Climate Change Worsens Coastal Flooding From High Tides

Enlarge this image toggle caption Joe Raedle/Getty Images Joe Raedle/Getty Images

A wave of high tides is expected to hit much of the East Coast this week. These special tides — king 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. And that's causing headaches for people who live along coastlines.

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.

As Bob Dylan might have put it, the tides, 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 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.

"What we have found," says oceanographer William Sweet, "is that nuisance flooding has substantially increased in frequency." Sweet is with the National Ocean Service of the National Oceanic and Atmospheric Administration, and when he says "substantially increased," he means a lot. "We had areas that were increasing by a factor of 9 over the past 50 years," he says. That's nine times as many nuisance floods from high tides in some places.

NOAA scientists say the big increase is the result of shifts in climate — oceans are, on average, 8 inches higher than a century ago. And, Sweet says, it's going to get worse.

"Sea level rise is expected to accelerate during the next century," he says, "as the oceans continue to warm and expand, and the ice shelves lose mass as the water melts and enters into the ocean."

NOAA's conclusions on rising tides 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.

"Certainly communities that are unfamiliar with flood conditions will start to see that flooding regularly," says Melanie Fitzpatrick, a climate scientist and one of the study's authors. "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."

This includes cities like Boston; New Haven, Conn.; Washington, D.C.; Charleston, S.C.; and Miami. Fitzpatrick says communities have three options: "First, is living with it. Secondly, is actually moving back — retreating. And the third way to address it is to fortify and defend."

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. "Our historic district is the economic core," says Lisa Craig, who runs the city's historic preservation division. She directs my attention to the tower of the statehouse, built in the 18th century.

"Look, we're standing here looking straight up at the statehouse dome," Craig says. "It's the capital city — I mean this is an iconic, historic community." And many of the city's buildings are now threatened by freakish high tides.

In fact, nuisance floods here have increased from about four each year in the 1950s to nearly 40 per year now. Annapolis leads the country in the increase in nuisance flooding recorded by NOAA — a nearly tenfold increase since the 1950s.

Craig says people have learned to live with it. "I walk down to the yacht club at 11:45 to go to lunch," she says. "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."

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

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

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