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AgriMet The Pacific Northwest Cooperative Agricultural Weather Network

 

About AgriMet Crop Water Use Charts

AgriMet uses site specific weather data to estimate evapotranspiration (ET, or crop water use) for crops grown in the vicinity of each weather station. AgriMet uses the 1982 Kimberly-Penman ET model developed by the USDA Agricultural Research Service in Kimberly, Idaho to compute daily reference ET (ETr)at each station. More information is available about AgriMet's implementation of the Kimberly-Penman Model. AgriMet uses alfalfa as the reference crop, and reference ET is computed from daily (not hourly) weather data.

Crop coefficients are used to compute crop specific ET based on the alfalfa reference ET. These crop coefficients vary throughout the growing season based on the plant growth stage. The crop coefficients are tied to the actual plant growth stage by three dates: Start, Cover, and Terminate dates. Start dates are the beginning of vegetative growth in the spring for perennial crops or the emergence date for row crops. Cover dates are typically when plants reach full foliage. Terminate dates are defined by harvest, frost, or dormancy. See Definitions of Crop Dates for crop specific start, cover, and terminate dates used in the AgriMet program. For more information about crop coefficients, see About AgriMet Crop Coefficients.

Following is an explanation of the columns displayed in an AgriMet crop water use chart:

• Crop: Abbreviated identifier for the crop being modeled. See Key for an explanation of crop codes.
• Start Date: Typically the crop emergence date or beginning of vegetative growth for perennials.
  (Note: 999 is used as a place holder date early in the growing season)
• Daily ET: The previous 4 days of crop specific ET
• Daily Forecast: Average of the last 3 days ET
• Cover Date: Typically when the plant reaches full foliage.
• Term Date: Terminate date (frost, harvest, dormancy, etc.)
• Sum ET: Total crop water use to date by crop, since the start date.
• 7 Day Use: Total crop water use for the last 7 days.
• 14 Day Use: Total crop water use for the last 14 days.

AgriMet crop water use charts are updated each morning at approximately 5:30 am Mountain Time, and reflect ET based on the weather conditions for the previous day. There is also a tabular ET Summary Table showing daily crop water use for each crop for the entire growing season. These are available for both current and previous years. A table of Evapotranspiration Totals and Averages provides yearly totals and long term averages of crop specific ET. A table of Month Average Reference Evapotranspiration provides period of record monthly ETr values for each weather station.