Summary
It is found that under arid zone conditions, the evaporation by U.S.A. open pan evaporimeter is much higher than the potential evaporation obtained by Pennan's method. In order to represent the observed values of evaporation better, a new prediction equation [Eq. (4)] was obtained in terms of the same variables as in Penman's equation viz. aerodynamic term and energy balance term. The multiple correlation coefficient is 0.9823. It is found from the equation that the weightages for aerodynamic and energy balance terms are 0.61 and 1.13, while as per Penman's equation, the weightages for these terms are 1 and 4 respectively thereby showing that under estimation by Perman's method is due to low weightage given to the aerodynamic term which, under arid zone conditions, is not only numerically higher but also is more important in determining evaporation.
Zusammenfassung
Unter den Bedingungen der ariden Zone sind die mit der US-Verdunstungswanne gemessenen Verdunstungswerte viel größer als die nach der Methode von Penman berechnete potentielle Verdunstung. Zur besseren Angleichung an die beobachteten Verdunstungswerte wird eine neue Gleichung [Gl. (4)] abgeleitet, die die gleichen Terme wie Penmans Formel enthält, nämlich einen aerodynamischen Term und einen Energiebilanzterm. Der multiple Korrelationskoeffizient beträgt 0,9823. Es wurde festgestellt, daß in Gl. (4) die Gewichte von aerodynamischen und Energiebilanzterm im Verhältnis 0,61 zu 1,13 stehen, während sie in Penmans Gleichung sich wie 1 zu 4 verhalten. Daraus ergibt sich, daß in Penmans Formel der aerodynamische Term für die aride Zone unterbewertet ist.
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Krishnan, A., Kushwaha, R.S. A critical study of evaporation by Penman's method during the growing season of vegetation in the arid Zone of India. Arch. Met. Geoph. Biokl. B. 19, 267–276 (1971). https://doi.org/10.1007/BF02253553
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DOI: https://doi.org/10.1007/BF02253553