FILE - Portsmouth, New Hampshire

Portsmouth, New Hampshire, on the Piscataqua River.

(The Center Square) – A new report finds that twice as many New Hampshire properties are at substantial risk of flooding as what federal maps show.

The report by the First Street Foundation found that there are 64,000 New Hampshire properties at substantial risk in 2020, and that number is expected to increase by 3,000 in the next 30 years. In contrast, the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps only identify 29,000 properties at substantial risk.

“This discrepancy exists because the Foundation uses the current climate data, maps precipitation as a stand-alone risk, and includes areas that FEMA has not mapped,” the report cites.

Matthew Eby, executive director of the First Street Foundation, told New Hampshire Public Radio that the report is unique because it includes property-specific flood risk information that is easily accessible.

“We've also taken that and then adapted it into the future so that you understand what the risk will be like in 30 years, so you have a full perspective for a property, and that is available to the individual now,” Eby said.

The report finds that 10.3 percent of all properties in the United States are at substantial risk for flooding, but the proportion is greater in New Hampshire, with 11.1 percent of properties at substantial risk in 2020.

When looking at New Hampshire properties that have any risk for flooding, the number increases to 86,800 properties at risk, and approximately one third of these properties have a 99 percent chance of flooding at least once over the next 30 years.

In non-coastal areas, the federal maps have significantly underestimated the number of properties at risk, the report says. In Hillsborough county, with 131,477 total properties, FEMA reported 3,881 properties at risk while First Street Foundation finds 13,159 properties at risk.

The Foundation also created an online tool called Flood Factor that allows homeowners to see the flood risk of their property.