According to new data from Climate Central, the Washington, D.C. area is almost guaranteed to undergo a catastrophic flood by the year 2100. (Jason Aldag/The Washington Post)

By the end of this century, as sea levels rise, as much as $7 billion worth of property in the District will routinely be threatened by storm-driven floodwaters, according to a new analysis, including 1,000 homes, three military bases and a broad swath of the Mall.

With tides on the Atlantic Coast generally forecast to rise two to four feet by 2100, the nation’s capital faces increasing odds that a big storm will blow up the Potomac River and raise local waters by at least eight feet, the analysis says — roughly a foot higher than the damaging floods that accompanied Hurricane Isabel in 2003.

The report, set for release Tuesday by the nonprofit Climate Central, maps the areas at risk in unprecedented detail, cataloguing vulnerable government facilities, roadways, cultural sites and private houses. At eight feet, for example, the Washington Navy Yard, Fort McNair and much of Joint Base Anacostia-Bolling would be inundated, the report says. So would the Maine Avenue waterfront, subsidized apartments along the Anacostia River and national memorials honoring Jefferson, King and Lincoln.

“In D.C., we’re talking about a relatively small slice of land that’s vulnerable. But it’s an area of great cultural, economic and even military importance,” said Ben Strauss, vice president for climate impacts at Climate Central, an organization of scientists and journalists that is assessing flood risk from sea-level rise for the entire U.S. coastline.


New maps show future storm surge

Museums and federal office buildings along a low-lying stretch of Constitution Avenue NW, which flooded after a week of heavy rains in 2006, would be protected from a tidal surge by a recently-completed levee that straddles 17th Street NW, not far from the White House and the Washington Monument.

But District officials said much of the city’s waterfront could be transformed by the threat: The highest flood on record in the city was 7.9 feet in 1933. But by 2100, Climate Central estimates that the District would be facing an eight-foot flood roughly every 10 years.

“That’s very routine, probably to the point that people will have to change their way of operating completely,” said Brendan Shane, chief of sustainability for the District Department of the Environment. “Things will be walled off, jacked up or moved. You’re looking at a very different use of the landscape in that scenario.”

In addition to the District, Climate Central was set to release detailed maps and data Tuesday for Maryland, Virginia and Delaware. All told, Strauss said, more than $42 billion worth of property across the three states will be threatened by regular flooding as sea levels rise, imperiling 116,000 homes and 3,400 miles of roadway.

The most vulnerable spots are Norfolk, Va.; Ocean City, Md.; and other places hit hard by the ocean. But Baltimore’s Inner Harbor and the oldest parts of Annapolis are also at risk, as are many communities along the Potomac, such as Old Towne Alexandria.

State and local officials are working to respond to the threat, with varying degrees of urgency.

In Maryland, which has 3,100 miles of coastline, sea-level rise has been on the agenda for close to 15 years. The state has shifted open-space acquisition away from the coast to avoid preserving land that one day will be underwater. State agencies are required to take sea-level rise into account when planning new buildings and infrastructure. And last year, a Maryland commission recommended adopting an official forecast of two feet of sea-level rise by 2050 — at the high end of the scientific spectrum.

“Here in this region, Hurricane Isabel was a big wakeup call. Then [Hurricane] Sandy. And then these heavy precipitation events over the last year,” said Zoe Johnson, program manager for climate change policy at the Maryland Department of Natural Resources. “There’s been a lot of interest in this type of planning.”

By contrast, Virginia, which has 3,400 miles of coastline, has been struggling to reach political consensus since at least 2012, when Republican state lawmakers refused to fund a study on “sea-level rise,” but consented to a study of “recurrent flooding.”

The resulting report, by the Virginia Institute of Marine Science, nonetheless predicted that tides along the Virginia coast would rise by three to five feet by 2100. Since then, Republican governor Robert F. McDonnell has been replaced by Democrat Terry McAuliffe, who last week convened his own statewide commission on climate change. McAuliffe gave the group a year to come up with some “big ideas” that could be implemented before his four-year term is over.

In the District, planning for sea-level rise is just getting underway. While local officials have long had strategies for combating historic flooding, District officials earlier this year hired a consulting team for the first time to start assessing the city’s future risks, not only from higher ocean tides but also from other effects of climate change, including extreme heat and more frequent and heavy precipitation.

The team includes Katharine Hayhoe, director of the Climate Science Center at Texas Tech University. An evangelical Christian, Hayhoe gained national fame after appearing on the Showtime documentary about climate change, “Years of Living Dangerously.”

The city is also consulting with federal agencies, such as the National Park Service, which manages the Mall and other big chunks of vulnerable land in the District. The Pentagon is conducting its own assessment of vulnerability to climate change at the nation’s military bases, including those in the District.

Meanwhile, any change in the city’s flood-risk assessment that makes building more expensive could draw the wrath of developers.

“It’s going to be an interesting few months as this discussion progresses, particularly as you have more concrete numbers,” Shane said. “With Climate Central, there’s one map that shows risk levels. But there’s another map for current building codes, and they’re different.

“So we may be in this limbo area for a while, where we have competing visions for what the impacts of the climate change may actually be.”