OverviewThe multiple hazard index for the United States Counties was designed
to map natural hazard relating to exposure to multiple natural disasters. The index
was created to provide communities and public health officials with an overview
of the risks that are prominent in their county, and to facilitate the
comparison of hazard level between counties. Most existing hazard maps focus on
a single disaster type. By creating a measure that aggregates the hazard from
individual disasters, the increased hazard that results from exposure to
multiple natural disasters can be better understood. The multiple hazard index
represents the aggregate of hazard from eleven individual disasters. Layers
displaying the hazard from each individual disaster are also included.
The hazard index is displayed visually as a choropleth map,
with the color blue representing areas with less hazard and red representing
areas with higher hazard. Users can click on each county to view its hazard
index value, and the level of hazard for each individual disaster. Layers
describing the relative level of hazard from each individual disaster are also available
as choropleth maps with red areas representing high, orange representing
medium, and yellow representing low levels of hazard.Methodology and Data CitationsMultiple Hazard Index
The multiple hazard index was created by coding the
individual hazard classifications and summing the coded values for each United
States County. Each individual hazard is weighted equally in the multiple
hazard index. Alaska and Hawaii were excluded from analysis because one third
of individual hazard datasets only describe the coterminous United States.
Avalanche Hazard
University of South Carolina Hazards and Vulnerability
Research Institute. “Spatial Hazard Events and Losses Database”. United States
Counties. “Avalanches United States 2001-2009”. < http://hvri.geog.sc.edu/SHELDUS/
> Downloaded 06/2016.
Classification
Avalanche hazard was classified by dividing counties based
upon the number of avalanches they experienced over the nine year period in the
dataset. Avalanche hazard was not normalized by total county area because it
caused an over-emphasis on small counties, and because avalanches are a highly
local hazard.
None = 0 AvalanchesLow = 1 AvalancheMedium = 2-5 AvalanchesHigh = 6-10 Avalanches
Earthquake Hazard
United States Geological Survey. “Earthquake Hazard Maps”.
1:2,000,000. “Peak Ground Acceleration 2% in 50 Years”. < http://earthquake.usgs.gov/hazards/products/conterminous/
>. Downloaded 07/2016.
Classification
Peak ground acceleration (% gravity) with a 2% likelihood in
50 years was averaged by United States County, and the earthquake hazard of
counties was classified based upon this average.
Low = 0 - 14.25 % gravity peak ground accelerationMedium = 14.26 - 47.5 % gravity peak ground accelerationHigh = 47.5+ % gravity peak ground acceleration
Flood Hazard
United States Federal Emergency Management Administration.
“National Flood Hazard Layer”. 1:10,000. “0.2 Percent Annual Flood Area”. < https://data.femadata.com/FIMA/Risk_MAP/NFHL/
>. Downloaded 07/2016.
Classification
The National Flood Hazard Layer 0.2 Percent Annual Flood
Area was spatially intersected with the United States Counties layer, splitting
flood areas by county and adding county information to flood areas. Flood area
was aggregated by county, expressed as a fraction of the total county land
area, and flood hazard was classified based upon percentage of land that is
susceptible to flooding. National Flood Hazard Layer does not cover the entire
United States; coverage is focused on populated areas. Areas not included in
National Flood Hazard Layer were assigned flood risk of Low in order to include
these areas in further analysis.
Low = 0-.001% area susceptibleMedium = .00101 % - .005 % area susceptibleHigh = .00501+ % area susceptible
Heat Wave Hazard
United States Center for Disease Control and Prevention.
“National Climate Assessment”. Contiguous United States Counties. “Extreme Heat
Events: Heat Wave Days in May - September for years 1981-2010”. Downloaded
06/2016.
Classification
Heat wave was classified by dividing counties based upon the
number of heat wave days they experienced over the 30 year time period described
in the dataset.
Low = 126 - 171 Heat wave DaysMedium = 172 – 187 Heat wave DaysHigh = 188 – 255 Heat wave Days
Hurricane Hazard
National Oceanic and Atmospheric Administration. Coastal
Services Center. “Historical North Atlantic Tropical Cyclone Tracks, 1851-2004”.
1: 2,000,000. < https://catalog.data.gov/dataset/historical-north-atlantic-tropical-cyclone-tracks-1851-2004-direct-download
>. Downloaded 06/2016.
National Oceanic and Atmospheric Administration. Coastal
Services Center. “Historical North Pacific Tropical Cyclone Tracks, 1851-2004”.
1: 2,000,000. < https://catalog.data.gov/dataset/historical-north-atlantic-tropical-cyclone-tracks-1851-2004-direct-download
>. Downloaded 06/2016.
Classification
Atlantic and Pacific datasets were merged. Tropical storm
and disturbance tracks were filtered out leaving hurricane tracks. Each
hurricane track was assigned the value of the category number that describes
that event. Weighting each event by intensity ensures that areas with higher
intensity events are characterized as being more hazardous. Values describing each
hurricane event were aggregated by United States County, normalized by total
county area, and the hurricane hazard of counties was classified based upon the
normalized value.
Landslide Hazard
United States Geological Survey. “Landslide Overview Map of
the United States”. 1:4,000,000. “Landslide Incidence and Susceptibility in the
Conterminous United States”. <
https://catalog.data.gov/dataset/landslide-incidence-and-susceptibility-in-the-conterminous-united-states-direct-download
>. Downloaded 07/2016.
Classification
The classifications of High, Moderate, and Low landslide
susceptibility and incidence from the study were numerically coded, the average
value was computed for each county, and the landslide hazard was classified based
upon the average value.
Long-Term Drought
Hazard
United States Drought Monitor, Drought Mitigation Center,
United States Department of Agriculture, National Oceanic and Atmospheric
Administration. “Drought Monitor Summary Map”. “Long-Term Drought Impact”. <
http://droughtmonitor.unl.edu/MapsAndData/GISData.aspx >. Downloaded
06/2016.
Classification
Short-term drought areas were filtered from the data;
leaving only long-term drought areas. United States Counties were assigned the
average U.S. Drought Monitor Classification Scheme Drought Severity Classification
value that characterizes the county area. County long-term drought hazard was
classified based upon average Drought Severity Classification value.
Low = 1 – 1.75 average Drought Severity Classification valueMedium = 1.76 -3.0 average Drought Severity Classification
valueHigh = 3.0+ average Drought Severity Classification value
Snowfall Hazard
United States National Oceanic and Atmospheric
Administration. “1981-2010 U.S. Climate Normals”. 1: 2,000,000. “Annual Snow
Normal”. < http://www1.ncdc.noaa.gov/pub/data/normals/1981-2010/products/precipitation/
>. Downloaded 08/2016.
Classification
Average yearly snowfall was joined with point location of
weather measurement stations, and stations without valid snowfall measurements
were filtered out (leaving 6233 stations). Snowfall was interpolated using
least squared distance interpolation to create a .05 degree raster describing
an estimate of yearly snowfall for the United States. The average yearly
snowfall raster was aggregated by county to yield the average yearly snowfall
per United States County. The snowfall risk of counties was classified by
average snowfall.
None = 0 inchesLow = .01- 10 inchesMedium = 10.01- 50 inchesHigh = 50.01+ inches
Tornado Hazard
United States National Oceanic and Atmospheric
Administration Storm Prediction Center. “Severe Thunderstorm Database and Storm
Data Publication”. 1: 2,000,000. “United States Tornado Touchdown Points
1950-2004”. < https://catalog.data.gov/dataset/united-states-tornado-touchdown-points-1950-2004-direct-download
>. Downloaded 07/2016.
Classification
Each tornado touchdown point was assigned the value of the
Fujita Scale that describes that event. Weighting each event by intensity
ensures that areas with higher intensity events are characterized as more
hazardous. Values describing each tornado event were aggregated by United
States County, normalized by total county area, and the tornado hazard of
counties was classified based upon the normalized value.
Volcano Hazard
Smithsonian Institution National Volcanism Program.
“Volcanoes of the World”. “Holocene Volcanoes”. < http://volcano.si.edu/search_volcano.cfm
>. Downloaded 07/2016.
Classification
Volcano coordinate locations from spreadsheet were mapped
and aggregated by United States County. Volcano count was normalized by county
area, and the volcano hazard of counties was classified based upon the number
of volcanoes present per unit area.
None = 0 volcanoes/100 kilometersLow = 0.000915 - 0.007611 volcanoes / 100 kilometersMedium = 0.007612 - 0.018376 volcanoes / 100 kilometersHigh = 0.018377- 0.150538 volcanoes / 100 kilometers
Wildfire Hazard
United States Department of Agriculture, Forest Service,
Fire, Fuel, and Smoke Science Program. “Classified 2014 Wildfire Hazard
Potential”. 270 meters. < http://www.firelab.org/document/classified-2014-whp-gis-data-and-maps
>. Downloaded 06/2016.
Classification
The classifications of Very High, High, Moderate, Low, Very
Low, and Non-Burnable/Water wildfire hazard from the study were numerically
coded, the average value was computed for each county, and the wildfire hazard
was classified based upon the average value.