Credit: Michael W. Fincham

THE NATION'S CAPITAL IS NOT NEW ORLEANS. Washington, D.C., stands along the banks of the Potomac River, not the Gulf of Mexico. As with the city of New Orleans, however, part of Washington went underwater during past hurricanes. To keep it above water in the future, the city will start building new levees and a storm wall on the National Mall in hopes of keeping the Potomac River out of downtown D.C.

After the flooding of New Orleans from Hurricane Katrina, officials with the Federal Emergency Management Agency (FEMA) began re-examining its floodplain maps for Washington to figure out how the city could be protected from larger floods in the future. The dilemma facing Washington is familiar to state and local planners in the Tidewater regions around the Chesapeake as they have to redraw floodplain maps to allow their communities to participate in the National Flood Insurance Program (NFIP).

While the Washington wall is not a solution for the Tidewater — nobody is going to build a storm wall around Dorchester County — it's a handy symbol of the problem. Low-lying regions are at greater risk from future storm surges and flooding — thanks to global warming. And planning for those risks calls for tough tradeoffs. After all, city planners don't see a storm wall in the shadow of the Washington Monument as a wonderful aesthetic addition to the National Mall. But $9 million for a storm wall could avoid $200 million for damages to museums, memorials, and office buildings. Homeowners in the Tidewater aren't happy about hoisting their houses above a newly defined floodplain, but it does give them some protection — and it qualifies them for federally subsidized flood insurance.

In Washington, FEMA wants new levees and a storm wall, because of its experience with past hurricanes and its fear of future storms. According to FEMA, Hurricane Isabel created more severe flooding in 2003 than did the historic August Hurricane of 1933, the storm that is still considered the most destructive Chesapeake hurricane over the last century.

Why more flooding in 2003? According to FEMA, the extra flooding from Isabel could be a result of a relative sea level rise of one foot since the 1933 storm. If sea levels continue to rise as predicted, then future storm flooding in Washington could be even greater. The current forecast from the U.S. Geological Service predicts sea levels will rise another one foot in the Chesapeake Bay (and the Potomac River) over the next 100 years. And that might be an underestimate. So far the observed sea level rise in the Chesapeake is running twice the global rate.

Sea level rise is only one worrisome prediction about global warming. Another is the forecast for more ferocious storms capable of even stronger storm surges. Whether it's created by human pollution or natural cycles, the recent warming has raised sea surface temperatures in the oceans, the globe's great reservoir of heat and the engine that drives its weather patterns. Warmer waters, according to most scientists, will lead to more violent storms, bringing new floods to Washington D.C. and to homes across the Tidewater region of Chesapeake Bay.

— Michael W. Fincham