Növénytermelés / Volume 64 / Issue 3 (September 2015) / pp. 77-96

VARGA-HASZONIZS Z; TAR K; LANTOS ZS; VARGA Z

Comparison of evapotranspiration calculation methods based on the data of Mosonmagyaróvár

Evapotranspiration is the water transport from different surfaces to the air. It is the most important loss component of the water balance of plants. The functions describing evapotranspiration include methods for calculating potential, equivalent and reference evapotranspiration.

Our study was based on the data measured between 1981–2010 at the meteorological station of Faculty of Agricultural and Food Sciences, University of West Hungary in Mosonmagyaróvár. Measured A-pan values are available since June 1994, so in the case of that parameter only mean values for the 16 years between 1995 and 2010 were used.

In our comparison, the relationships between measured (A-pan) and modelled (Penman method, FAO Penman-Monteith method, Priestley-Taylor method, local formula) evapotranspiration data series were analyzed.

As a result of our investigations, the Penman method and the FAO Penman-Monteith method can be suggested for determining evapotranspiration in Mosonmagyaróvár. The outputs of these models are in good agreement with the measured values and the results of these methods are comparable with domestic and international studies, since these functions are commonly used as reference evapotranspiration throughout the world.

Values of A-pan measurements and local formula changed paralelly with the model values considered as reference evapotranspiration, so these values can be converted to reference evapotranspiration by using a multiplication factor in places where data of wind measurements are not available.

The Priestley-Taylor method gives reliable results only in wet areas, as it includes only the energy required for evapotranspiration, but does not show the effect of the air’s evaporating capacity. As not the whole country is humid, we suppose that the Priestley-Taylor method underestimates the evapotranspiration not only in Mosonmagyaróvár, but also all over Hungary.

If methods for calculating evapotranspiration are compared, it should be considered whether the climatic conditions are relatively homogenous or they show a certain tendency.

Climatic conditions of Mosonmagyaróvár began to change from the 1990s. The average temperature rose, while the relative humidity dropped. Both of them increase evapotranspiration. Since the local formula was based on these two elements, the most significant change was shown in this case. Since relative humidity is only one component of the Penman method and the FAO Penman-Monteith method, these models responded weakly to this change. The Priestley-Taylor method contains no relative humidity component, so it reacted insignificantly to those changes.

Keywords: evapotranspiration, Penman method, FAO-Penman method, Priestley-Taylor method, local formula

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