WASHINGTON- Along much of America's coasts, the type of flooding that is more annoying than dangerous has jumped more than fivefold in the last 50 years, the federal government reported Monday.
Scientists blame rising seas, saying this is one of the ways global warming is changing everyday lives.
The National Oceanic and Atmospheric Administration studied coastal trends in what it calls nuisance flooding, where no one is hurt but people have to deal with flooded roads and buildings.
While scientists and the public spend a lot of time dealing with giant events, such as a hurricane, it is minor floods that people feel more often, though not as severely, said NOAA's Margaret Davidson.
"It's the stuff that keeps you from conducting your business or picking up your kids from school," Davidson said. "It is clear that changing climate and weather patterns will cause us to be increasingly inconvenienced and challenged in our everyday lives."
Oceanographer William Sweet looked at coastal sites across the nation, focusing on 25 places with records that go back beyond 1950. Fifty years ago the 25 sites averaged about 2.5 days of minor flooding a year. Now those places average about 14 days a year.
All 25 of those locations saw increases in the number of minor flood days; 22 of them saw more than doubling of nuisance flooding since the late 1950s and early 1960s. Those 25 cities have also seen sea level rise nearly half a foot since 1963.
The biggest increases are in the mid-Atlantic region. Charleston, South Carolina, San Francisco and Port Isabel, Texas, also showed more than four-fold increases in flooding.
Annapolis, Maryland, had the biggest percentage increase. From 1957 to 1963 it averaged 3.6 minor flood days a year; now it averages more than 39 a year. In 2011, Maryland's capital had 66 minor flood days.
University of Maryland environmental scientist Donald Boesch, who wasn't part of the report, said this type of event is probably more meaningful to people than the bigger and less frequent storms. He noted that sea level has risen about 8 inches in Annapolis since 1971.
"Simply stated, the cause of the increase in inundation frequency is sea level rise attributable to global warming," Boesch said in an email.
Sweet said sinking land and building construction are factors in the increased flooding, but not nearly as much as rising seas.
"It's going to become the new normal," Sweet said. "That is how we can identify with the impacts of sea level rise."
Sweet looked at increase nuisance flooding in Boston; Providence, Rhode Island; New London, Connecticut; Battery Park, Kings Point, and Montauk, New York; Atlantic City and Sandy Hook, New Jersey; Philadelphia; Lewes, Delaware; Baltimore and Annapolis, Maryland; Washington; Norfolk, Virginia; Wilmington, North Carolina; Charleston, South Carolina; Fort Pulaski, Georgia; Fernandina Beach, Key West and Mayport, Florida; Port Isabel, Texas; La Jolla, California; San Francisco, Seattle and Honolulu.