6-kyr record of flood frequency and intensity in the western Mediterranean Alps – Interplay of solar and temperature forcing
Résumé
The high-resolution sedimentological and geochemical analysis of a sediment sequence from Lake Savine(Western Mediterranean Alps, France) led to the identification of 220 event layers for the last 6000 years.200 were triggered by flood events and 20 by underwater mass movements possibly related to earthquakesthat occurred in 5 clusters of increase seismicity. Because human activity could influence theflood chronicle, the presence of pastures was reconstructed through ancient DNA, which suggested thatthe flood chronicle was mainly driven by hydroclimate variability. Weather reanalysis of historical floodsallow to identify that mesoscale precipitation events called “East Return” events were the main triggersof floods recorded in Lake Savine. The first part of this palaeoflood record (6e4 kyr BP) was characterizedby increases in flood frequency and intensity in phase with Northern Alpine palaeoflood records. Bycontrast, the second part of the record (i.e., since 4 kyr BP) was phased with Southern Alpine palaeofloodrecords. These results suggest a palaeohydrological transition at approximately 4 kyr BP, as has beenpreviously described for the Mediterranean region. This may have resulted in a change of flood-pronehydro-meteorological processes, i.e., in the balance between occurrence and intensity of local convectiveclimatic phenomena and their influence on Mediterranean mesoscale precipitation events in thispart of the Alps. At a centennial timescale, increases in flood frequency and intensity corresponded toperiods of solar minima, affecting climate through atmospheric changes in the Euro-Atlantic sector