# Informations et ressources scientifiques sur le développement des zones arides et semi-arides

Accueil du site Projets de développement Projets de recherche pour le Développement 2012 REFERENCE EVAPOTRANSPIRATION DETERMINATION USING THE RECURSIVE METHOD AND SURFACE AERODYNAMIC TEMPERATURE

## Evapotranspiration Détemination

United States Department of Agriculture (USDA) Research, Education & Economics Information System (REEIS)

Titre : REFERENCE EVAPOTRANSPIRATION DETERMINATION USING THE RECURSIVE METHOD AND SURFACE AERODYNAMIC TEMPERATURE

Identification : COL00602A

Pays : Etats Unis

Durée : Jul 1, 2012 à Jun 30, 2015

Domaine : water conservation, crop water use, reference et, evapotranspiration,alfalfa et, irrigation management, crop coefficient, recursive method, aerodynamic temperature

Partenaire : COLORADO STATE UNIVERSITY FORT COLLINS,CO 80523

Objectifs
Accurate calculation of crop evapotranspiration (ET) is very important in properly determining the correct amounts and timing of irrigation in order to sustain and improve food production in an environment of climate change and population growth. The use of the ASCE-EWRI 2005 Standardized Penman-Monteith (PM) equation to calculate ET by using crop coefficients (Kc) and reference ET (ETr) values is being highly encouraged by the agricultural water management community in the U.S. However, the method has been shown to deviate from actual measurements of grass and alfalfa reference ET, especially in arid and semi-arid climates. One of the reasons for the deviation may be the omission of the surface temperature (Ts) from the PM equation. The recursive method calculates ETr making no assumptions regarding the temperature and the saturation humidity at the evaporating surface and solves iteratively for Ts. The aerodynamic temperature (To) has been shown to be the appropriate air temperature for computing sensible heat flux in the energy balance (EB) equation. Therefore, it is hypothesized that by using the To in conjunction with the recursive method a very accurate computation of ETr would be possible under different conditions. This project is designed to evaluate the applicability of a ET recursive method by itself and in conjunction with To, to improve the computation of alfalfa ETr and Kcs in Colorado (CO). The specific objectives are : 1) to apply the ASCE-EWRI 2005 standardized reference ET equation to an irrigated alfalfa field, 2) to apply the recursive method, developed by Budyko (1956), to an irrigated alfalfa field, 3) to measure aerodynamic temperature using three independent instruments (an eddy covariance system, a large aperture scintillometer, and an aerodynamic profile tower), 4) to use measured aerodynamic temperature in the recursive method applied to an irrigated alfalfa field, 5) to evaluate the ET values obtained from objectives 1, 2 and 4 using measured ET values from a precision weighing lysimeter in CO. Results will indicate whether the methodology to calculate ETr needs to be changed in CO. Adopting the new method in CO will improve the computation of ETr and Kcs and hence will promote a better agricultural water management in the state. The investigators of this research will write peer-reviewed Journal articles and Extension factsheets to disseminate the findings. Presentations will be delivered to the state engineer office to promote the adoption of the methodology in CO. In addition, research results will be presented to the state climatologist that oversees the management of the COlorado AGricultural Meteorological nETwork (COAGMET) to encourage the adoption of the new methodology through the reporting of ETr calculations on COAGMET’s webpage. Further publication of research results can be pursued through the Colorado Water Institute Newsletter and the Colorado Agricultural Experiment Station (CAES). Irrigation districts, water consultants, state engineers, and federal researchers in the state are expected to adopt the procedure and improve water management in the state.

Présentation : USDA

Page publiée le 7 novembre 2015, mise à jour le 14 novembre 2017