The South American Drivers of Megadroughts and Pluvials over the Past 600 years.

MARIANO S. MORALES; EDWARD R. COOK; JONATHAN BARICHIVICH; DUNCAN A. CHRISTIE; RICARDO VILLALBA

San Francisco

Conferencia; AGU fall meeting; 2019

Given the heavy dependence on natural resources, extreme protracted droughts and pluvials have profound impacts on South American society. However, the absence of a complete spatial coverage of long-term climate observations prevents modeling and predicting the dynamic processes that drive its complex spatiotemporal climatic variability. Herein, we combine 290 annually-resolved tree-ring chronologies with instrumental self-calibrated Palmer Drought Severity Index data (scPDSI) to derive a South American Drought Atlas (SADA). The SADA include 2715 reconstructions, and provides spatially gridded (0.5° x 0.5°) annual maps of summer (DJF) moisture over the continent south of 12ºS between 1400 to 2000 CE. The SADA also provides a new geographical perspective of the occurrence, severity, and duration of previously known and unknown dry and wet extreme events in the study domain. Our results indicate that severe droughts have become more spatially widespread since the mid 20th century. Also, past droughts and pluvials were closely related to the combined impacts of large-scale ENSO-SAM circulation patterns on SADA domain. The SADA provides the spatio-temporal context for recent drought/pluvial variability, information critically needed for climate modeling and predictions. SADA was developed using the same Ensemble Point-by-Point Regression (EPPR) method used to produce the drought atlases in North America (NADA, MXDA), Europe (OWDA), SE Asia (MADA), and Australia-New Zealand (ANZDA). A global hydroclimate variability perspective will be possible through the direct comparisons of the drought atlases.