Discovering Megadroughts Across the Northern Hemisphere from Long Tree-Ring Records: Climate Histories and Human Impacts During the Common Era

The discovery of megadroughts in continental-scale drought atlases derived from long tree-ring records covering much of the Common Era has brought attention to the possible societal impacts that unusual hydroclimatic events have had on human history. These “events” include both megadroughts and unusual wet periods that are unprecedented when compared to the modern hydroclimatic record. Examples of such events coupled with societal impacts from drought atlases developed for North America, Europe, and Asia will be shown. Together, they indicate the likelihood that past megadroughts and pluvials over those regions played a significant role in influencing the history of human activities in the affected regions and elsewhere.

Edward R. Cook is the Ewing Lamont Research Professor at Lamont-Doherty Earth Observatory of Columbia University. His educational background comes from the University of Arizona Laboratory of Tree-Ring Research. With Gordon Jacoby, Ed co-founded the Tree-Ring Laboratory at Lamont in 1975 and is currently its Director. His research accomplishments have emphasized the development of new statistical methods for processing tree-ring data, the development of networks of tree-ring chronologies for climate reconstruction, and the reconstruction of climate from tree rings around the world. These long-term research activities have resulted in the development of drought atlases – gridded continental-scale reconstructions of drought from tree rings - covering most of the North Hemisphere:  the North America Drought Atlas (NADA), the Monsoon Asia Drought Atlas (MADA), and the Old World Drought Atlas (OWDA). They span most or all of the Common Era and are being used extensively by climatologists, ecologists, foresters, and historians because the information content in these atlases spans a vast array of disciplines and research interests. Drought atlas development is now being extended to the Southern Hemisphere in the form of the Australia-New Zealand Drought Atlas (ANZDA) and the South American Drought Atlas (SADA).