Ref-ET
Soil Water Management
Evapotranspiration and Irrigation Water Requirments
Mid Snake Water Quality

 

 

 

The following has been superceeded by "Evapotranspiration and Consumptive Irrigation Requirements for Idaho" by R. G. Allen and C. W. Robison, 2006 (rev 2007). The current information on evapotranspiration and consumptive use in Idaho is located at our ETIdaho web site.

This page provides access to crop evapotranspiration and irrigation water requirement information for various weather stations from Appendix E of the University of Idaho report: "Estimating Consumptive Irrigation Requirements for Crops in Idaho" published in 1983 by R. G. Allen and C. E. Brockway. This report is a Research Technical Completion Report submitted to Idaho Department of Water Resources. Appendix E was not published with the report for general distribution. A copy of Appendix E is on file with IDWR.

The data forms retrieved via this procedure are an inverted copy of the original tables contained within the appendix to be conducive for import into spreadsheets. Additionally, the columns referencing the number of years in the historical record and precipitation are not included, nor are the estimates of the distribution skewness. To retrieve the data, please select a location from the following selection list and press the retrieve button.

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Brief background on the report "Estimating Consumptive
Irrigation Requirements for Crops in Idaho"

R.G. Allen and C.E. Brockway
University of Idaho
August, 1983

The FAO-modifed Blaney-Criddle (FAO-BC) method (Doorenbos and Pruitt, 1977) was used as the basis for the 1983 report for estimating consumptive use on a statewide basis for Idaho, based on accuracy and responsiveness of the equation and the primary data requirement of air temperature, only. The originally grass-based FAO-BC method was converted into an alfalfa-reference method by multiplying by conversion ratios developed using Kimberly lysimeter data and the Kimberly Penman equation. These ratios were found to be transferable to other Idaho sites. Following conversion to an alfalfa reference method, the FAO-BC calculated reference ET was multiplied by alfalfa-based crop coefficients by Wright (1981). These Kc's include impacts of evaporation from wet soil due to irrigation and rainfall.

The FAO-BC method application utilized wind, humidity and solar radiation data from seven regional locations in Idaho. A ten percent upward adjustment to FAO-BC estimates per 1000 meters elevation as suggested by Pruitt (Doorenbos and Pruitt, 1977) was found to be necessary in Idaho and was applied.

NOAA weather stations throughout Idaho were objectively rated according to the degree of station aridity and environmental effects on air temperatures. Mean monthly temperatures at each NOAA site were adjusted downward according to the station aridity rating and maximum aridity effects. Monthly statistics were computed for consumptive use for 98 weather sites in Idaho using the calibrated FAO-BC with elevation correction and alfalfa/FAO-BC reference ratios.

Parameters in the tables are defined as follows:
 

MEAN CU Mean monthly consumptive use over the historical period of record for the station. Units are mm/day for monthly values and mm per season for the growing season period. CU is synonymous with crop evapotranspiration.

MEAN IR

Mean net irrigation requirement for the historical period of record for the station. Units are mm/day for monthly values and mm per season for the growing season period. IR was calculated as IR = CU - Pe where Pe is effective precipitation, calculated in the 1983 study as Pe = 0.7 P. IR must be divided by irrigation efficiency to obtain the gross irrigation water requirement.

STDEV CU

Standard deviation of monthly consumptive use by month or of seasonal consumptive use over the historical period of record for the station. Units are mm/day for monthly values and mm per season for the growing season period.

STDEV IR

Standard deviation of monthly IR by month or of seasonal IR over the historical period of record for the station. Units are mm/day for monthly values and mm per season for the growing season period.