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North American Megadroughts in the Common Era: Reconstructions and SimulationsDuring the Medieval Climate Anomaly (MCA), Western North America experienced episodes of intense aridity that persisted for multiple decades or longer. These megadroughts are well documented in many proxy records, but the causal mechanisms are poorly understood. General circulation models (GCMs) simulate megadroughts, but do not reproduce the temporal clustering of events during the MCA, suggesting they are not caused by the time history of volcanic or solar forcing. Instead, GCMs generate megadroughts through (1) internal atmospheric variability, (2) sea-surface temperatures, and (3) land surface and dust aerosol feedbacks. While no hypothesis has been definitively rejected, and no GCM has accurately reproduced all features (e.g., timing, duration, and extent) of any specific megadrought, their persistence suggests a role for processes that impart memory to the climate system (land surface and ocean dynamics). Over the 21st century, GCMs project an increase in the risk of megadrought occurrence through greenhouse gas forced reductions in precipitation and increases in evaporative demand. This drying is robust across models and multiple drought indicators, but major uncertainties still need to be resolved. These include the potential moderation of vegetation evaporative losses at higher atmospheric [CO2], variations in land surface model complexity, and decadal to multidecadal modes of natural climate variability that could delay or advance onset of aridification over the the next several decades. Because future droughts will arise from both natural variability and greenhouse gas forced trends in hydroclimate, improving our understanding of the natural drivers of persistent multidecadal megadroughts should be a major research priority.
Document ID
20160004955
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Cook, Benjamin I.
(NASA Goddard Inst. for Space Studies New York, NY United States)
Cook, Edward R.
(Lamont-Doherty Earth Observatory Palisades, NY, United States)
Smerdon, Jason E.
(Lamont-Doherty Earth Observatory Palisades, NY, United States)
Seager, Richard
(Lamont-Doherty Earth Observatory Palisades, NY, United States)
Williams, A. Park
(Lamont-Doherty Earth Observatory Palisades, NY, United States)
Coats, Sloan
(Colorado Univ. Boulder, CO, United States)
Stahle, David W.
(Arkansas Univ. System Fayetteville, AR, United States)
Villanueva Diaz, Jose
(Centro Nacional de Investigacion Disciplinaria en Relación Agua-Suelo Planta-Atmosfera Lerdo, Mexico)
Date Acquired
April 8, 2016
Publication Date
March 29, 2016
Publication Information
Publication: WIREs Climate Change
Publisher: Wiley
Volume: 7
Issue: 3
e-ISSN: 1757-7799
Subject Category
Meteorology And Climatology
Report/Patent Number
GSFC-E-DAA-TN31129
Distribution Limits
Public
Copyright
Other
Keywords
atmospheric temperature
volcanoes
variability
North America
climate
Earth surface
drought
greenhouse effect
anomalies

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