The Role of Evapotranspiration Models in Irrigation Scheduling

Jensen, Marvin E. and Wright, James L. (1978) The Role of Evapotranspiration Models in Irrigation Scheduling. Transaction of the ASAE. 21(1):82-87.

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Abstract

MOST evapotranspiration (El) models are based
on physical principles controlling evaporation and
the conservation of mass and energy, and use daily
climatic data. ET models coupled with irrigation models
are valuable tools because they enable trained and experienced
irrigation specialists to provide irrigation
scheduling services at a reasonable cost.

Estimated standard deviations of mean daily ET
for 1- to 30-day periods (S-et) at Akron, Colorado;
Davis, California; Kimberly, Idaho; and Lompoc,
CA varied from 0.9 to 1.3 mm/day. S-et decreased
to 0.4 to 0.7 mm/day for 15- to 30-day periods.

Standard errors of. ET estimates (Sy,x) with a combination
equation based on 243 days of data from
Kimberly, ID were normally distributed. The Sy,x for
daily values was 1.0 mm/day. The Sy,x decreased inversely
with the square root of the number of days for
up to 30 days and was similar to those reported for other
areas using models that operate on daily climatic data.

A summary of factors affecting confidence levels in
irrigation scheduling is presented along with the expected
standard deviations. Generally, the error in estimating
irrigation applications exceeds estimated ET
errors. The error in measuring soil moisture is generally
smaller than estimated ET and irrigation application
errors.

Item Type:	Article
NWISRL Publication Number:	0391
Subjects:	Irrigation > Irrigation scheduling Water > Evapotranspiration Research methodology Mass Import - autoclassified (may be erroneous)
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:51
Last Modified:	02 Feb 2017 22:30
Item ID:	330
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/330