Comparison of Extreme Rainfall Phenomena in Central Europe: A Case Study of the 1997 and 2024 Flood Events Using a Novel Precipitation Event Intensity Index (PEII)

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Abstract In light of the recent extreme flood event in central Europe, which had devastating consequences for many countries, the evolution of these events and how their intensity can be better characterized has gained attention. This study provides a comparative case study of two major flood-producing rainfall episodes in central Europe, focusing on differences in storm structure and spatial footprint as represented in ERA5-Land. The events selected are the flood in July 1997 and the recent flood in September 2024, as both had similar magnitude, origins, and spatial coverage. To answer the posed questions, ERA5-Land hourly total precipitation was used to calculate the number of continuous hours exceeding a 50 mm h −1 rain-rate threshold and the number of such events in each grid cell. Based on that, to assess and compare the intensity and scale of those events, the new index is proposed: precipitation event intensity index (PEII). The results highlight event-specific differences across the affected countries and show how PEII can distinguish between more continuous versus more episodic high-intensity rainfall structures. PEII is shown to be a useful diagnostic tool for comparing the internal structure (persistence versus fragmentation) of high-intensity rainfall events across large regions and is further explored in relation to river runoff where discharge data are available.

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