Storm surges
A storm surge, sometimes referred to as a tidal surge, is a phenomenon where water is pushed toward the shore by strong winds during a storm, often resulting in significant flooding, particularly in low-lying coastal areas. This event is characterized by the combination of high winds, low atmospheric pressure, and wave action, creating a dome of water that rises as the storm approaches land. The most dangerous impacts occur in the right front quadrant of a storm's path, where the surge can be amplified by the shape of the coastline and the slope of the Continental Shelf.
Storm surges are commonly associated with tropical storms and hurricanes, differing from tsunamis, which are caused by underwater earthquakes or volcanic eruptions. The height and reach of a storm surge can be exacerbated by rising sea levels due to climate change, increasing the vulnerability of coastal populations. Notable historical examples include Hurricane Katrina in 2005, which generated record-breaking surges that led to widespread destruction and ecological damage. Recent storms like Hurricanes Michael and Ian have also demonstrated the devastating potential of storm surges. The growing intensity of hurricanes, linked to climate change, raises concerns about future storm surge impacts, highlighting the urgent need for awareness and preparedness in vulnerable regions.
Subject Terms
Storm surges
Definition
A storm surge, or tidal surge, is water pushed toward the shore by the winds of a storm. The combination of high winds, low pressure, and wave action is what makes a storm surge. The rush of water, combined with the regular action of the tide, causes water to rise significantly higher. This influx of water can cause significant flooding, especially in low-lying coastal areas.
Storm surges occur when a tropical storm or hurricane makes landfall. The pressure in the center, or eye, of a storm is low enough that surface water is drawn upward in a dome, just as beverages may be drawn up through a drinking straw. As the storm reaches land, this dome of water piles up against the shoreline, and the area within the right front quadrant of the storm’s forward motion is in particular danger.
Storm surges are sometimes confused with tsunamis. A tsunami (from the Japanese word for “harbor wave”) is generated by an undersea earthquake or volcanic eruption that creates a set of waves that can grow in intensity as they reach shallow coastal regions. Storm surges only occur in the presence of tropical storms, hurricanes, or cyclones.
The amount of surge is related to the size of the storm, as well as the slope of the Continental Shelf. A shallow slope allows more water to travel inland, while a steeper slope limits the surge but poses a greater danger of generating a breaking wave. The effects of a storm surge are multiplied in confined areas such as harbors and can also be felt in inland rivers and lakes.
The National Hurricane Center (NHC) uses the sea, lake, and overland surges from hurricanes (SLOSH) model to determine which areas should be evacuated in the event of a storm surge. Storm factors taken into consideration by this model include forward speed, pressure, size, track, and wind speed. These factors are weighed against the timing of the tide and the topological configuration of the projected landfall.
Significance for Climate Change
The inland reach of a storm surge is dependent on the slope of the Continental Shelf and the height of the land above sea level. In the United States, most of the population on the Gulf of Mexico and the Atlantic coastline is a little more than three meters above sea level, making those areas particularly vulnerable. If the sea level were to rise as a result of climate change, the population’s vulnerability would increase significantly.
Waves and the action of the current during a storm surge can cause additional damage. Water weighs 2,205 pounds per cubic meter (1,000 kilograms per cubic meter), and the erosion of beaches and coastal highways is a particular problem. Moreover, the influx of saltwater on freshwater bodies disrupts local ecosystems. Salt water that travels far inland may not dissipate for weeks.
The storm surge associated with Hurricane Katrina in August 2005 was one of the most massive in US history, spanning an area between Grand Isle, Louisiana, and Mobile Bay, Alabama. The storm surge drove water from the Gulf of Mexico up into Lake Pontchartrain and the Mississippi River, which in turn breached the levees in the city of New Orleans and the surrounding areas. Lake Pontchartrain, normally about 0.98 feet (0.3 meters) above sea level, peaked at 8.60 feet (2.62 meters) above sea level. According to the US Geological Survey, more than 348 square miles (560 square kilometers) of land were eroded into the ocean. The Chandeleur Islands, which formed the easternmost point of Louisiana, were completely destroyed.
The human and financial impact of the Katrina storm surge on the northern Gulf Coast is well documented, but there was a significant ecological price as well. Retreating floodwaters carried raw sewage, pesticides, toxic chemicals, and other waste products into the surrounding wetlands. Overall, sixty national wildlife refuges were damaged as a result of Hurricanes Rita and Katrina. A contributing factor to the damage from the 2005 storm season was the ongoing loss of wetlands and barrier islands, which had previously protected the low-lying areas from the worst of the earlier hurricanes.
At 28 feet (8 meters) in some areas, the storm surge generated by Hurricane Katrina was the highest in US history. However, other hurricanes have recorded enormous storm surges as well. In 2018, Hurricane Michael, a Category 4 storm, made landfall on Florida's panhandle, bringing storm surge that was more than 20 feet high (6.1 meters), killing forty-five people, and causing $15 billion worth of damage. In 2022, Hurricane Ian also released a deadly storm surge in Florida, causing water levels to rise 15 feet (4.6 meters) above sea level. In January 2023, the National Oceanic and Atmospheric Administration (NOAA) warned that hurricanes were becoming stronger and more dangerous due to the effects of climate change. Indeed, the 2024 tropical cyclone season was extremely severe. Though the number of tropical cyclones was within the average range, the storms were far more intense, causing significantly greater damage than past years.
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