Assessment of drought severity in the Czech Republic from 1961 to 2022

Drought monitoring is based on the analysis of a series of drought indicators. Our analysis was carried out using the Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI) with regard to five different time scales (1, 3, 6, 12, and 24 months). One-month indices better capture short-term moisture conditions, while three- and six-month indices describe medium-term conditions, and twelve- and twenty-four-month indices focus on long-term conditions. Potential evapotranspiration was calculated using the Hargreaves-Samani method. Drought was defined as a sequence of months with negative index values. In addition, spatial and temporal variability, frequency, duration, and intensity of drought in the Czech Republic were analyzed during the study period. Furthermore, the distribution of drought in different elevations was also examined.

Remarkable spatial differences were found in the duration and intensity of drought. Generally, the results of the SPEI index assessment showed longer duration and higher intensity of drought compared to the SPI index assessment. Increasing temperatures cause increased evaporation, particularly in the summer season, leading to an increase in events referred to as flash droughts.

The assessment of drought showed the exceptional nature of the period 2014-2020, which peaked in 2018. This applies to both the duration and intensity of drought. This unprecedented drought had a negative impact on the state of forest stands in the Czech Republic, especially spruce stands, which suffered from water stress and were unable to resist bark beetle calamity. Repeated droughts led to accelerated tree mortality. This contribution highlights the importance of the increasing potential of more frequent and more severe drought events in Central Europe.