Details of U.S. Climate Zones

The CBECS climate zones are groups of climate divisions, as defined by the National Oceanic and Atmospheric Administration (NOAA), which are regions within a state that are as climatically homogeneous as possible. Each NOAA climate division is placed into one of five zones based on its 30-year average heating degree-days (HDD) and cooling degree-days (CDD) for the period 1971 through 2000. (These climate zones have been updated for the 2003 CBECS. All previous CBECS used averages for the 45-year period from 1931 through 1975.)

A HDD is a measure of how cold a location was over a period of time, relative to a base temperature (in CBECS, 65 degrees Fahrenheit). The heating degree-day is the difference between that day’s average temperature and 65 degrees if the daily average is less than 65; it is zero if the daily average temperature is greater than or equal to 65. For example, if the average temperature for a given day is 40 degrees, then the heating degree-days for that single day equal 25. Heating degree-days for a year are the sum of the daily heating degree-days that year.

Similarly, a CDD is a measure of how hot a location was over a period of time, relative to a base temperature (65 degrees Fahrenheit). The cooling degree-day is the difference between that day’s average temperature and 65 degrees if the daily average is greater than 65; it is zero if the daily average temperature is less than or equal to 65. For example, if the average temperature for a given day is 80 degrees, then the cooling degree-days for that single day equal 15. Cooling degree-days for a year are the sum of the daily cooling degree-days for that year.

There are 359 NOAA climate divisions within the 50 U.S. states. Boundaries of these divisions generally coincide with county boundaries, except in the western U.S., where they are based largely on drainage basins. For a map of all the NOAA climate divisions in the U.S., see www.cdc.noaa.gov/usclimate/map.html.

To help determine the NOAA climate division for your city (if it is not obvious from the map), there is a file containing a list of climate divisions by county (county.dat) which is accessed from www.cdc.noaa.gov/usclimate/boundaries.html.

Each building in the CBECS is assigned a CBECS climate zone based on the 30-year average (1971-2000) HDD and CDD (base 65 degrees Fahrenheit) for the NOAA climate division in which the weather station closest to the sampled building is located. The ranges of HDD and CDD used to determine climate zones are:

Return to Climate Zone Map

Return to CBECS Home Page

Contacts

Specific questions on this product may be directed to:

Joelle Michaels

joelle.michaels@eia.doe.gov

CBECS Manager

Phone: (202) 586-8952

FAX: (202) 586-0018