From 30 May to 6 June 2024, prolonged rainfall over southern Germany resulted in severe flooding. The occurrence of such events represents a core research area for ClimXtreme, a research network funded by the Federal Ministry for Education and Research (BMBF). A principal objective of ClimXtreme is to establish and extend a knowledge base that informs decision-making, thereby contributing to the implementation of adequate measures to prevent severe damage caused by extreme weather events.

Concurrently, the objective of the research is to gain a deeper comprehension of the physical processes that transform an extreme weather event into a significant hazard. One particularly pertinent question that requires further investigation and is of particular interest to the public is the extent to which recent extreme events are influenced by human-induced climate change and how they will behave in a future climate.

This report employs methodologies developed within the ClimXtreme research network to examine the present flood event. The results presented here therefore reflect the current state of ongoing research. A comparison of the various scientific approaches reveals that the categorisation of the event in relation to previous extremes is contingent on the chosen perspective, resulting in an inconsistent representation at first glance. 

Summary

In summary, precipitation levels exceeded 250 mm over a six-day period, occurring within a stationary large-scale weather situation over Europe. The heavy rainfall event comprised precipitation patterns at varying spatial and temporal scales, detailed in Fig. 6 in Section 1.3.2. Furthermore, the precipitation exhibited pronounced convective components. Notably, the event spanned an extensive spatial extent over a considerable duration. In terms of precipitation intensity, however, only return periods of a centennial event were exceeded locally. It is noteworthy that comparable or more intense events in terms of extent, precipitation duration and quantity have been observed on multiple occasions in the past.

However, the 2024 flood represents the second-largest discharge record anomaly in the region over the past century, following the 2013 event. Accordingly, the simulated runoff response is also exceptional, with some cases implying return periods of well over 100 years.

A review of station data from southern Germany revealed no discernible trend in the statistics of extreme precipitation events that could be attributed to climate change. The probabilistic attribution study assigns a 30-year return period to the current event, whereby the probability of this event has increased by a factor of 1.4 (uncertainty: 0.8 to 4.4) compared to a pre-industrial climate. Furthermore, it is anticipated that the probability will continue to increase in a warmer climate. Concerning the specific event, regional simulations indicate that it would have manifested at a lesser intensity in a pre-industrial climate. The elevated overall intensity of the event in the present climate is predominantly attributable to an increase in precipitation of moderate intensity at the smaller scale. However, high-resolution climate simulations indicate no statistically significant changes in the spatio-temporal characteristics of heavy rainfall events between the past, present, and future.

To access the complete report, please click on the following link. Please note that this resource is only available in German.