High tide flooding in the United States continues to increase

[Front Street in Beaufort, North Carolina, during a so-called king tide. High tide flooding causes frequent road closures, overwhelmed storm drains and compromised infrastructure. (Christine Burns / NC King Tides Project UNC-IMS]

[Written by NOAA] Coastal communities across the United States continued to experience record flooding at high tide last year, forcing their residents and visitors to contend with flooded shorelines, streets and basements – a trend that is expected to continue in 2021. High water levels have affected coastal economies. , tourism and critical infrastructure like waste and stormwater management systems, according to a new NOAA report.

The report, 2019 State of High-Tide Flooding and 2020 Outlook, documents changes in high-tide flooding patterns from May 2019 to April 2020 at 98 NOAA tide gauges along the U.S. coast, and provides an up-to-date outlook. flood for these locations for the next weather condition. year, May 2020 to April 2021, and projections for the next decades

High tide floods, often referred to as “nuisance” floods or “sunny floods”, are becoming more frequent due to years of relative sea level rise. This occurs when tides reach between 1.75 and 2 feet above the average daily high tide and begin to spill into the streets or bubble up from the storm drains. As sea level rise continues, the destructive flooding that occurred decades ago only during a storm now occurs more regularly, such as during a full moon tide or with a change in the prevailing winds or currents.

“America’s coastal communities and their economies are suffering from the effects of high tide flooding, and this will only increase in the future,” said Nicole LeBoeuf, acting director of NOAA’s National Ocean Service. “NOAA is committed to working with coastal communities to provide the information and data they need to address the problem of high tide flooding now and in the years to come as sea levels continue to rise. to increase.”

According to the report, US coastal communities experienced a median flood frequency of four days in 2019, just below the record set last year. However, 19 locations along the east and Gulf coasts have set or tied records where rapidly increasing trends in high tide flooding have emerged.

[Flooding during a perigean spring tide in Charleston, SC. From NOAA]

In 2019, the Southeast saw a 3x increase in days of flooding compared to 2000. For example, Charleston, South Carolina experienced 13 days of flooding reaching damaging levels, compared to only two typical days in 2000. Along the western Gulf, percentage increases were greatest, greater than 5 times. In Texas, Sabine Pass and Corpus Christi experienced 21 and 18 days of flooding in 2019, and in 2000 these places would typically experience only about one and three days, respectively.

“As a Chesapeake Bay resident, I see the flooding firsthand and it’s getting worse. Records seem to be set every year,” said William Sweet, Ph.D., oceanographer for NOAA’s National Ocean Service and lead author of the report. “Communities are grappling with this growing problem. Fortunately, NOAA’s tide gauge network is watching closely and helping to provide guidance on the disruptive floods likely to occur next year and for decades to come.

Sweet and his co-authors project that from May 2020 to April 2021, the national frequency of high-tide flooding is expected to accelerate, with US coastal communities experiencing an average of 2-6 days of flooding over the coming year. . Communities along the northeastern and western gulf coasts are expected to experience even more flood days.

By 2030, long-term projections show seven to 15 days of high tide flooding for coastal communities nationwide. By 2050, this increases to 25 to 75 days, suggesting high tide flood levels could become the new high tide. This long-term outlook is based on the range of relative sea level rise, using 2 scenarios from the Fourth National Climate Assessment considered most likely to occur by 2030 and 2050 – low-intermediate and intermediate.

NOAA maintains an ocean observing infrastructure, including more than 200 permanent water level stations on the U.S. coasts and Great Lakes, and is the national authoritative source for real-time and historical data, forecasts , predictions and scientific analyzes that protect life, the economy and the environment on the coast.

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