Temperature extremes and circulation types in the Czech Republic, 1961-2020

This paper presents the characteristics of extreme temperatures in the Czech Republic, as calculated from homogenized series of daily maximum (TMAX) and daily minimum (TMIN) temperatures recorded by 133 climatological stations throughout the territory in the 1961-2020 period. In general, statistically significant increasing linear trends were recognized in series of absolute TMAX, absolute TMIN, numbers of summer days, tropical days, days with tropical nights, heat-wave, and warm-anomaly days. Significant decreasing linear trends appeared in series of numbers of frost days, ice days, cold-wave, and cold-anomaly days. Objective classification of circulation types demonstrated the importance of anticyclonic types (especially those with warm airflow from the southern quadrant) and an unclassified type in the development of summer hot extremes, while winter cold extremes were linked to cold (north-)easterly advection. Significant changes in the frequency of certain circulation types emerged, as well as an increasing number of anticyclonic types conducive to hot extremes, a trend that contributed to their more frequent occurrence in recent decades. Existing trends in temperatures were complemented by spatiotemporal analysis of extreme temperatures, the characteristics of extremes and the circulation types in the two normal periods of 1961-1990 and 1991-2020. These exhibited significant differences in means and variances. The results obtained are also discussed in a broader context.

Automated summary

This paper presents the characteristics of extreme temperatures in the Czech Republic, based on data from 133 climatological stations recorded between 1961 and 2020. The study found significant increasing trends in absolute maximum and minimum temperatures, as well as in the number of summer days, tropical days, days with tropical nights, heat-waves, and warm-anomaly days. Decreasing trends were observed in the number of frost days, ice days, cold-waves, and cold-anomaly days. The analysis also showed the importance of anticyclonic circulation types and their impact on summer hot extremes, as well as the link between winter cold extremes and cold (north-)easterly advection. Changes in the frequency of circulation types were detected, with an increasing number of anticyclonic types contributing to the more frequent occurrence of hot extremes in recent decades. Spatiotemporal analysis revealed significant differences in means and variances between the periods of 1961-1990 and 1991-2020.