Changes in convective precipitation characteristics during the warm season in the Czech Republic

Convective precipitation is a key component of the hydrological cycle and a major driver of extreme rainfall, flash floods, and other high-impact weather events. Under climate warming, changes in the thermodynamic environment are expected to affect the intensity, spatial structure, duration, and frequency of convective storms. This study investigates long-term changes in convective precipitation over the Czech Republic using time series from 19 observation stations covering the period 1982–2021.

Precipitation totals were classified into convective and stratiform components using an algorithm based on SYNOP reports. The analysis focuses on the warm half of the year (April–September), when convective precipitation dominates. We examine six precipitation characteristics: total precipitation, number of rainy days, rain intensity index, 98th percentile of daily precipitation (P98), seasonal maximum, and the convective fraction. Trends are estimated using Sen’s slope, and their statistical significance is assessed with the Mann–Kendall test. Positive trends are found for all characteristics except the rain intensity index.

In addition, we analyse days with heavy convective precipitation and their relationship to atmospheric circulation. Heavy convective precipitation is defined as a convective precipitation amount exceeding the mean P98 threshold over the study period. Atmospheric circulation types are classified using the Jenkinson and Collins (1977) method. This approach identifies circulation types based on three indices: flow direction, strength, and vorticity. Our results show that heavy convective precipitation most frequently occurs under cyclonic, northwesterly, northerly, and westerly circulation types.