Analysing the evaporation of Lake Fertő and comparing evaporation calculation methods in the context of climate change

Abstract

As a result of climate change, the factors influencing the water balance of Lake Fertő are also changing, leading to a decrease in the lake’s water resources. Many uncertainties burden the water balance and, thus, future forecasts. The most significant of them arises from the inaccurate determination of evapotranspiration as the primary loss component. Therefore, our research aimed to analyze the uncertainties associated with evaporation. The lake’s evaporation consists of two components: evaporation from the open water surface and transpiration from the reed zones, shaped not only by meteorological factors but also by the physiological processes of the vegetation. Thus, although we are faced with a complex process, in practice, it is still calculated using a very simple procedure, the empirical Meyer formula. In our research, we compared Meyer’s evaporation calculation method with an energy balance-based one over an 11-year-long period (2012-2022). We found that the Meyer method significantly overestimates evaporation, and its climatic forecasting ability is also uncertain, making its use questionable for Lake Fertő. The Meyer formula showed a significant closure error regarding the lake's water balance, averaging -243 mm/year. In contrast, the energy balance-based method resulted in a much smaller one of -56 mm/year. This means that we achieved a significantly better water balance closure when evaporation was determined based on physical principles. As a result, we concluded that for determining the evaporation of Lake Fertő, energy balance-based calculations should be used, as they are more accurate and grounded in physical principles, allowing for verification through measurements.