High-tide flooding days refer to “nuisance” flooding or “sunny day flooding,” and they are increasing because of climate change. These flood days occur when tides reach one or two feet above the daily average high tide in that particular location.
“NOAA’s high-tide flooding outlook is critical to the nation’s communities as they build their climate resilience,” Jainey Bavishi, assistant secretary of commerce for oceans and atmosphere and NOAA deputy administrator, said in a statement. “The increase in high-tide flooding has affected infrastructure in coastal communities across America, especially in underserved communities.”
Since 2000, the number of annual high-tide flood days affecting the Pacific Islands has increased by seven, or more than 250 percent. The western Gulf has received an average of eight more flood days per year, for an increase of almost 300 percent in the same time period.
As levels rise, it no longer takes severe weather to produce a high-tide flood day, or nuisance day, which means an increase in disruptions to the country's coastal communities, home to some 40 percent of the U.S. population.
A combination of sea-level rise and factors such as land subsidence and the loss of natural barriers, changes in local prevailing winds, shifts in ocean currents, and strong tidal forces can all help lead to high-tide flooding.
NOAA offers an online visualization tool to help understand the impacts of high-tide flooding and how to manage it.
High-tide flooding falls into three severity levels: Minor refers to when water levels reach 1.8 feet above average tide and may cause road closures; moderate is when the level reaches 2.8 feet and can cause damage to homes or businesses; and major is when flooding has reached 3.9 feet above average high tide. The major floods are destructive, can lead to evacuations, and cause damage to infrastructure and property.
