The research report, published by Environmental Research Letters, found that existing flood maps accurately measured the risks along the coasts, but didn't capture nearly all the risk in inland areas.

Yet inland flooding is in some ways more perilous. A study by the National Hurricane Center found that more than half the Americans kille d by flooding during hurricanes and tropical storms over a 30-year period had died after the storms moved inland , presenting hazards like flash floods and mudslides and sweeping motorists off flooded roads.

That sounds like what’s happening in the Carolinas

And it’s many of the people affected by those hazards who don’t have flood insurance.

People near the coasts tend to know their risks. Owners of expensive beach houses often buy even more flood insurance than they have to, because the government’s mandatory coverage is capped at $250,000 per house plus $100,000 for the contents. On top of that, additional “layers” of coverage can be purchased from private insurers .

In the Carolinas, a quarter to half of the households near the coast are insured, said Ray Lehmann, a member of SmarterSafer, a coalition of taxpayer groups, environmental organizations, insurers and others that has pushed for flood-insurance reform.

Further inland, it’s another story.

“We’re talking about places in North Carolina where the coverage is less than 1 percent,” said Mr. Lehmann, also the director of finance, insurance and trade policy at the R Street Institute, a think tank that promotes free-market policies.