Climate Change Worsens Coastal Flooding From High Tides Flooding from extreme tidal swings was once just a rare nuisance for coastal cities. But rising sea levels have increased the frequency of these nuisance floods as much as tenfold since the 1960s.

Climate Change Worsens Coastal Flooding From High Tides

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A wave of high tides is expected to hit much of the East Coast this week. These special tides occur a few times a year when the moon's orbit brings it close to the earth. But scientists say that lately even normal tides throughout the year are pushing water higher up onto land. As NPR's Christopher Joyce reports, that is causing headaches for people who live along coastlines.

CHRISTOPHER JOYCE, BYLINE: The tides, as Bob Dylan might've put it, they are a changin'. High tides around the East and Gulf coasts are getting higher, to the point where regular high tides are beginning to look more like the rare so-called king tides hitting the East Coast this week. Ocean scientists say tides are higher because sea levels are higher. The result is a growing epidemic of small floods in coastal communities.

WILLIAM SWEET: What we have found is that nuisance flooding has substantially increased in frequency.

JOYCE: William Sweet is an oceanographer at the National Oceanic and Atmospheric Administration, and substantially increased means a lot.

SWEET: We had areas that were increasing by a factor of nine over the last 50 years.

JOYCE: Nine times as many nuisance floods from high tides in some places. NOAA scientists say that follows from the fact that because of climate change, oceans, on average, are eight inches higher than a century ago. And, Sweet says...

SWEET: It's going to get worse. Sea level rise is expected to accelerate during the next century as the oceans continue to warm and expand and the ice shelves lose mass as the water melts into the ocean.

JOYCE: NOAA's conclusions come from a century of data collected by tide gauges placed along coastlines. The same data are the basis of a study out this week from an environmental group, the Union of Concerned Scientists, called "Encroaching Tides." The report forecasts what higher tides could mean for 52 communities from Maine to Texas. Climate scientist Melanie Fitzpatrick is one of the authors.

MELANIE FITZPATRICK: Certainly communities that are unfamiliar with flood conditions will start to see that flooding regularly. And our projections show that in the next 15 years, two-thirds of the communities we looked at could see a tripling or more in the number of high tide flood events.

JOYCE: This includes cities like Boston, D.C., Charleston and Miami. Fitzpatrick says communities have three options.

FITZPATRICK: Firstly is living with it. Secondly is actually moving back, retreating. And then the third way of addressing it is to fortify or defend.

JOYCE: The city of Annapolis in Maryland is doing all three. Annapolis sits at the mouth of the Severn River on the Chesapeake Bay. Founded in 1649, it was a colonial port. Life still revolves around the city dock. Workers today are preparing for the nation's largest sailboat show. Historic buildings from the 18th century surround the dock.

LISA CRAIG: Our historic district is the economic core.

JOYCE: Lisa Craig runs the city's historic preservation division.

CRAIG: Look, we're standing here looking straight up at the state house dome. It's a capital city. I mean, this is an iconic, historic community.

JOYCE: And these buildings are now threatened by freakish high tides. In fact, nuisance floods here have increased from four a year in the 1950s to 40 a year now. Craig says people have learned to live with it.

CRAIG: I walk down to the yacht club at 11:45 to go to lunch, and I anticipate on some high tide days that I'm not going to be able to walk back. I'm going to have to take the long way around.

JOYCE: But the city is fortifying itself as well. New flood maps identify buildings in jeopardy. There's a tax break for owners who prepare for flooding. That could mean simply building a barrier across a door sill or windows, or something more robust.

CRAIG: Some businesses may want to increase the height of the interior of a property and create a step up or two steps up if that's the case, or a ramp.

JOYCE: Holding back water has now become business as usual in downtown Annapolis. And if sea level keeps rising, it will be in a lot of other places as well. Christopher Joyce, NPR News.

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