Paleoflood hydrology: reconstructing rare events and extreme flood discharges

Understanding the occurrence of large magnitude flood events is essential in a changing climate. Yet, these flood events are rare, and its estimation is challenging due to the shortage of the gauging station records and their limited spatial distribution. The geological and botanical evidence left by past extreme flood events can overcome this drawback, extending the instrumental records by hundreds or thousands of years. Geological flood records are often obtained from stratigraphic sequences of sand and silt deposited in slackwater (SWDs) or in eddy sedimentary environments and dated by geochronological methods (radiocarbon and luminescence techniques). Botanical flood records are described as external disturbance on trees (e.g., scar or tilted stems) or changes in vegetation patterns caused by flood impacts and dated using tree-rings procedures. Both geological and botanical evidence define paleostage indicators (PIs) that can be used to estimate the flood discharges using hydraulic modeling. These flood magnitude estimations are essential inputs for improving flood-frequency analysis. Here we revise the latest advance in this hydrological discipline and underline its scientific and technological interest to design critical infrastructures (e.g., dams and bridges), risk planning, and climate change impact studies.