Combining instrumental, historical, and coastal marine sedimentary archives to analyse floods variability in northwestern Italy during the last thousand years

Understanding Earth’s changing climate is a crucial challenge. However, the available time series of direct measurements are often insufficient to fully capture climatic processes that unfold over centuries and millennia. Combining history and geology can fill this gap. Focusing on rainfall and flood events, this study proposes a multidisciplinary approach to integrate the sedimentary and meteorological records of the Magra River (Northern Italy), using historical data as a bridge between the two datasets. A pristine record of near shore river- mouth deposits, covering the last thousand years, is analysed, interpreting sand layers as flood events. The results are merged with a coherent historical record of floods and river activity spanning six centuries and instrumental measurements spanning two centuries. The timing of the deposition of the sand layers interpreted as flood events is reasonably consistent with rainfall data and historical records, testifying to the reliability of the river mouth sedimentary record as a proxy for river discharge. The complete dataset and the comparison with other basins of the northwestern Mediterranean clearly indicate common floods during the 1150–1200, 1350–1400, 1550–1590, 1720–1820, and 1950–1970 intervals, all periods characterised by predominantly negative phases of the North Atlantic Oscillation.