Analysis: Nearly 65,000 New Hampshire properties face flood risk

Flooded road in San Mateo County, California February 2017

Some 64,900 properties in new Hampshire face a “substantial risk” of flooding – far higher than the number included in a Federal Emergency Management Agency model – and risks will only be growing in the coming decades, according to a newly released report.

The analysis, released as part of a national study by the First Street Foundation, a nonprofit research and technology group, also found that New Hampshire properties are at a higher risk of flooding than most other states.

Nationally, according to the First Street Foundation Flood Model, 10.3% of all properties across the contiguous United States are currently at substantial risk of flooding, and 11.4% will be at substantial risk in 30 years. New Hampshire has a greater proportion of at substantial risk, the report found, with 11.1% – 64,900 – at substantial risk today and 11.6% – 67,900 – at substantial risk by 2050.

According to FEMA analyses, 29,000 New Hampshire properties are currently at risk and 32,000 will be at risk by 2050.

FEMA’s statistics don’t factor in climate change, and they don’t include millions of homes that have never been mapped for flood risk. To determine its numbers, First Street studied river, intense rainfall models and changing environmental factors into account by applying global climate model projections to forecast how flood risk will change over the next 30 years.

According to the First Street report, communities with the most properties at risk are:

Manchester, with 4,184 properties currently at risk (14% of all properties in the city) and 4,301 projected to be by 2050; Nashua, 2,648 in 2020 and 2,770 by 2050 (13% of all properties); Keene, 1,643 in 2020 (24%) and 1,684 in 2050; Concord, 1,483 in 2020 (12%) and 1,526 by 2050; Laconia, 1,481 (22%) and 1,502 by 2050; Portsmouth, 815 in 2020 (13%) and 1,104 by 2050; Lebanon, 809 in 2020 (19%) and 820 by 2050; Claremont, 695 in 2020 (14%) and 707 in 2050; Dover, 648 in 2020 (8%) and 724 in 2050; and Derry, 646 in 2020 (9%) and 690 in 2050.

But the report found that the list is different when ranked by the growing risk faced by communities, topped by Portsmouth and followed by Hampton, Dover, Derry, Nashua, Exeter, Milford, Rochester, Londonderry and then Concord.

The communities with the greatest proportion of properties at risk are Littleton (27%), Keene (24%), Laconia (22%) Hudson (20%); Lebanon (19%) Franklin (15%); Claremont (14%); Manchester (14%); Berlin (13%); and Hampton (13%).