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

Daymet is a model algorithm. Required model inputs include a digital elevation model, derived horizon files, a land water mask, and observations of daily maximum temperature, minimum temperature, and precipitation from ground-based meteorological stations. One file per year for each year of station data is assembled and input into the Daymet model algorithm.

Required model inputs include a digital elevation model, derived horizon files, a land water mask, and observations of daily maximum temperature, minimum temperature, and precipitation from ground-based meteorological stations. For Daymet version 3 processing, surface observations were available from the Global Historical Climatology Network (GHCN)-Daily dataset distributed by the National Centers for Environmental Information (NCEI) (Menne et al., 2012). One file per year for each year of station data is assembled and input into the Daymet model algorithm.

A Daymet dataset product is available for the the station-level daily weather observation data and the corresponding Daymet model predicted data for the three model parameters: tmin, tmax, and prcp. Also included are corresponding station metadata files for each variable and year, including the station name, station identification, latitude, and longitude.

The Daymet algorithm manages the large number of input data and large spatial extent of the study area by creating a system of 2 degree x 2 degree tiles that are processed individually through the Daymet software. These tiles are identified by a TileID that is derived within the Daymet algorithm and is consistent throughout the temporal period of the Daymet record.

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.

Annual Climate Summaries on a 1-km Grid for North America, Version 4 R1

Filename format: daymet_v4_<pppp>_ann<xxx>_<region>_<yyyy>.<ext>, where:

<pppp> is the respective parameter abbreviation (prcp, swe, tmax, tmin, and vp),
<xxx> is the summary, either 'avg' (average) or 'ttl' (total),
<region> is either 'na' (for continental North America), 'hi' (for hawaii), or 'pr' (for Puerto Rico),
<yyyy> is year (1950 through 2023), and
<ext> is file format extension, either 'nc' (netCDF) or 'tif' (Cloud-Optimized GeoTIFF)

Example filename: daymet_v4_tmax_annavg_na_2014.nc

Daily Surface Weather Data on a 1-km Grid for North America, Version 4 R1

Filename format: daymet_v4_daily_<region>_<pppp>_<yyyy>.nc, where:

<region> is either 'na' (for continental North America), 'hi' (for hawaii), or 'pr' (for Puerto Rico),
<pppp> is the respective parameter abbreviation (dayl, prcp, srad, swe, tmax, tmin, and vp), and
<yyyy> is year (1950 through 2023).

Example filename: daymet_v4_daily_na_prcp_2014.nc

Sub-daily Climate Forcings for Puerto Rico

The file naming convention is clmforce.Daymet4_<reanalysis_ds>_PR.1km.<var>.<yyyy-mm>.nc, where:

<reanalysis_ds> = the meteorological reanalysis dataset 'GSWP3' or 'NARR'
<var> = the file variable(s) desription abbreviation ('Prec', 'Solr', 'TPQWL')
<yyyy-mm> = the year-month date range of the file

Example filename: clmforc.Daymet4_GSWP3_PR.1km.Prec.1950-01.nc

Daymet Version 4 Monthly Latency: Daily Surface Weather Data

Filename format: daymet_v4ll_daily_<region>_<pppp>_<yyyy><mm>.nc, where:

<region> 'na' (continental North America), 'pr' (Puerto Rico), 'hi' (Hawaii)
<pppp> is the respective parameter abbreviation (dayl, prcp, srad, swe, tmax, tmin, and vp),
<yyyy><mm> is year and month

Example filename: daymet_v4ll_daily_na_tmax_202101.nc

Monthly Climate Summaries on a 1-km Grid for North America, Version 4 R1

Filename format: daymet_v4_<pppp>_mon<xxx>_<region>_<yyyy>.<ext>, where:

<pppp> is the respective parameter abbreviation (prcp, swe, tmax, tmin, and vp),
<xxx> is the summary, either 'avg' (average) or 'ttl' (total),
<region> is either 'na' (for continental North America), 'hi' (for hawaii), or 'pr' (for Puerto Rico),
<yyyy> is year (1950 through 2022), and
<ext> is file format extension, either 'nc' (netCDF) or 'tif' (Cloud-Optimized GeoTIFF)

Example filename: daymet_v4_tmin_monavg_na_1988.nc

Station-Level Inputs and Cross-Validation for North America, Version 4 R1

Filename format: daymet_v4_stnxval_<pppp>_<region>_<yyyy>.nc, where:

<pppp> is the respective meteorological variable (tmax, tmin, and prcp)
<region> is 'na' (for continental North America), 'hi' (for Hawaii), or 'pr' (for Puerto Rico), and
<yyyy> is year (1950 through 2022)

For ORNL DAAC distribution, Daymet binary outputs are converted to a spatially referenced, gridded, netCDF file format that follow netCDF Climate and Forecast (CF) Metadata conventions. The CF standard provides a description of each data variable represented, and the spatial and temporal properties of each 2-degree tile. By providing data in this format, users have a robust means to locate data in both space and time as well as a number of software options for their own research needs. Daily gridded surface data for each of the 7 variables are listed below. The ORNL DAAC also mosaics the 2-degree tiles into a seamless gridded netCDF file of daily data for each variable and each year. These mosaic files, and other pre-derived data products, are available for download through the ORNL DAAC.

Parameters, Parameter abbreviations, Units, and Descriptions

Parameter	Abbr	Units	Description
Day length	dayl	s/day	Duration 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
Precipitation	prcp	mm/day	Daily total precipitation in millimeters per day, sum of all forms converted to water-equivalent. Precipitation occurrence on any given day may be ascertained.
Shortwave radiation	srad	W/m2	Incident 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 equivalent	swe	kg/m2	Snow water equivalent in kilograms per square meter. The amount of water contained within the snowpack.
Maximum air temperature	tmax	degrees C	Daily maximum 2-meter air temperature in degrees Celsius.
Minimum air temperature	tmin	degrees C	Daily minimum 2-meter air temperature in degrees Celsius.
Water vapor pressure	vp	Pa	Water vapor pressure in pascals. Daily average partial pressure of water vapor.

Image Quality

Spatial Resolution: 1 km x 1 km

Temporal Resolution: Daily

Years Available:

North America, Hawaii: 1980 to present
Puerto Rico: 1950 to present (Puerto Rico data prior to 1980 are not available through the Single Pixel Extraction Tool)

The North American Daymet projection system and parameters:

Projection System: Lambert Conformal Conic
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 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.

Daymet 2 degree x 2 degree distribution grid.