HAMPTON A recent report says waterfront property values would be collectively higher by the millions today if not for sea level rise, though a booming market leaves some real estate agents skeptical.

Flood iQ, an online database tool created by the First Street Foundation, states New Hampshire coastal properties missed out on $15 million in property value since 2005 due to sea level rise based real estate transactions, government property records and available sea level rise data. The database says tidal flooding has increased by 260 percent since 2000 and that it was brought on by 2 inches of sea level rise in that time.

First Street, a New York nonprofit, added New Hampshire, Maine, Massachusetts and Rhode Island to its database in January, the project starting with Florida, Georgia, South Carolina, North Carolina and Virginia.

Cameron Wake, a University of New Hampshire climatologist, said the report's methodology appears sound considering authors Jeremy Porter and Steven McAlpine looked at real market transactions to reach their estimates. In their original study of the market in Miami-Dade, Florida, published in June 2018, Porter and McAlpine stated they examined all real estate transactions in the region that occurred between 2005 and 2016. The duo was behind analyses of the recently added states as well.

"It examines the impact on the real estate market from transactions the price people have paid for those homes," Wake said. "It's a really robust statistical analysis."

The database can be searched by individual property, in some cases by city or region. Flood iQ stated properties at Hampton Beach collectively missed out on approximately $8 million since 2005, not including North Beach properties north of Winnacunnet Road.

Local Realtors and appraisers say the study appears to go against what they've seen in the market where prices for homes along the coast have continued to rise. Hampton Beach Realtor Tom McGuirk doubts homes at Hampton Beach could have missed out on that much value because of rising tides, saying flooding has always been a factor for people buying homes at the beach.

"It's a bunch of malarkey," said McGuirk, who grew up on Hampton Beach and owns McGuirk's Ocean View, a restaurant and hotel. "Really and truthfully, the properties that have flooding have always flooded in my lifetime."

The Union of Concerned Scientists last summer also warned of impacts of sea level rise on coast properties. The UCS cited data from Zillow to show approximately 2,000 New Hampshire properties could face chronic flooding by 2045. UCS defined chronic flooding to be 26 flooding events per year.

Portsmouth Realtor John Rice believes the Flood iQ study is legitimate based on his own experience selling homes around the Seacoast. He said home buyers today factor flooding into their negotiations for waterfront homes more than they did 20 years ago.

Rice said Flood iQ's projections for lost value might be higher than reality depending on how much its authors relied on appraised values rather than real estate transactions. He said appraisals are never as accurate as an actual sale price.

Still, he said he has seen sale prices drop by hundreds of thousands of dollars after home buyers learn about future costs related to flooding, insurance and local ordinances. He said one Rye home he sold dropped from $800,000 to $500,000 due to anticipated costs related to flooding. The buyers learned they would need to dig 2 feet under their home and raise their utilities to the first floor if they wanted to renovate.

Rice was part of the Coastal Risks and Hazards Commission, which released a 2016 report on how cities and towns could prepare for increased flooding. The report cited studies by the National Oceanic and Atmospheric Administration that said New Hampshire's sea levels could rise 6 inches to 2 feet by 2050, and 1.6 to 6.6 feet by 2100. The U.S. Global Change Research Program has since stated sea levels could actually rise by as much as 8 feet by 2100, though that projection is based on extreme scenarios.

Several Seacoast waterfront and marsh-side home owners say they are experiencing flooding more frequently today than did in years past, some having lived there for decades. Many Hampton Beach residents living along the marsh have been calling for town officials to look at ways of preventing flooding. Some say destructive high tides have become more frequent in the last couple years, totaling cars and damaging foundations.

The town of Hampton has since passed funding for flood studies at the beach, and voters in March will be asked to whether or not to pass an ordinance requiring homes built or significantly renovated along the marsh be raised on pilings. The warrant article has sparked debate in town over whether such an ordinance would infringe on property owners' rights since raising homes on pilings can cost tens of thousands of dollars.

Rice said the appeal of living on the Seacoast has not deterred those who can afford waterfront homes from moving there. While the homes are still being sold, the buyers seem more conscious than ever of flooding.

"You don't have hundreds of buyers coming to the Seacoast saying, 'I don't want to buy property on the water,'" he said. "You do have people coming and saying, 'It's on the water. What does this mean?'"