A multi-proxy stalagmite record indicates a shift in forcing of 20th Century drought events in Normandy

Abstract

Drought events are increasingly impacting Europe. The study of past droughts helps disentangle the different factors that trigger hydrological drought, helping to forecast future drought severity. Here we identify the historical drought events of the 20th and 21st centuries in geochemical records of a stalagmite from Caumont cave in Northern France and develop a mechanistic understanding of their root causes. Subannually-resolved stable isotope records (δ13C and δ18O) and trace element data are directly compared with historical climatic records. δ13C, δ18O, Mg, and Sr peaks align well with most of the historical drought events of the 20th and 21st centuries. The comparison reveals a good correspondence between summer effective rainfall and δ13C, Mg, and Sr concentrations. Further comparison of geochemical records with the precipitation-evapotranspiration index (SPEI) reveals a change in the drought forcings for the past two decades. During most of the 20th century, droughts appear driven by a pluvial regime, whereas since the late 1990s, drought was driven by higher evapotranspiration due to increased temperature.