Comparison of actual evaporation from water surface measured by GGI-3000 evaporimeter with values calculated by the Penman equation

Abstract

Information about water evaporation is essential for the calculation of water
balance. Evaporation, however, is a very complex physical process and it is therefore
difficult to quantify. Evaporation measurements from the weather station network of the
Czech Hydrometeorological Institute between 1968 and 2011 were performed using the
evaporimeter GGI-3000. Evaporation was calculated using modified standard method
based on FAO. The aim of the article was to compare the measured values and calculations.
It has been found that the evaporation values from water surface calculated
using the empirical equation are usually higher than the measured values by on average
0.8 mm, in extreme cases even 6.9 mm. The measured data shows higher variability than
the calculated values, which means that correlations between series are not strong, the
correlation coefficient being 0.7. Nevertheless the findings can be used for homogenization
of series measured by the GGI-3000 evaporimeter.