEMA, maps the flood zones. Those are places where your chance of flooding in any year is one in a hundred. Most people with property in a flood zone must buy flood insurance. But FEMA's insurance maps don't account for future sea level rise. Annapolis is one of a few communities that is factoring sea level rise into local flood maps. What city planners found is not pretty. If sea level here rises say, 3.7 feet - a mid-range prediction for 2100 - a flood from a really big storm would be almost twice as high as it would be now, over 8 feet high.
DOWLING: 8.2 would be about the top of that piling.
JOYCE: Yeah. So, we'd be underwater.
JOYCE: And so would a big part of downtown. Lisa Craig says she wants property owners here to think more about that future.
CRAIG: I think it's going to come down to when the property owner is required to make some changes, they will. And we'll have to incentivize, encourage.
JOYCE: Which isn't going to be easy.
DAVID GUIGNET: Ninety percent of the people that have called me over the last 20 years want to get out of paying for flood insurance.
JOYCE: David Guignet is a floodplain engineer for the state of Maryland. He says Maryland isn't about to require insurance for people in future flood zones, but Guignet does want people to know if their property lies in the path of sea level rise.
GUIGNET: In 30 years, if the sea level rise is going to get to that point, well, then I might decide that I want to either move by then or maybe have - do other things when I modify my house so that the next level I build is higher.
JOYCE: 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 three to five feet of sea level rise and most of those properties are now covered in blue - permanently submerged. And if sea level rises more than five feet?
GUIGNET: Looks like Oxford is gone when you have the five- to 10-foot level on top.
JOYCE: Five to 10 feet is not likely, but Guignet says homeowners should be able to see the full range of risk. FEMA isn't making maps like these, although it helps Maryland do it. In fact, the agency is still struggling to update its old flood maps. Roy Wright, FEMA's flood insurance chief, told a Senate hearing recently that almost half its maps are credible but not precise.
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ROY WRIGHT: Precision comes down to how much can we afford to buy. It's a resource question. Precision costs more money.
JOYCE: But last year, FEMA's mapping division got just three quarters of the funds it requested. President Trump's new budget would cut it even more. So I asked Roy Wright, what does FEMA need to fix its existing maps and start factoring in future risks from climate change?
WRIGHT: I must have elevation data that is digital to do any of the products, including the future risk pieces that you're mentioning.
JOYCE: Elevation data show how high buildings and land are above sea level. The best data come from airborne lasers, and it's expensive. Wright says so far he has precise elevations for just half the country. When it comes to future sea level rise, the agency is advising communities in flood zones to build higher and stronger. But Wright says FEMA isn't yet communicating flood risks to the public the way he'd like to.
WRIGHT: It hasn't worked effectively enough yet. 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?
JOYCE: Meanwhile, scientists say the rate of sea level rise is accelerating. Christopher Joyce, NPR News.
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