Multidecadal “megadroughts” were a notable feature of the climate of the American Southwest over the Common Era, yet we still lack a comprehensive theory for what caused these megadroughts and why they curiously only occurred before about 1600 CE. Nathan Steiger, a research scientist in the PaleoDynamics Lab, has published a paper using the Paleo Hydrodynamics Data Assimilation (PHYDA) product, in conjunction with radiative forcing estimates, to determine the causes of megadroughts in the American Southwest. He and coauthors report strong evidence that these droughts were driven by unusually frequent and cold central tropical Pacific sea surface temperature (SST) excursions in conjunction with anomalously warm Atlantic SSTs and a locally positive radiative forcing. This assessment of past megadroughts provides the first comprehensive theory for the causes of megadroughts and their clustering, particularly during the Medieval era. The work also provides the first paleoclimatic support for the prediction that the risk of American Southwest megadroughts will markedly increase with global warming (see here and here).
The PHYDA was developed by Nathan as a postdoctoral scientist in the PaleoDynamics Lab and is available here. His megadrought paper can be found here.
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