3.1 etp_jen.aml

This AML allows the calculation of the potential evapotranspiration based on the empirical equation of Jensen and Haise (1963). This equation was specifically optimized for the arid Intermountain West. The method is based on monthly mean values for daily solar radiation and temperature (it, thus, can be applied to any time period on the basis of daily values):
 


where: ETp = monthly mean of daily potential evapotranspiration (mm/day); Rs = monthly mean of daily global (total) solar radiation (kJ/m2/day); Ta = monthly mean of daily air temperature (°C). Comparative calculations based on the Solar Thermal Unit method (Caprio, 1974) and the Turc method (Turc, 1963), both based on the same independent parameters, reveal very similar results.
 

Modifications:

  • The formula displayed here is updated as of Sept. 7th 2003 thanks to Yuanhong Zhu, who reported this bug. The AML code however was correct and didn't need adjustments.
     
     
     

    General specifications of the AML:

    Command: &r  etp_jen     (at GRID prompt)
    Required input: Grids of avg. temperature, and of global radiation
    Output units: 1/10 mm/day
    Speed of calculations: Fast due to optimized programming
    Flexibility of the routine: High; user can adjust AML at interface
    User interface: Limited, but simple and easy
    Known errors:  -
    Programmer N.E. Zimmermann
    Download: etp_jen.aml       (use: "save link as")
    Contact: niklaus.zimmermann @ wsl.ch

     

    References:

    Caprio, J.M., 1974. The Solar Thermal Unit Concept in Problems Related to Plant Development and Potential Evapotranspiration. In: H. Lieth (Editor), Phenology and Seasonality Modeling. Ecological Studies. Springer Verlag, New York, pp. 353-364.

    Jensen, M.E. and Haise, H.R., 1963. Estimating evapotranspiration from solar radiation. J. Irrig. Drainage Div. ASCE, 89: 15-41.

    Turc, L., 1963. Evaluation des besoins en eau d'irrigation, évapotranspiration potentielle, formulation simplifié et mise à jour. Ann. Agron., 12: 13-49.
     
     

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    Last Updated: 10/07/03
    By Niklaus E. Zimmermann