June 2003 Feature: NOS's Environmental Sensitivity Index Maps Help Scientists Protect Vulnerable Shorelines
When an oil or chemical spill occurs, responders must decide quickly which coastal locations need the most protection. They need a systematic way to determine which areas are most vulnerable to the spill, and which areas can be protected with existing resources. Federal, state, and local responders rely heavily on color-coded Environmental Sensitivity Index (ESI) maps that serve as quick references to a threatened shoreline. ESI maps indicate a coastal areas level of vulnerability to oiling. They also pinpoint the locations of plants, animals, and areas that people use that could be harmed by a spill. Scientists from NOSs (OR&R) work with other state and federal partners to produce ESI maps long before an oil or chemical spill occurs.
In the ESI maps, shorelines are color-coded and numerically ranked on a scale of 1 to 10. The most sensitive areas, such as tidal flats, swamps, and marshes, are indicated by warm colors like red and orange, and are given a ranking of 10. The least sensitive areas, such as rocky headlands and gravel beaches, are indicated by cool colors like blue and purple, and are given a ranking of 1. Areas of moderate sensitivity are green. Colored polygons denote habitats for plants and animals.
Depending on the season, oil spills can affect breeding sites, migrations, and life stages of different animals. ESI maps respond to this threat by classifying organisms into seven categories, which in turn are divided into sub-groups of organisms with similar oil sensitivities. ESI maps indicate where the most sensitive species live, and what they use the habitat for, such as spawning, or over-wintering.
Coastal zone managers and oil spill planners use ESI maps to identify the seasons when a particular species is most vulnerable, allowing them to establish protection priorities for a cleanup effort. Sensitive animals and habitats are denoted by special point symbols.
For example, a symbol of a seal identifies habitats used by gray and harbor seals. To protect certain endangered species from possible human disturbances, ESI maps do not show exact locations of sensitive habitats.
ESI maps categorize human use areas that are especially susceptible to oil spills. These include:
NOAA researchers are working with federal, state, and private industry partners to improve the ESI mapping system to extend beyond spill response. By incorporating geographic information systems information, higher quality and more frequently updated maps can be produced and distributed in various digital formats. In addition, OR&R is developing digital ESI databases for high-priority coastal areas, and establishing standards for ESI data users. These guidelines will help scientists exchange data, and provide a means for evaluating data quality. The guidelines also will permit the development of computer applications that display ESI maps.
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