American Society of Civil Engineers

Rational Use of the FAO Blaney-Criddle Formula

by Richard G. Allen, (Asst. Prof., Utah State Univ., Dept. of Agr. and Irrigation Engrg., Logan, UT 84321) and William O. Pruitt, M.ASCE, (Agr. Engr., Univ. of California, Davis, CA 95616)

Journal of Irrigation and Drainage Engineering, Vol. 112, No. 2, May 1986, pp. 139-155, (doi:

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Document type: Journal Paper
Discussion: by George H. Hargreaves    (See full record)
Closure:(See full record)
Abstract: The FAO Blaney-Criddle (FAO-BC) evapotranspiration equation was calibrated and tested against a Penman combination equation with local wind function and daily lysimeter measurements of alfalfa evapotranspiration. Agreement between the calibrated FAO-BC method and lysimeters was excellent for daily, weekly and monthly estimates when measured values for solar radiation, air temperature, relative humidity and wind speed were used. An elevation correction reduced scatter in estimates among Idaho locations. Statistics describing the daily Penman and FAO-BC estimates deviated from those calculated for measured alfalfa reference evapotranspiration. Air temperature and relative humidity data for nonagricultural weather stations were adjusted according to fetch and aridity before being used to estimate consumptive use requirements throughout Idaho. Calibration of the FAO-BC allowed use of alfalfa-based crop coefficients.

ASCE Subject Headings:
Data analysis
Water use
Weather conditions