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vol. 13, nr. 2 (2009)
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Comparison of the Penman and Penman-Monteith methods by means of probability distributions of reference evapotranspiration
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Edward G±siorek, Joanna Kamińska, Elæbieta Musia³
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Department of Mathematics, Wroc³aw University of Environmental and Life Sciences ul. Grunwaldzka 53, 50-357 Wroc³aw |
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vol. 13 (2009), nr. 2,
pp. 341-351
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abstract:
Till the late 90-ties of the 20th century the Penman method had been used widely to evaluate the reference evapotranspiration. Nowadays, the most frequently used method is that of Penman-Monteith, modified by Allen and co-authors. A new modification of the Penman-Monteith method, verified by many researchers worldwide and in different regions of Poland, enables more accurate evaluation of the atmospheric evaporation ability, therefore it is preferred. In this study, data from stations in Bydgoszcz (1945-2003), £ód¼ (1954-1995) and Wroc³aw (1964-2000) were analysed. The sums of reference evapotranspiration in the growing season, calculated by means of the Penman and Penman-Monteith methods, were fitted to the function of probability distribution. The verification of hypothesis on consistency of empirical distribution to gamma distribution was performed using the Chi square test. Then, by means of gamma distribution, the growing seasons in the examined regions and multi-year periods were classified as: wet, medium wet, dry and very dry. In the above mentioned seasons, the results obtained by the use of Penman and Penman-Monteith methods were compared. Those comparisons revealed that the values of reference evapotranspira-tion, calculated by the Penman method, are overestimated in the selected regions.
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keywords:
reference evapotranspiration, gamma distribution
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original in:
Polish
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