3.2 etp_stu.aml

This AML allows the calculation of the potential evapotranspiration based on the empirical equation of the solar thermal unit concept (Caprio, 1974). This equation was applied to various climate regimes all over the Northern Hemisphere (Caprio, 1974). 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 = mean daily potential evapotranspiration (mm/day); Rs = daily global (total) solar radiation (kJ/m2/day); Ta = mean daily air temperature (°C). Comparative calculations based on the Jensen-Haise method (Jensen and Haise, 1963) and the Turc method (Turc, 1963), both based on the same independent parameters, reveal very similar results.
 
 
 

General specifications of the AML:

Command: &r  etp_stu     (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_stu.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: 9/08/00
By Niklaus E. Zimmermann