Summary:

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.