Central-European extreme precipitation event in September 2024 in comparison with similar events

In the second decade of September 2024, Central Europe was hit by heavy rainfall lasting several days, which caused extensive flooding. The most affected area was the northeast of the Czech Republic, where similar events are known from the relatively recent past (July 1997) as well as from the history (e.g. July 1903). These events will be compared with each other with regard to the amount and course of the rainfall and also from the point of view of causal atmospheric conditions.

In terms of daily precipitation totals, the event from September 2024 clearly dominates because as much as 385.6 mm of precipitation was measured during only one day (14 September) at the Loučná nad Desnou, Švýcárna station. This value is a new maximum not only for the Czech Republic, but also for the wider area of ​​Central Europe. Comparison with older events is, however, complicated due to the short length of the data series from this station. We therefore focus primarily on stations that measured during all the mentioned events.In addition to daily totals, we will also analyze subdaily precipitation intensity and multi-day precipitation totals.

In addition to the extremity of point precipitation totals, we will also evaluate the areal extremity, using the weather extremity index. The value of this index simultaneously expresses the duration of the rainfall, the size of the affected area and the average rainfall return period within this area. Also from this perspective, the September 2024 event exceeded older events, as in addition to higher rainfall totals, it also affected a larger area.

Extreme precipitation is caused by extreme atmospheric conditions. The event will therefore be explained by anomalies in meteorological variables that characterize the conditions favorable to heavy precipitation. Such variables include moisture fluxes, vertical velocity, relative vorticity, and others.