The Measured Potential Evaporation in Wrocław and Surface Evaporation Calculated Using the Ivanov Formula (1961–2020)

Abstract

The study shows that the variability of field evaporation sums (Ev) calculated using the Ivanov formula from monthly series of air temperature and relative humidity from the IMWM-PIB Wrocław-Strachowice station relatively accurately reproduces the variability of the potential evaporation values measured in the Agro- and Hydrometeorology Wrocław-Swojec Observatory of the Wrocław University of Environmental and Life Sciences. The largest absolute errors in the estimated monthly Ev values are affected in the period from April to August (±11.7–14.8 mm), and the lowest from November to February (±4.8–10.6 mm). In the cool half-year (October–March), the Ev estimation gives “area-averaged” evaporation values close to reality with an error of about ±24–25 mm, and in the warm half-year (April–September) with an error of ±54–55 mm. In the case of estimated annual evaporation sums, Ivanov’s formula has an average error of about75 mm, which is about 10–12% of this value. The most important factor contributing to the differences between the observed Ev in Wrocław-Swojec and the estimated Ev in Wrocław-Strachowice are the differences in monthly values of relative humidity between these stations (up to 10%). The obtained results allow for the conclusion that the sums of evaporation calculated by Ivanov’s method, especially the annual sums, can be reliably used for various types of hydrological calculations, including the estimation of the climatic water balance in Poland.