Till the late 90-ties of the XXth century the Penman method has been used widely to evaluate the reference evapotranspiration. The ongoing research verified the Penman method and convinced many scientists to look for the modification of his formula, because the calculated values of reference evapotranspiration were too high. Nowadays, the method most frequently used is that of Penman-Monteith. It enables the more accurate evaluation of the atmospheric evaporation ability, therefore it is preferred for the calculation of climatic water balance or drought references. Many modifications of Penman-Monteith method can be found in literature. The authors have analyzed the data from four various regions of Poland and have presented the differences in values of reference evapotranspiration depending on the method of calculation. ...
The paper presents an application to calculate the daily reference evapotranspiration values (ETo), understood as the amount of evaporation from the lawn surface fully developed, growing on the soil, which provides optimal growth conditions. The presented application allows to determine the ETo value for any location for given geographic coordinates and location above sea level on the basis of daily values of air temperature, saturation deficit, wind speed and relative sunshine. As the input data there are also variables such as psychometric constant dependent on the location above sea level and atmospheric pressure, the maximum vapor pressure and the slope vapor pressure deficit dependent on temperature, extraterrestrial radiation dependent on sequent day number of the year, which in Evapo application are determined automatically based on given geographical information. The application allows to analyze evapotranspiration variability during particular years and months. Basing on 30 years of meteorological data the values of evapotranspiration for the Vancouver and Wrocław - Swojec was calculated and exemplary analysis was performed using the presented application. ...
