What Will Climate Change Mean to Your Community?

The Snapshot Tool describes some select climate-health vulnerabilities found in the U.S. Here is how we developed them, from among the measures available in each category:

Extreme Heat

We classified counties as highly vulnerable to extreme heat if there were on average more summer days of extreme heat in 2000-2009 than would be expected based on historical patterns (1961-1990 reference period) We define extreme heat days as days with daily maximum temperatures above the 90th percentile June-July-August temperature from the 1961-1990 reference period. Therefore, counties with more than 9 days of extreme heat (9/90 = 10th percentile) were considered vulnerable and assigned a 1; otherwise counties were assigned a 0 for “not extreme heat” (or -9 for “insufficient monitoring data to track extreme heat”). More information can be found at http://www.nrdc.org/health/climate/heat.asp.

Air Quality

We classified counties as highly vulnerable to poor air quality if any part of the county had both ragweed present, and at least 1 day per year on which ozone concentrations were higher than (i.e. exceeded) EPA’s health-based for ozone air quality (during 2002-2006). We selected areas that met both of these criteria and assigned a 1 to the county if any part of the county fell within the ragweed and ozone ‘exceedance’ zone. Otherwise counties were assigned a 0. More information can be found at http://www.nrdc.org/health/climate/airpollution.asp.

Flooding

Data was originally gathered on the watershed level, so we classified counties as highly vulnerable to flooding if there were part of a watershed region with more days per year with extreme high flow than was expected based on historical patterns. Extreme high flow days are defined as the average number of days annually (2000-2009) that are above the 95th percentile relative to a 1961-1990 reference period. We calculated the percentage of each county’s surface area in a particular watershed to weight the number of extreme high flow days in each county. So for example, if 25% of County A is located in a watershed with 20 extreme high flow days and 75% of County A is located in a watershed with 10 extreme high flow days, the total number of extreme high flow days in County A is 0.25 x 20 +0.75 x 10 = 12.5. Counties with more than 18 days of extreme high flow (18/365= 5th percentile) were assigned a 1; otherwise counties were assigned a 0. More information can be found at http://www.nrdc.org/health/climate/floods.asp.

Drought

Data was originally gathered on the watershed level, so we classified counties as highly vulnerable to drought if there were part of a watershed region with more per year with extreme low flow than was expected based on historical patterns. Extreme low flow days are defined as the average number of days annually (2000-2009) that are below the 5th percentile relative to a 1961-1990 reference period. We calculated the percentage of each county’s surface area in a particular watershed and weighted the number of extreme low flow days by the county’s surface area ¬percentage, in the same fashion as with flooding above. Counties with more than 18 days of extreme low flow (18/365 = 5th percentile) were assigned a 1; otherwise counties were assigned a 0. More information can be found at http://www.nrdc.org/health/climate/drought.asp.

Dengue Fever

We classified counties as highly vulnerable to dengue fever if the county reported positive for one or both dengue mosquito vector species (as of 2005) and had more than 1 reported case in the state. We selected counties that met both of these criteria and assigned a 1, otherwise counties were assigned a 0. More information can be found at http://www.nrdc.org/health/climate/disease.asp.

Wildfires

We classified counties as highly vulnerable to wildfire if there was at least one large wildfire (greater than 90 acres) since 2006 within the county, or within 10 miles of the county (data from 2006-2012). Fires were filtered to those greater than 90 acres and merged into a single ‘shapefile’ that was used to create the map. The shapefile was buffered by 10 miles, and then intersected with the county layer. If any or all of a county experienced a wildfire the county was assigned a 1, otherwise counties were assigned a 0. More information can be found at http://www.nrdc.org/health/extremeweather/.

Sea Level Rise

We classified counties as highly vulnerable to sea level rise if they were a coastal county. Those counties that intersected with the U.S. coastline were assigned a 1; otherwise counties were assigned a 0.

Extreme Weather

We classified counties as highly vulnerable to extreme weather if there was at least 1 monthly record-breaking event of each type – heat, rain, and snow - in 2011 and 2012 combined. We combined 2011 and 2012 data and totaled the number of monthly high maximum temperature, high minimum temperature, high rainfall and high snowfall records broken. Counties were assigned the total number of record breaking events. More information can be found at http://www.nrdc.org/health/extremeweather/.