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.

Bavarian State Department for Cultural Heritage Thierhaupten 86672 Germany

Biotechnical Faculty University of Ljubljana Ljubljana SI 1000 Slovenia

Climatic Research Unit University of East Anglia Norwich NR4 7TJ UK

Competence Center for Underwater Archaeology and Dendrochronology Office for Urbanism City of Zürich Zürich 8008 Switzerland

Cornell Tree Ring Laboratory Cornell University Ithaca NY 14853 USA

DeLaWi Tree Ring Analyses Windeck D 51570 Germany

Dendrology Department University of Forestry Sophia 1756 Bulgaria

Department of Earth Sciences Gothenburg University Gothenburg SE 405 Sweden

Department of Ecology University of Barcelona Barcelona 08028 Spain

Department of Forest Ecology Czech University of Life Sciences Prague 16521 Czech Republic

Department of Geography Johannes Gutenberg University Mainz 55099 Germany

Department of Physical Geography Stockholm University Stockholm SE 106 Sweden

Dipartimento di Scienze della Terra e dell'Ambiente Università degli Studi di Pavia Pavia 27100 Italy

Ecoclimatology Technische Universität München Freising 85354 Germany

Environmental Research and Education Mistelbach 95511 Germany

Faculty of Forestry Istanbul University Bahcekoy Sariyer 34473 Istanbul Turkey

Faculty of Forestry University of Applied Sciences Weihenstephan Triesdorf Freising 85354 Germany

Flanders Heritage Agency Brussels 1210 Belgium

Forest Research and Management Institute Calea Bucovinei Campulung Moldovenesc 725100 Romania

German Archaeological Institute Berlin 14195 Germany

Institut für Geographie Universität Innsbruck Innsbruck A 6020 Austria

Institute for Forest Growth University of Freiburg Freiburg 79106 Germany

Jahrringlabor Hofmann Nürtingen 72622 Germany

Labor Dendron Basel 4057 Switzerland

Laboratory of Tree Ring Research University of Arizona Tucson AZ 85721 USA

Laboratory of Tree Ring Research University of Arizona Tucson AZ 85721 USA ; Nicolaus Copernicus University Torun 87 100 Poland

Lamont Doherty Earth Observatory of Columbia University Palisades NY 10964 USA

Moravian Dendro Labor Brno 61600 Czech Republic

National Museum of Denmark Copenhagen DK 1220 Denmark

Natural Resources Institute Finland Rovaniemi FI 96301 Finland

Navarino Environmental Observatory Messinia 24001 Greece

NTNU University Museum Norwegian University of Science and Technology Trondheim 7012 Norway

Oxford Dendrochronology Laboratory Oxford University Oxford RG4 7TX UK

Paleoecology Center Queens University Belfast BT7 1NN Northern Ireland

Royal Netherlands Meteorological Institute De Bilt 3730 Netherlands

School of Geography and Geosciences University of St Andrews St Andrews KY16 9AL Scotland

Slovenian Forestry Institute Ljubljana SI 1000 Slovenia

Swiss Federal Research Institute WSL Birmensdorf 8903 Switzerland

Technische Universität Dresden Tharandt D 01737 Germany

TeSAF Department Università degli Studi di Padova Agripolis Legnaro 1 35020 Italy

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