A rise in local tidal waters – fueled by global warming – virtually guarantees record flooding in Washington, D.C. over the next century, concludes a new analysis on sea level rise and flood risk.

The analysis from Climate Central — a non-profit science communication organization based in Princeton, N.J. — finds that the cumulative risk of a record-setting flood grows by the decade as sea levels rise.

“I would say the headline is that Washington, D.C. faces significant risk of record high floods within the coming few decades,” says Ben Strauss, Climate Central’s vice president for climate impacts.

Tidal flooding occurs most commonly in Washington from coastal storms — such as nor’easters and hurricanes — which can push a surge of water from the Atlantic up the Chesapeake Bay and Potomac. Due to predicted sea level rise of two to four feet over the next century, these floods are expected to exceed levels observed in the past. (Note: these tidal flooding events are distinct from flood events that originate upstream from heavy snow melts in the mountains and/or non-coastal heavy rain events. Occasionally, flooding occurs on the Potomac in Washington due to water pouring in from both directions, upstream and downstream.)

The Climate Central analysis finds that by 2100, there is a 98 percent chance of a record flood event occurring, which combined with sea level rise, raises water levels 8-feet in Washington.  There is even an 85 percent chance of a 10-foot flood by 2100.

Hurricane Isabel, by comparison, raised the water level of the Potomac just over 7 feet in 2003.

The percent chance of a record-setting 8-foot flood based on a mid-level sea level rise forecast by decade. (Climate Central)

Due to sea level rise, the risk of a record-setting flood by the end of the century increases by a factor of 6, the analysis finds.  Without sea level rise, the annual risk of an eight foot flood is just two percent, compared to 11 percent with sea level rise by 2100.

(Climate Central)

The analysis was released online Tuesday morning and features an interactive tool which allows users to visualize the amount of land inundated as flood waters rise.  The animation below illustrates which areas in D.C. will be inundated by water for floods of two, five and 10 feet.

Animation of water rise of 2, 5 and 10 feet (Climate Central)

The interactive tool, embedded below, allows you to pan and zoom to visualize the effects of flooding, and  also includes overlays which highlight vulnerable communities not only in D.C. but also Virginia, Maryland, and Delaware.

“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,” Strauss said in a story by the Post’s Lori Montgomery, which ran in today’s print edition.


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