Abstract An extraordinary rainfall affected Central Europe during the passage of Storm Boris in September 2024. This study focuses on the Hrubý Jeseník Mts. (NE Czechia), where one-day and cumulative totals were highest, to evaluate hillslope–channel responses in the most severely impacted headwaters and to place this extreme in a long-term regional context. A field inventory identified 30 new debris-flow paths—about 28% of historically known paths. Despite unprecedented multi-day (up to 703 mm in 72 h) and 24 h totals (up to 386 mm), debris-flow sizes were comparable to past events, indicating strong topographic predisposition. About 80% of both new and old paths fall within the top two deciles of a combined topographic wetness index–Melton Ruggedness Number metric (calculated in SAGA GIS and ArcGIS Pro). Using hourly gauge data and an intensity–duration (ID) curve, the 2024 event was unprecedented for rainfall durations > 10 h, with increasing hourly intensity likely explaining the relatively high debris-flow occurrence compared with earlier large-scale precipitation events. Long-term inheritance of extremes was examined with Wavelet Transform Analysis of regional May–October daily maxima (1900–2024). The early twentieth century showed short-term (5–10-year) cyclicity in extreme (95th percentile) and very extreme (99th percentile) rainfall, while recent decades exhibit more random, nonstationary patterns. Cross-wavelet Coherence suggests episodic linkages with ENSO and Scandinavian Blocking. This study warns of rising debris-flow risk in medium-altitude mountain areas—where hazards are underestimated—calls for stronger mitigation, and stresses the value of long-term extreme-weather analysis to better assess consequences of increasing hydroclimate variability.
Tichavský et al. (Sun,) studied this question.
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