Old World Megadroughts and Pluvials During the Common Era

Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in 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-to3 year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin for 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 prior to the 20th century with inadequate understanding as to why. The OWDA provides new data for performing detailed data/model comparisons for attributing the causes of Old World drought and wetness due to both forced and internal variability.