Sunny Day Flooding is Increasing

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Flooding has hit the news just as hard as wildfires and other natural disasters that have impacted people, cities, and vulnerable ecological habitats around the world. Flooding comes as a result of higher than average sea levels, as well as the increase in the strength and duration of storms, hurricanes, tropical cyclones, and other weather events.

Flooding doesn’t limit itself to spaces near bodies of water; deserts and mountainous areas have been hit by flooding, as have near-coastal areas. Now, researchers are turning their eyes towards another kind of rising flood danger.


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Tidal Flooding

Tidal flooding, or sunny day flooding, hits during periods of time that people least expect. While people associate flooding with storms, hurricanes, or certain seasons, sunny day flooding can occur on days when there hasn’t been any rainfall or a cloud in the sky. Scientists point to this trend of sunny day flooding as one way that climate change is affecting our natural environment.

The frequency of tidal flooding can be attributed to some of the symptoms of climate change, such as the rise in sea level, the erosion of coastal barriers like reefs and sandbanks, as well as the gradual sinking of lands located on sediment rather than bedrock. These slow but consistent changes lead to more flooding in coastal areas, clogged storm drains, considerable erosion, damage to infrastructure and concerns for public health.

High tide flooding in Port Orchard, Washington, on Jan. 6, 2010. (Ray Garrido, courtesy of Washington Department of Ecology)
High tide flooding in Port Orchard, Washington, on Jan. 6, 2010. (Ray Garrido, courtesy of Washington Department of Ecology)

Research has shown that the instances of tidal flooding have increased on the Atlantic, Pacific, and Gulf coasts of the United States by 300-925% since the 1960s. NOAA, the National Oceanic and Atmospheric Administration, has collected data that shows the rise of flooding in helping push out communities in the Louisiana bayous and the Marshall Islands to gradually disappear. Communities in Florida and Louisiana are especially vulnerable due to their proximity to the ocean and their low elevations; climate change will cause sunny day flooding to increase, pushing residents out of their homes more and more.

The Science Behind Sunny Day Flooding

Tidal flooding got its name because the flooding aligns with the highest or strongest tides during new or full moons. The sun and the moon are aligned with Earth, causing the water to rise higher as these bodies exert their gravity on the water. These are called ‘king’ or ‘spring’ tides and can come along a few times a year to cause major flooding in vulnerable areas. Unlike the floods associated with a hurricane’s storm surge, tidal flooding can come up through a city’s sewers and inundate streets and neighborhoods from below. These different flood types can be difficult to differentiate from one another, just as they can be challenging to model and predict in combination with other meteorological forces.

Climate Change and Tidal Flooding

Tidal flooding is set to increase as the effects of climate change continue. As sea levels rise worldwide, tidal flooding will increasingly become a situation that coastal cities will have to learn to deal with. A moderate estimate is that sea level is rising a foot per century; however, this estimate could be more along the lines of a foot a decade. By 2035, well over 170 US cities or more could be consistently under floodwaters.

High tide flooding events have increased around the U.S., but especially off the East Coast. | Download PDF
High tide flooding events have increased around the U.S., but especially off the East Coast. Source: NOAA.

Between 2000 to 2019, these tidal flooding events increased by 190 percent in the Southeast, and by 140 percent in the Northeast according to a report issued by NOAA entitled, 2018 State of High Tide Flooding and 2019 Outlook.  

Reference

French, Kristin. Why Do Floods Sometimes Happen on Sunny Days? 29 November 2017. Retrieved from https://blogs.ei.columbia.edu/2017/11/29/why-do-floods-happen-on-sunny-days/

Sweet, W., Dusek, G., Marcy, D. C., Carbin, G., & Marra, J. (2019). 2018 State of US High Tide Flooding with a 2019 Outlook.

U.S. ties record for number of high tide flooding days in 2018.  July 10, 2019.  NOAA

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