| Summary: | Global climate change is projected to significantly modify recent climate conditions. Especially the increased occurrence of large-scale intense precipitation causing severe flooding, would highly affect the Alpine region and its foreland, since floods represent a major natural hazard in the Alps. In order to assess natural flood variability and its forcing factors that could improve accurate projections of these climate extremes, we established a 10'000 year-long flood reconstruction of the Central Alps based on 10 Northern and 5 Southern Alpine lacustrine sedimentary archives. Lakes with a certain relief in the respective catchment record individual flood events by distinct sediment layers (flood turbidites). These layers contain high amounts of terrigenous material that was mobilized during intense precipitation events and transported to the next downstream lake. Therefore, individual lake sediment successions uncover the local flood history. To reconstruct a regional flood pattern and thus rather a synoptic Alpine intense rainfall signal, we studied multiple Alpine lake records. The accuracy of the lacustrine flood chronology is verified by a good correlation with historical flood reconstructions from the Northern Alpine region covering the last 500 years. Regarding Northern Alpine flood variability over the past 2500 years, a coincidence between high flood frequencies and low summer temperatures is apparent, which we interpret in terms of changing North Atlantic atmospheric circulations accompanied by varying summer mean temperatures. In particular, we propose a weaker (stronger) expression of the subtropical high-pressure zone accompanied by lower (higher) summer mean temperatures, which favors (impede) the occurrence of Atlantic storm tracks affecting the Central Alpine region and thus enhance (decrease) the occurrence of intense precipitation. Over the past 10'000 years, the overall pattern of the Northern and Southern Alpine flood frequency anti-correlate with variations in total solar irradiance that ...
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