CONICET | Buscador de Institutos y Recursos Humanos

Extreme hydrological events such as protracteddroughts can have profound impacts on society. The rate of occurrence andseverity of droughts is expected to increase with anthropogenic climate changeon most continents. Quantifying the contribution of the anthropogenic forcingto current and future drought requires having an envelope of naturalvariability of past drought from long instrumental record and drought proxies. The coverageof the instrumental climate record of South America is very sparse prior to 1950,but tree-ring chronologies developed from forests along the Andes Cordillera providean excellent source of past moisture variability. The number and quality ofclimate sensitive tree-ring records in the region south of 12°S havesignificantly increased during the past few decades. As a result, there is nowa robust network of tree-ring records suitable for assessing the range ofhydroclimate variability during the past several centuries. Herein, we combine 290annually-resolved tree-ring chronologies with an improved version of instrumentalself-calibrated Palmer Drought Severity Index data (scPDSI) to derive the SouthAmerican Drought Atlas (SADA) - a spatially gridded (0.5° x 0.5°) reconstructionsof austral summer (DJF) drought for the region from 12ºS to 56ºS. The SADAreconstructions extend from 1400 to 2015 CE and were developed using the EnsemblePoint-by-Point Regression (EPPR) method. The SADA provides annual maps ofsummer drought/wetness and a new geographical perspective of the occurrence,severity, and duration of previously known and unknown dry and wet extremeevents in the SADA domain. Leading principal components 2 and 3 of the SADAdomain are related to the sea surface temperatures from the tropical PacificNiño 3.4 sector (r=0.43) and the southern annular mode (r=0.31), respectively.This confirms the known large-scale forcings of regional climate (such as ENSOand SAM) on drought variability in South America. The SADA represents a more completespatiotemporal reconstruction of hydroclimate variability over the SouthAmerica compared to previous estimates based on instrumental and naturalrecords. Our study provides additional insights into SADA domain hydroclimaticvariability through the identification of the long-term wet or dry events andthe temporal evolution of extremes in summer drought during the past sixcenturies. The 600-year drought reconstructions also provide the temporal contextfor recent drought variability that is critically needed for climate modelingand predictions. SADA was created using the same reconstruction methods toproduce the drought atlases in North America (NADA, MXDA), Europe (OWDA), SEAsia (MADA), and Australia-New Zealand (ANZDA). These common properties providea global perspective of drought variability for the direct comparisons of thedrought atlases.