As sea levels rise, tidal flooding along the U.S. coast is likely to become so common that parts of many communities, including the nation’s capital, could become unusable within three decades, according to a new report from the Union of Concerned Scientists.

 

Rising sea levels create a higher platform for tides and storm surges. Scientists compare the effect to slam dunks in basketball: Raising the gymnasium floor would increase the number of slam dunks per game.

 

The report’s projections build on recent studies that documented a dramatic increase in tidal flooding over the past half century. Many coastal communities are already struggling to cope with routine flooding that makes streets impassable and overwhelms storm-water systems.

 

Using a methodology similar to those of the recent studies, scientists projected the trends 15 to 30 years into the future at 52 sites around the country. The study used moderate sea-level rise projections from the National Climate Assessment, a U.S. government report based on input from some 300 scientists, engineers, industry officials and other specialists.

 

The Union’s study posits a sea rise of about 5 inches over the next 15 years and about 11 inches over 30 years. Under that scenario, the new study found, most of the 52 locations could experience the equivalent of twice-monthly coastal flooding within 15 years. In 30 years, one in three of the locations would average 180 or more tidal floods a year.

 

Washington, D.C., is among the most vulnerable. By 2045, it could experience nearly 388 tidal floods a year, the study projected.

 

The study also projected that flooding will grow more extreme. In 15 years, the tides that cause today’s so-called nuisance floods could become far more extensive in seven cities, enough to threaten lives and property.

 

The scientists recommended that communities, states and the federal government begin flood-proofing homes and infrastructure. They said development should be limited in vulnerable areas, while officials should examine the use of sea walls and other adaptations to higher seas.