New Hampshire’s Sea Level Is Rising

The sea level off New Hampshire’s coast is up to 7 inches higher than it was in 1950.¹ This increase is mostly due to changes in ocean circulation² Solutions can be complicated because a lot of important infrastructure on the coast is shared by both city and state, so mitigation efforts will need to be coordinated.³ There are already over 2,544 properties at risk from from tidal flooding in NewHampshire.⁴ The state is planning over $600,000 in sea level rise solutions, which include restoration projects, research and outreach, flood prevention for roads, and fortifying coastal wetlands.

Sea level rise is speeding up

The sea level around nearby Boston, Massachusetts, has risen by around 7 inches since 1950. Its speed of rise has accelerated over the last ten years and it’s now rising by about 1 inch every 10 years.¹ Scientists know this because the sea level is measured every 6 minutes using equipment like satellites, floating buoys off the coast, and tidal gauges to accurately measure the local sea level as it accelerates and changes.⁵

While there are four main causes of sea level rise in New Hampshire, ocean circulation is the largest contributor.¹ Because changes in ocean circulation are causing coastal storms such as Nor’easters to increase in frequency and intensity, New Hampshire is particularly vulnerable to an increased rate of sea level rise in the future. Click here to learn more about these causes.

Most flooding happens in the winter

The highest tides in New Hampshire occur during nor’easters. These wintertime storms push more water to the coast, raising high tides even higher, especially when combined with an increased gravitational pull from the moon. In places like Boston, these tides are typically over a foot and a half higher than normal high tides.¹ Add that to the 7 inches of sea level rise since 1950 and you end up with flooding even on sunny days.

Solutions aren’t simple

Solving for sea level rise can be complicated in New Hampshire because most mitigation efforts will need to be organized as joint efforts. New Hampshire has a lot of municipality and state shared infrastructure, so mitigation efforts must be coordinated in order to succeed.³ In addition, the state’s coastal habitats and communities are both at risk from sea level rise and flooding, but solutions for each affect the other. The Hampton-Seabrook Estuary, for example, is host to 5,000 acres of tidal flats and coastal estuaries, which provides a critical habitat for important wildlife and serves as a buffer to protect inland communities.⁶ For the estuary to survive, protective barriers such as seawalls will need to be removed so waters can shift inland. However, there are existing communities in the areas the estuary would shift into, and these communities may block the removal of these barriers.⁷

When the ocean rises high enough, high tides cause flooding even on sunny days. Even though the sea level has only risen by around 2 and a half inches, tidal flooding has increased by 260% in some areas of New Hampshire since 2000.¹⁰

Flooding even when there’s no rain

Drainage systems are designed to channel excess rainwater from the streets and drain it into the sea. But with the pressure from rising sea levels and higher tides, seawater can get pushed into these pipes and spill out into the streets. This causes flooding even on days without rain.

Increased storm surge flooding

Unfortunately, slightly higher sea levels make hurricanes even more damaging. Just a few more inches of sea level rise allow a hurricane to push more water onto the land, even if the hurricane itself doesn’t make landfall.

There’s a lot at risk from sea level rise and flooding in New Hampshire. Even though the state has the least amount of tide-influenced coastline in the country, with less than 20 miles, the coast and its wetlands support diverse habitats that are at great risk from sea level rise.¹⁴ Birds such as the Osprey, Northern Harriers, Least Terns, and more depend on the Hampton-Seabrook Estuary, however rising seas have caused breeding grounds to disappear, triggering a rapid decline in numbers and putting the species at risk of extinction.⁶

In addition, there are many assets and infrastructure on the coast of New Hampshire that are shared by both the state and municipalities, including roads and wastewater treatment facilities. Failure to coordinate solutions for the effects of sea level rise could worsen flooding and storm surge disasters statewide.³

In Hampton Beach there are 727 residential properties already at risk from repeated tidal flooding, by 2033 that number will increase to 841 as sea levels rise. In Portsmouth, 169 properties at risk will turn into 199 within 15 years. And in Dover there are 102 properties at risk, which will become 122. Click here to explore other coastal areas in Virginia that are at risk at FloodiQ.com.

What can you do?

Individuals, mayors, legislators, governors, and Congress can work together to build protections before flooding, to build back stronger after flooding, and to create plans that future-proof our communities. Click here to see what solutions can help protect your home or what your community can do.