The study, by Climate Central, a New Jersey research group, looked at the 10-year flood risk zone — the area with a 10 percent chance of flooding in any given year — and estimated the zone’s size in 2050. Then the group counted up homes built there since 2010, using data from Zillow, a real estate company.
For eight states, including Connecticut, Rhode Island, Mississippi and South Carolina, the percentage increase in homes built in the flood zone exceeded the rate of increase in the rest of the state.
There are many reasons construction persists despite the danger. In some cases it’s urban sprawl, in others it’s a desire among government officials for property-tax revenues. But whatever the reason, this kind of building activity will “come back and bite,” said Benjamin Strauss, president and chief scientist of Climate Central, which produces and publishes research on the effects of global warming.
The researchers’ objective was to examine “the riskiest of the risky places” — those that “actually would predictably flood multiple times in the course of one mortgage,” Mr. Strauss said. “Even in a time of growing climate change awareness, lots of towns are building fastest in the riskiest places.”
There is overwhelming scientific consensus that rising temperatures will increase the frequency and severity of coastal flooding caused by hurricanes, storm surges, heavy rain and tidal floods. At the same time there is the long-term threat of rising seas pushing the high-tide line inexorably inland.
“America’s trillion-dollar coastal property market and public infrastructure are threatened,” said a report last fall from 13 federal agencies. “Many individuals and communities will suffer financial impacts as chronic high tide flooding leads to higher costs and lower property values.”
The data used for the study is limited in that it relies on what counties classify as new construction. For example, in some cases a county may identify as newly built an existing home that has in fact only been elevated, according to Peter Girard, a spokesman for Climate Central. But that is likely to account for a small share of homes in the report, he said.
Building in the very areas that will predictably flood creates two problems, according to Larry Larson, senior policy adviser with the Association of State Floodplain Managers. The first is financial: As flooding eventually exceeds what the houses were built to withstand, homeowners will face rising insurance costs.
“Their flood-insurance premiums are going to skyrocket,” Mr. Larson said. “It’s not going to be pretty.”
The second problem is safety, both for residents and emergency workers. “If that water rises, they’re going to have to send rescuers in there to get them out,” Mr. Larson said.
Beyond the seemingly universal appeal of waterfront living, the continued coastal construction reflects a variety of local factors, according to state and city officials, as well as home builders.
In Connecticut, where the number of homes built in high-risk areas increased at more than three times the rate elsewhere in the state, out-of-state buyers are buying older homes then tearing them down and building new structures in their place, according to Diane Ifkovic, the state’s coordinator for the National Flood Insurance Program.
When the state has instead tried to acquire some of those flood-prone homes itself, with the purpose of reverting the land to open space, local officials have resisted, she added, fearful of losing the property tax revenue. “We tried this after Sandy,” Ms. Ifkovic said. “There is a lack of political will.”