South American tree-ring records support the recent expansion of the Hadley Cell circulation over the Southern Hemisphere

VILLALBA, RICARDO; CHRISTIE, DUNCAN; MORALES, MARIANO; LEQUESNE, CARLOS; MUNDO, IGNACIO; VIALE, MAXIMILIANO; LARA, ANTONIO; MARCOTTI, EUGENIA; AMOROSO, MARIANO; SRUR, ANA; URRUTIA, ROCIO; RODRÍGUEZ CATÓN, MILAGROS

Conferencia; Third American Dendrochronology Conference ? AmeriDendro2016; 2016

A marked reduction in rainfall and a high frequency of severe droughts have been documented in the subtropical Andes of South America during the past decades. In this region, changes in precipitation are strongly influenced by sea surface temperature over the Pacific Ocean and phenomena such as El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). However, long-term trends in precipitation appear to be associated with changes in global circulation patterns in response to global warming. A poleward expansion of the Hadley Circulation (HC) is projected in response to anthropogenic climate changes, shifting precipitation patterns and increasing the subtropical dry zone affected by frequent droughts. The particular north-south extent of the Andes and the existence of precipitation sensitive dendrochronological records from the outer tropics to Patagonia, offers a unique opportunity to document expansions-contractions in the HC in the Southern Hemisphere during the last centuries to millennia. In this presentation, precipitation reconstructions, based on massively replicated dendrochronological records, from the Altiplano (16°- 20°S; Polylepis tarapacana); the central Andes of Chile (32°-36°S, Austrocedrus chilensis) and northern Patagonia (39°-43°S, Austrocedrus chilensis and Araucaria araucana) are used to comparatively assess the influence of the HC expansion on reducing rainfalls over the subtropical Andean zone of South America. Although the interannual-decadal variability in rainfall responds to climatic oscillatory modes such as ENSO-PDO, similarities in long-term oscillations (centuries or longer) in these regions show the influence of the expansion-contraction of the HC on precipitation at continental scale. In particular, the marked negative trends in precipitation during the last 4-5 decades from the outer tropical to the subtropical Andes may provide evidence of an unprecedented expansion of HC in the Southern Hemisphere associated with concurrent global warming.