Fluvial deposits of the Ahr River reveal recurring high-magnitude flood events during the last 1500 years

Floods are one of the most critical environmental threats in Central Europe. They are responsible for more than half of the economic damage caused by environmental hazards in Germany. The magnitude of the 2021 Ahr flash flood has far exceeded the values of previous flood hazard forecasts. This was due to significantly underestimated hazard assessments, as the former hydrological models considered exclusively instrumental discharge records. Due to the recording interval being too short, previous high-magnitude flood events were not considered in flood hazard assessments. Historical flood events from written sources were also not included in the official flood hazard assessment. In this study, we show the importance of geomorphological records from Ahr flood deposits for reconstructing past high-magnitude flood events. Our analysis shows that centennial to millennial-scale high-energy flood deposits are not the exception but the rule. In addition to the catastrophic flash flood of 2021, the historically documented flash floods of 1910 and 1804 were geomorphologically proven as well as a previously unknown flash flood event from the approx. 6^th century AD. The results document the high potential of floodplain archives for reconstructing high-magnitude flood events in Central European rivers, allowing a systematic reassessment in terms of occurrence and frequency of high-magnitude flood events.