Data from the Hampton Tide Gauge Show High Tide Flooding Occurred 36% of Recorded Days Between 2013 and 2020, Frequency Expected to Increase

Portsmouth, NH – A new report released by the New Hampshire Department of Environmental Services Coastal Program and its partners entitled, “A Summary of High Tide Flooding Recorded by the Hampton, New Hampshire Tide Gauge: 2013-2020,” describes the frequency of high tide flooding in Hampton, New Hampshire, based on an analysis of a tide gauge in Hampton Harbor, which was installed in December 2012. The analysis shows that between 2013 and 2020, at least one high tide flood occurred on 36% of all the days recorded by the tide gauge. High tide floods are defined as a high tide reaching above the local high tide flooding threshold of 10 feet referenced to mean lower low water (MLLW).¹ In the low-lying areas of Hampton, floodwaters inundate local roads and property when water levels reach 10 feet above MLLW.

Unfortunately, sea-level rise is expected to dramatically increase the frequency and severity of flooding in coastal areas of Hampton, NH. The 2020 New Hampshire Coastal Flood Risk Guidance recommends that coastal New Hampshire should plan for sea levels to rise 1.3 to 2.3 feet above 2000 levels by 2050. The Hampton Tide Gauge summary report estimates that, with 1 foot of sea-level rise, 65% of high tides that occur in Hampton could reach or exceed the 10 foot MLLW threshold for high tide flooding, and with 2 feet of sea-level rise, 95% of high tides would exceed the 10 foot MLLW threshold for high tide flooding. Between 2013 and 2020, the tide gauge only recorded one flood event to reach the “Major” flood threshold above 13 feet MLLW during the Nor’easter of January 2018. However, with 2 feet of sea-level rise, “Major” flood events could occur 27 times per year, on average. More detailed coastal flood modeling work is underway to better understand future inundation frequencies and severities expected in Hampton and other coastal New Hampshire communities.

The report findings confirm that residents, visitors, local decision-makers and emergency management officials should refer to the Hampton Harbor tide gauge 3-day forecast and real-time information that factor in weather conditions in addition to the more commonly used annual NOAA tide prediction tables to improve understanding of and responses to coastal flood risk. The Hampton Harbor tide gauge supports real-time forecasts and storm warnings issued for the protection of life and property. Looking ahead to the future, the report findings underscore the importance of advanced planning and action to mitigate sea-level rise and increasing flooding in Hampton and surrounding coastal New Hampshire communities. The report findings also support the need for continued investments in monitoring water levels and tidal inundation throughout the region.

“The tide gauge data summary confirms what many residents of Hampton Beach already know – high tide flooding is already occurring very frequently in their most low-lying neighborhoods,” said Kirsten Howard, Resilience Program Coordinator for the NHDES Coastal Program. “The tide gauge in Hampton Harbor is a valuable asset that deserves sustained investment and regular analysis to help track high tide and storm flooding as sea levels rise, and with this report we can get the data out to people who will use it.”

Since 2013, the Hampton Harbor tide gauge has been measuring water levels at 6-minute intervals on a near-continuous basis. The report summarizing the gauge data record was published by the New Hampshire Department of Environmental Services Coastal Program in partnership with NOAA’s Office for Coastal Management and National Weather Service, the Northeast Regional Association of Coastal and Ocean Observing Systems (NERACOOS), Charybdis Group LLC., and the Seabrook Hamptons Estuary Alliance and is available on the NHDES website.

Please contact NHDES Coastal Program Resilience Coordinator Kirsten Howard at (603) 559-0020 or kirsten.b.howard@des.nh.gov with inquiries about this release and the report.