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Hydraulics and Hydrology
AGNPS - Climate Data Generation
agGEM and preGEM
If the location of interest is near enough to one of the 233 US stations for which statistical parameter
files have already been developed, the user may employ agGEM to produce an AnnAGNPS climate file. The
agGEM executable may be downloaded below. The link "already developed statistical parameter files"
presents all 233 stations and any of those downloadable files are valid input files for agGEM.
Two files
are created as output from agGEM. One is the standard GEM6 output, with max, min, and dewpoint temperatures
in degrees Fahrenheit, precipitation in inches, wind speed in meters per second, and solar radiation in
Langleys. The other output file is in the format of an AnnAGNPS climate file and is immediately ready for
input to AnnAGNPS. The user may choose either SI or English units for that file. The output then, for SI
units, is degrees celsius for the temperatures, millimeters for precipitation, meters per second for wind
speed, and Watts per square meter for solar radiation. In English units, the output is degrees Fahrenheit
for the temperatures, inches for precipitation, miles per hour for wind speed, and BTUs per hour per square
foot for solar radiation.
If the user wishes to develop input files to agGEM for a location other than these 233 stations, an
adequate historical record of the six datatypes must exist. Although preGEM will work for any number
of years of historic data, it is generally agreed by climate statisticians that for a record less than
twenty years the output may be suspect. In addition, there must be no missing data. Whether the output
remains statistically valid enough with the inclusion of estimated data is up to the user to decide.
The units for the six datatypes required to run preGEM are degrees Fahrenheit for the temperatures,
inches for precipitation, meters per second for wind speed, and Langleys for solar radiation.
Downloads:
AGNPS climate input file data format template
preGEM
preGEM input template
agGEM
already developed statistical parameter files
Contact:
Dan Moore.
Details about preGEM
The program requires an input file of historical data in the following format. (Data columns are not of fixed format —
simply separate by spaces. This is a text file, which may have a .txt or any other extention.)
34 22.2022 159.4492 345 Princeville
Mon Day Year Prec tmax tmin dewp solar wind
1 1 1949 0.00 81 69 68 320.95 4.11
1 2 1949 0.00 77 71 68 219.94 4.34
1 3 1949 1.54 77 64 64 343.97 5.64
1 4 1949 0.01 73 69 60 409.61 6.15
etc.
A template in Excel may be downloaded above. The first line data is:
number of years of data in the file, latitude, longitude, elevation, and sitename.
The program has no restriction on the number of years of data. However, a
dataset of at least 20 years is preferred, as statistical reliability declines
rapidly with fewer. In addition, there can be no missing data. Any missing data
in the historic record must be estimated before running preGEM. The input data
units should be Fahrenheit for temperatures, inches for precip, Langleys for
solar, and meters per second for wind speed. The output file created is given
the name of the input file with the extension .gm6 which is the extension
expected by the program agGEM. The output of preGEM is input to agGEM.
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