Skip to main content
image of DAYMET data over North America
image of DAYMET data over North America
image of DAYMET data over North America

Daymet

Daymet uses statistical modeling techniques to provide long-term, continuous, gridded estimates of daily weather and climatology variables from ground-based observations. Daymet data products provide driver data for biogeochemical terrestrial modeling and have myriad applications in many Earth science, natural resource, biodiversity, and agricultural research areas. Daymet weather variables include daily minimum and maximum temperature, precipitation, vapor pressure, shortwave radiation, snow water equivalent, and day length over continental North America, Hawaii, and Puerto Rico.

Partners

DOE

Data Centers

ORNL DAAC

Funding Programs

Terrestrial Ecology Program

Parameters, Parameter Abbreviations, Units, and Descriptions

ParameterAbbrUnitsDescription
Day lengthdayls/dayDuration of the daylight period in seconds per day. This calculation is based on the period of the day during which the sun is above a hypothetical flat horizon
Precipitationprcpmm/dayDaily total precipitation in millimeters per day, sum of all forms converted to water-equivalent. Precipitation occurrence on any given day may be ascertained.
Shortwave radiationsradW/m2Incident shortwave radiation flux density in watts per square meter, taken as an average over the daylight period of the day. NOTE: Daily total radiation (MJ/m2/day) can be calculated as follows: ((srad (W/m2) * dayl (s/day)) / l,000,000)
Snow water equivalentswekg/m2Snow water equivalent in kilograms per square meter. The amount of water contained within the snowpack.
Maximum air temperaturetmaxdegrees CDaily maximum 2-meter air temperature in degrees Celsius.
Minimum air temperaturetmindegrees CDaily minimum 2-meter air temperature in degrees Celsius.
Water vapor pressurevpPaWater vapor pressure in pascals. Daily average partial pressure of water vapor.

The Daymet dataset is stored and distributed as individual CF-Compliant netCDF file for each Daymet variable. The most current Daymet data is being delivered to the user in terms of both Daymet software and Daymet data versions. Version information is recorded in the header file of each of the CF-netCDF files within the Global Attribute fields; Version_software and Version_data. All Daymet data is provisional and subject to revision.

The North American Daymet projection system and parameters:

  • Projection System: Lambert Conformal Conic
  • Parameters:
  • projection units: meters
  • datum (spheroid): WGS_84
  • 1st standard parallel: 25 deg N
  • 2nd standard parallel: 60 deg N
  • Central meridian: -100 deg (W)
  • Latitude of origin: 42.5 deg N
  • false easting: 0
  • false northing: 0

The spatial resolution of the Daymet gridded dataset is 1 km.

The Daymet calendar is based on a standard calendar year. All Daymet years have 1 - 365 days, including leap years. For leap years, the Daymet database includes leap day. Values for December 31 are discarded from leap years to maintain a 365-day year.