This page provides a new perspective on flash flood hazards in Germany.

We used DWD’s RADKLIM product to identify the ten most extreme precipitation events in Germany from 2001 to 2022. We then assumed that any of these top 10 events could have happened anywhere in Germany. In other words, these events were shifted around all over Germany. For all resulting positions of the precipitation fields, we simulated the corresponding peak discharge for any affected catchment with an area smaller than 750 km². From all the realisations of this simulation experiment, the maximum peak discharge was identified for each catchment.

These results might help to reduce the element of surprise in disaster risk management, by allowing a view on what could happen in case certain extreme events occurred elsewhere. Such scenario analysis is referred to as “counterfactual thinking”, and a “downward counterfactual search” strives to identify constellations with impacts worse than observed for the actual event itself.

Please find a comprehensive presentation of this approach in our recent preprint: Voit, P., and Heistermann, M.: A downward counterfactual analysis of flash floods in Germany, Nat. Haz. Earth Syst. Sc. Disc. [preprint], in review.

In the map below, you can compare the counterfactual maximum peak to the original maximum peak that resulted from the actual rainfall events over a catchment from 2001 to 2022. We show the unit peak discharge which normalizes the peak flow by the upstream basin area. The results are presented per federal state. When hovering over the map, you can also see which rainfall event caused the maximum counterfactual peak.

Please use the drop-down menu to select a different state and then hit the Update map button to update the map. Please be patient, loading data may take a while…

This is the list of extreme preciptation events that were analysed: