Old World megadroughts and pluvials during the Common Era

TLDR

Climate models project future Mediterranean drying and Fennoscandian wetting driven by greenhouse gas forcing. The study develops the Old World Drought Atlas to contextualize future climate projections with historical hydroclimatic variability. The OWDA compiles year‑to‑year tree‑ring maps of summer wetness and dryness across Europe and the Mediterranean to attribute past droughts and wetness to forced or internal climate variability. The OWDA corroborates historical drought records and shows that 11th‑ and mid‑15th‑century European megadroughts were severe, extensive, and prolonged, underscoring gaps in understanding their causes.

Abstract

Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other “Old World” climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the “Old World Drought Atlas” (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. The OWDA matches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability.