The data show that buyouts were disproportionately concentrated in wealthy and densely populated counties. The reason, according to the report’s authors, is that local officials must request federal funds for buyouts — and then successfully navigate a series of bureaucratic requirements — and wealthier jurisdictions are more likely to have the staff and expertise necessary to do that.

“Buyouts require resources and capacity to administer,” said Caroline M. Kraan , another of the study’s authors. “Not all governments may be equally able to access the program.”

In addition, once local officials receive the federal funds, buyouts aren’t evenly distributed within those counties, nor are they distributed according to risk levels alone. Instead, counties tend to use the money to buy and tear down homes in poorer neighborhoods, the authors found.

There are different possible explanations for that, according to A.R. Siders, a professor at the University of Delaware and one of the paper’s authors.

Officials might feel that the poorer neighborhoods are genuinely the most vulnerable, Ms. Siders said. Those officials might also conclude that a given amount of federal dollars can go further purchasing a greater number of low-value homes, rather than buying just a handful of more expensive beachfront properties for the same amount.

Another explanation, she said, could be that local officials “are using the buyouts as an opportunity to get rid of neighborhoods that they don't feel are desirable parts of their community,” Ms. Siders said.

The research, however, wasn’t designed to examine which of those motivations was most prevalent. “All of these things are probably occurring,” she added.