Water balance and Its Long-term Changes in the Warm Half-year

Water balance shows the difference between rainfall amount and the potential evapotranspiration intensity. Positive balance means predominant rainfall and water surplus. Negative balance, in contrast, means predominant evaporation and water insufficiency. Two smaller maps show the total water balance for two 30-year periods. It can be seen that the period 1991-2020 has a lower value of water balance, i. e., less water available in landscape. The difference between the two maps in the top right corner is represented by the large map, where areas with lower water balance represented by hues of red color dominate. In the long term, the most negative water balance is observed in south Moravia and, to a certain extent, also in central Bohemia and Ústecký region. The most profound decrease over the 30 years can be observed in the northern part of the country. In contrast, a positive difference is only very rare in some parts in the most western tip of the Czech Republic and the northern part of the Olomoucký region. The total average water balance for the individual half-years is shown on the bar chart in the top left corner, and the average water balance for the individual decades is shown on the bar chart below. One can see a clear decreasing trend, and the last decade (2011-2020) is one with the most negative total, primarily due to the very dry years 2015, 2018, and 2019. Only 10 out of the total 60 summers showed a positive water balance.