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Federally Declared Disasters

Sustainability Issue:



Federally Declared Disasters (LO4)


Number of federally declared natural disasters in the categories of tsunami, coastal storm, drought, earthquake, flood, freezing, hurricane, typhoon, dam/levee break, mud/landslide, severe ice storm, fire, snow, tornado, volcano, and severe storm per square mile




12/24/1964 - 6/15/2004, totaled

Data Sources:

Federal Emergency Management Agency, United States Department of Homeland Security. (2004). Federally Declared Disasters by Calendar Year. FEMA GIS and Data Solutions Branch. Washington, DC.

International Federation of Red Cross and Red Crescent Societies (IRRCRCS). (2002). World Disasters Report: Focus on Reducing Risk 2002.



In the 1990s, some two billion people were affected by disasters world-wide (IFRCRCS, 2002). No one is immune from disasters. Everyone is vulnerable, but some are more vulnerable than others. By examining historical disaster trends, one can see that it is not only weather related damage causing disasters. Flawed development patterns (e.g., rapid unplanned urbanization, deforestation, installation of non-flood-proof dykes, no early warning systems, etc.) are also exposing more people to disasters (IFRCRCS, 2002). For example, earthquake fatalities are not necessarily the result of an earthquake but rather ineffective building codes. Tornados sweeping away homes may not be a sign of strong winds as much as poorly sited housing. There is no doubt disasters are a threat to both built structures and human health and safety. Thus, the military must be sensitive to potential threats from the natural and built environment. The mission of the installation can be severely impacted by disasters if proper provisions are not in place.

This indicator measures the number of Federally Declared Disasters occurring between 1964 and 2002. Federally declared disasters are those disasters declared by communities to the federal government. Often times upon declaration, the federal government offers some form of relief to the community (IFRCRCS, 2002). Thus whether or not a disaster is declared depends largely on the resources of the community and the agressiveness of community leaders. Many disasters of significant consequences are not declared while some of relatively little consequences are declared. In other words, declaration may have little to do with severity. Nonetheless, federally declared disasters offer the best indication of a community's disaster vulnerability reduction efforts. It is simply vital to use local knowledge in interpreting the Federally Declared Disasters classifications.



This indicator can be updated annually based on Federally Declared Disasters by Calendar Year data, as collected in the National Emergency Management Information System (NEMIS) maintained by the Federal Emergency Management Agency (FEMA) (USDoHS. FEMA, 2004).



Click on "Declared (Numbered) Disasters" link and then on the 2009 "Historical Maps for All USA" counties link. Download the frequency by county data. Import the data into a GIS program and join it to the county boundary file. Add the "freq64_08" column to the county boundary shapefile. Divide the data by county area (sq. mi.) to create a Federally Declared Disasters indicator layer. You may need to derive county area in your shapefile attribute table by adding a column and using the "calculate geometry" option.


Indicator Measure:

The number of federally declared natural disasters in the categories of tsunami, coastal storm, drought, earthquake, flood, freezing, hurricane, typhoon, dam/levee break, mud/landslide, severe ice storm, fire, snow, tornado, volcano, and severe storm for each county was summed to obtain a 38-year total for natural disasters (FEMA, 2004). This sum was then divided by its respective county area (square miles) resulting in federally declared disasters per square mile. This distributes the data by area. Distributing the data by area allows for an equal comparison between large and small-area counties. In other words, it protects against a large-area county from a more vulnerable classification because it naturally has more occurrences compared to a small-area county. Statistical analysis resulted in a mean of 0.0239 disasters per square mile and a standard deviation of 0.1136. Using these statistics along with natural breaks in the data, the following classifications were determined.

Very Low Vulnerability
Less than 0.0245 disasters per square mile
Low Vulnerability At least 0.0245 but less than 0.0183 disasters per square mile
Moderate Vulnerability At least 0.0183 but less than 0.1375 disasters per square mile
Vulnerable At least 0.1375 but less than 0.1945 disasters per square mile
High Vulnerability 0.1945 or more disasters per square mile


Installations are often in two or more counties. Therefore, regional classifications are determined by a weighted average. The weighted average calculation determines what percentage of the installation is in each county, and that percentage is multiplied by that county's value. Those values for each county around the installation are then totaled to arrive at a regional value. This value is then subject to the same metric that determined the classification for the individual counties.


Example: Indicator Value for the Installation = (Percentage of Installation in County A* Indicator Value for County A) + (Percentage of Installation in County B* Indicator Value for County B)…etc.
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