Product Code Database
A storm surge, storm flood, tidal surge, or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as . It is measured as the rise in water level above the normal tidal level, and does not include waves.
The main meteorology factor contributing to a storm surge is high-speed wind pushing water towards the coast over a long fetch.Yin, Jianjun, et al. "Response of Storm-Related Extreme Sea Level along the US Atlantic Coast to Combined Weather and Climate Forcing". Journal of Climate 33.9 (2020): 3745–3769. Other factors affecting storm surge severity include the shallowness and orientation of the water body in the storm path, the timing of , and the atmospheric pressure drop due to the storm.
As extreme weather becomes more intense and the sea level rises due to climate change, storm surges are expected to cause more risk to coastal populations. Communities and governments can adapt by building hard infrastructure, like , soft infrastructure, like or , improving coastal construction practices and building social strategies such as early warning, education and evacuation plans.
For example, in Palm Beach on the southeast coast of Florida, the water depth reaches offshore, and out. This is relatively steep and deep; storm surge is not as great but the waves are larger compared to the west coast of Florida. Conversely, on the Gulf side of Florida, the edge of the Floridian Plateau can lie more than offshore. Florida Bay, lying between the Florida Keys and the mainland, is very shallow with depths between and . These shallow areas are subject to higher storm surges with smaller waves. Other shallow areas include much of the Gulf of Mexico coast, and the Bay of Bengal.
The difference is due to how much flow area the storm surge can dissipate to. In deeper water, there is more area and a surge can be dispersed down and away from the hurricane. On a shallow, gently sloping shelf, the surge has less room to disperse and is driven ashore by the wind forces of the hurricane.
The topography of the land surface is another important element in storm surge extent. Areas, where the land lies less than a few meters above sea level, are at particular risk from storm surge inundation.
In North America, extratropical storm surges may occur on the Pacific and Alaska coasts, and north of 31°N on the Atlantic Coast. Coasts with sea ice may experience an "ice tsunami" causing significant damage inland. Extratropical storm surges may be possible further south for the Gulf coast mostly during the wintertime, when extratropical cyclones affect the coast, such as in the 1993 Storm of the Century.
November 9–13, 2009, marked a significant extratropical storm surge event on the United States east coast when the remnants of Hurricane Ida developed into a nor'easter off the southeast U.S. coast. During the event, winds from the east were present along the northern periphery of the low-pressure center for a number of days, forcing water into locations such as Chesapeake Bay. Water levels rose significantly and remained as high as above normal in numerous locations throughout the Chesapeake for a number of days as water was continually built-up inside the estuary from the onshore winds and freshwater rains flowing into the bay. In many locations, water levels were shy of records by only .
After surge from a cyclone has receded, teams of surveyors map (HWM) on land, in a rigorous and detailed process that includes photographs and written descriptions of the marks. HWMs denote the location and elevation of floodwaters from a storm event. When HWMs are analyzed, if the various components of the water height can be broken out so that the portion attributable to surge can be identified, then that mark can be classified as storm surge. Otherwise, it is classified as storm tide. HWMs on land are referenced to a vertical datum (a reference coordinate system). During the evaluation, HWMs are divided into four categories based on the confidence in the mark; in the U.S., only HWMs evaluated as "excellent" are used by the National Hurricane Center in the post-storm analysis of the surge.
Two different measures are used for storm tide and storm surge measurements. Storm tide is measured using a Geodesy vertical datum (NGVD 29 or NAVD 88). Since storm surge is defined as the rise of water beyond what would be expected by the normal movement caused by tides, storm surge is measured using tidal predictions, with the assumption that the tide prediction is well-known and only slowly varying in the region subject to the surge. Since tides are a localized phenomenon, storm surge can only be measured in relationship to a nearby tidal station. Tidal benchmark information at a station provides a translation from the geodetic vertical datum to Sea level at that location, then subtracting the tidal prediction yields a surge height above the normal water height.
To allow for track or forecast uncertainties, usually several model runs with varying input parameters are generated to create a map of MOMs or Maximum of Maximums. For hurricane evacuation studies, a family of storms with representative tracks for the region, and varying intensity, eye diameter, and speed are modeled to produce worst-case water heights for any tropical cyclone occurrence. The results of these studies are typically generated from several thousand SLOSH runs. These studies have been completed by the United States Army Corps of Engineers, under contract to the Federal Emergency Management Agency (FEMA), for several states and are available on their Hurricane Evacuation Studies (HES) website. They include coastal county maps, shaded to identify the minimum category of hurricane that will result in flooding, in each area of the county.
Unexpected flooding in estuaries and coastal areas can catch populations unprepared, causing loss of life. The deadliest storm surge on record was the 1970 Bhola cyclone.
Additionally, storm surge can cause or transform human-utilized land through other processes, hurting soil fertility, increasing saltwater intrusion, hurting wildlife habitat, and spreading chemical or other contaminants from human storage.
A prophylactic method introduced after the North Sea flood of 1953 is the construction of dams and storm-surge barriers (). They are open and allow free passage, but close when the land is under threat of a storm surge. Major storm surge barriers are the Oosterscheldekering and Maeslantkering in the Netherlands, which are part of the Delta Works project; the Thames Barrier protecting London; and the Saint Petersburg Dam in Russia.
Another modern development (in use in the Netherlands) is the creation of housing communities at the edges of wetlands with floating structures, restrained in position by vertical pylons. Such wetlands can then be used to accommodate runoff and surges without causing damage to the structures while also protecting conventional structures at somewhat higher low-lying elevations, provided that dikes prevent major surge intrusion.
Other soft adaptation methods can include changing structures so that they are elevated to avoid flooding directly, or increasing natural protections like or .
For mainland areas, storm surge is more of a threat when the storm strikes land from seaward, rather than approaching from landward.
The 1900 Galveston hurricane, a Category 4 hurricane that struck Galveston, Texas, drove a devastating surge ashore; between 6,000 and 12,000 people died, making it the deadliest natural disaster ever to strike the United States.
The highest storm tide noted in historical accounts was produced by the 1899 Cyclone Mahina, estimated at almost at Bathurst Bay, Australia, but research published in 2000 concluded that the majority of this likely was wave run-up because of the steep coastal topography. However, much of this storm surge was likely due to Mahina's extreme intensity, as computer modeling required an intensity of (the same intensity as the lowest recorded pressure from the storm) to produce the recorded storm surge. In the United States, one of the greatest recorded storm surges was generated by Hurricane Katrina on August 29, 2005, which produced a maximum storm surge of more than in southern Mississippi, with a storm surge height of in Pass Christian. Another record storm surge occurred in this same area from Hurricane Camille in 1969, with a storm tide of , also at Pass Christian. A storm surge of occurred in New York City during Hurricane Sandy in October 2012.
|
|
