Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century

MORALES, MARIANO S.; COOK, EDWARD R.; BARICHIVICH, JONATHAN; CHRISTIE, DUNCAN A.; VILLALBA, RICARDO; LEQUESNE, CARLOS; SRUR, ANA M.; FERRERO, M. EUGENIA; GONZÁLEZ-REYES, ÁLVARO; COUVREUX, FLEUR; MATSKOVSKY, VLADIMIR; ARAVENA, JUAN C.; LARA, ANTONIO; MUNDO, IGNACIO A.; ROJAS, FACUNDO; PRIETO, MARÍA R.; SMERDON, JASON E.; BIANCHI, LUCAS O.; MASIOKAS, MARIANO H.; URRUTIA-JALABERT, ROCIO; RODRIGUEZ-CATÓN, MILAGROS; MUÑOZ, ARIEL A.; ROJAS-BADILLA, MOISES; ALVAREZ, CLAUDIO; LOPEZ, LIDIO; LUCKMAN, BRIAN H.; LISTER, DAVID; HARRIS, IAN; JONES, PHILIP D.; WILLIAMS, A. PARK; VELAZQUEZ, GONZALO; ALISTE, DIEGO; AGUILERA-BETTI, ISABELLA; MARCOTTI, EUGENIA; FLORES, FELIPE; MUÑOZ, TOMÁS; CUQ, EMILIO; BONINSEGNA, JOSÉ A.

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

NATL ACAD SCIENCES

Año: 2020 vol. 117 p. 16816 - 16823

0027-8424

South American (SA) societies are highly vulnerable to droughtsand pluvials, but lack of long-term climate observations severelylimits our understanding of the global processes driving climaticvariability in the region. The number and quality of SA climatesensitivetree ring chronologies have significantly increased in recentdecades, now providing a robust network of 286 records forcharacterizing hydroclimate variability since 1400 CE. We combinethis network with a self-calibrated Palmer Drought Severity Index(scPDSI) dataset to derive the South American Drought Atlas(SADA) over the continent south of 12°S. The gridded annual reconstructionof austral summer scPDSI is the most spatially completeestimate of SA hydroclimate to date, and well matches pasthistorical dry/wet events. Relating the SADA to the Australia?NewZealand Drought Atlas, sea surface temperatures and atmosphericpressure fields, we determine that the El Niño?Southern Oscillation(ENSO) and the Southern Annular Mode (SAM) are stronglyassociated with spatially extended droughts and pluvials over theSADA domain during the past several centuries. SADA also exhibitsmore extended severe droughts and extreme pluvials sincethe mid-20th century. Extensive droughts are consistent with theobserved 20th-century trend toward positive SAM anomalies concomitantwith the weakening of midlatitude Westerlies, whilelow-level moisture transport intensified by global warming hasfavored extreme rainfall across the subtropics. The SADA thusprovides a long-term context for observed hydroclimatic changesand for 21st-century Intergovernmental Panel on Climate Change(IPCC) projections that suggest SA will experience more frequent/severe droughts and rainfall events as a consequence of increasinggreenhouse gas emissions.