Tidal flooding - you could be at risk even on sunny days

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Tidal flooding, also known as sunny day flooding, king tide flooding, and nuisance flooding, is the temporary flooding of low-lying areas near a coast.

At-risk areas can experience this flooding multiple times a year. Search your property on Risk Factor to understand if tidal flooding is a threat to your home or community. Being aware of your risk allows you to prepare for and mitigate risks before they become a reality.

Definition

Tidal flooding, also known as sunny day flooding, king tide flooding, and nuisance flooding, is the temporary flooding of low-lying areas near a coast. Tidal flooding usually occurs through the combination of winds, offshore storms, and full moon cycles during high tide events such as full moons and new moons. At-risk areas can experience this flooding multiple times a year. Tidal flooding is incorporated into our models through the addition of coastal tide gauge station readings to adjust local water levels for integration into our modeled flood risk layers. 

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Tidal Flooding 

Tidal flooding on Risk Factor 

Tidal flooding usually occurs through the combination of winds, offshore storms, and full moon cycles during high tide events such as full moons and new moons. Tidal flooding is incorporated into the First Street Foundation Flood Model through the addition of coastal tide gauge station readings to adjust local water levels for integration into our modeled flood risk layers.

Sea levels are rising

Most of America’s coast is experiencing rising seas caused by global ice melt, thermal expansion, changes in ocean circulation, and local land sinkage. Sea level rise makes high tides higher, which puts more pressure on coastal drainage systems. Higher seas also lead to higher storm surge from hurricanes and other storms, resulting in deeper floods that travel farther and last longer.

The impact of higher seas

When Hurricane Katrina hit in 2005, its 27.8 foot storm surge toppled New Orleans’ levees causing massive flooding; the storm ultimately claimed 1833 lives and caused more than $105 billion in damages. Scientists estimate that its storm surge and flooding was 15-60 percent higher than it would have been in 1900, when local sea levels were 2.4 feet lower. First Street Foundation found that sea level rise since 1970 contributed to approximately 57,000 more homes being impacted by Hurricane Irma’s storm surge.

Many coastal areas are seeing floods more often even when there are no storms, as local sea levels increase the number of “sunny” day floods caused by high tides. There are now over 40 locations in the U.S. with accelerating high tide flooding trends, including Washington D.C. which saw 22 days with high tide floods in 2018.

Sea surfaces are getting warmer

A warmer atmosphere also means warmer oceans. The sea’s surface temperature is 1.5˚F warmer than it was in 1950 and will rise another 0.5˚F by 2050. Higher ocean surface temperatures fuel hurricanes and offshore storms with more water and power, so these systems reach further inland and further north, are more intense, and last longer.

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Road covered by floodwater left in the wake of Hurricane and Tropical Storm Harvey on August 31, 2017 near Houston, Texas. (Scott Olsen / Getty Images)

The impact of warmer seas

When Hurricane Harvey hit Houston in 2017 the Gulf of Mexico was experiencing record-breaking ocean temperatures, reaching upwards of 86 F. The warm waters both sustained and intensified the storm, feeling it with enough moisture to produce up to 60.58 inches of rainfall in some areas, and lasting over 4 days, making Hurricane Harvey the country’s wettest tropical cyclone ever recorded.

Warmer ocean atmospheric temperatures also played a strong role in Hurricane Dorian’s slow movement in 2019, when it stalled over the Bahamas for more than a day and at one point slowed to just 1.2 miles per hour. The duration of the storm and warm ocean temperatures contributed to significant rainfall, totaling 36 inches.

Learn more

Flood Model Methodology - Calculating property-level risk

What is urban flooding? - Visit Risk Factor to check your risk

Flood Factor probabilities - The likelihood of water reaching a home

Environmental Changes

 

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