Two Millennia of Floods in a Key Area of the Mediterranean Basin Documented by Archaeological and Historical Sources: Climatic Implications and Future Perspectives

There is growing concern that ongoing climate change is altering the frequency and magnitude of river floods. However, the lack of long-term observational time series of flood events makes verification difficult, particularly in the Mediterranean region, where complex orography produces strong sub-regional variability. Because available instrumental discharge records are too short to identify low- and high-frequency periodicities and to disentangle climatic and anthropogenic forcings, it is necessary to integrate measured data with non-systematic hydrological information derived from historical documents, archaeological evidence, and sedimentary proxies. Here we present the reconstruction and analysis of floods of the Arno and Serchio rivers, located in a key area of the Mediterranean Basin, based on archaeological and historical sources. Both rivers are well known for their destructive floods affecting the cities of Lucca, Pisa, and Florence. The earliest historically documented flood dates to 217 BCE. Phases of increased flood occurrence are identified during the early Roman period (1st–2nd centuries BCE) for the Serchio River, while enhanced flood activity affecting both rivers is observed during the Late Antique Little Ice Age. In addition, a new flood record for the Arno River since the 12th century CE was developed using an automated methodology for the analysis of written sources. The reconstructed series allows the identification of several flood-rich phases in the Arno basin, some of which broadly coincide with periods of reduced solar activity previously recognized in other Italian rivers. In contrast, correlations with reconstructed North Atlantic Oscillation indices appear variable and dependent on the selected index and time lag. Overall, these results emphasize the importance of long-term archaeological and historical records for providing a broader context to recent flood variability and for improving the interpretation of flood patterns in Mediterranean river systems.