Historical environmental change has increased disastrous flooding in Italy's northwestern Apennines (1511–2021 CE)

Damaging hydrological events can profoundly impact societies. This study reconstructs the longest flood history to date for the Orba River Basin (ORB) in northwestern Italy, from 1511 to 2021 CE. Using the Annual Flood Damage Index, we establish a continuous annual hydrological time-series. Our analysis, incorporating a seasonally-weighted function for interannual storm effects, uncovers anthropogenic influences on the ORB's fluvial landscape and flood characteristics. Specifically, a change-point emerged around the end of the Little Ice Age and the subsequent warming period (c. 1816), after which more intense storms prevailed. Remarkably, recent flood peaks align with heightened climate hazards, proving more extreme and unpredictable on a small scale in disaster-prone areas. Additionally, this study acknowledges competitive forcing factors on a larger scale, including landscape changes due to peasant civilisation expansion and 19th-century deforestation. Broader-scale factors, exemplified by the global impact of the 1815 eruption of Tambora in Indonesia, may have influenced the post-1816 climate conditions. These results emphasise the importance of considering both human-induced disturbances and precipitation occurrences in comprehending a territory's environmental history.