The impact of climate change on evaporation from the water surface in Ukraine

Abstract


 
 
 
 Based on the monitoring data, the features of long-term changes of evaporation from the water surface are determined. Data from relatively small evaporators and evaporation basins located in different regions of Ukraine were processed. It was found that during the first part of the observation period, which began in the 1950s, evaporation had the tendency to decrease, while in the second part it increased significantly. To determine the factors of these changes, the existing calculated dependences were analyzed. In most of them, evaporation is determined by three arguments: the partial pressure of saturated water vapour, which corresponds to the water temperature, the actual water vapour pressure, and wind speed. It was determined that the main factor of the modern increase in evaporation is the increase of water temperature, which is accompanied by a significant increase in the partial pressure of saturated water vapour. In particular, the mean water temperature in the Dnipro Reservoirs in May– September during 1977–2020 increased at an average rate of 0.65–0.70 °C per decade, and the air temperature at 0.75 °C per decade. It is important that the relationship between water temperature and the partial pressure of saturated water vapour, which corresponds to it, is nonlinear. Wind speed does not significantly affect evaporation. In addition, in recent decades there has been a tendency to its decrease. An empirical dependence of evaporation on air temperature is proposed. Its nonlinear form indicates a significant increase in evaporation due to the temperature increase. Currently (1991–2020), evaporation from the water surface near Kyiv during the ice-free period is approximately 650 mm, in the south of Ukraine it reaches 1000 mm. The increase in evaporation results in additional water losses and a reduction in available water resources.