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

VILLALBA, RICARDO ; CHRISTIE, D; MORALES, M; LEQUESNE, C; MUNDO, I; VIALE, M; LARA, A; MARCOTTI, E.; AMOROSO, M; SRUR, A; URRUTIA-JALABERT, R.; MILAGROS RODRIGUEZ CATÓN

Mendoza

Conferencia; AMERIDENDRO 2016; 2016

IANIGLA - CONICET

A marked reduction in rainfall and a high frequency of severedroughts have been documented in the subtropical Andes ofSouth America during the past decades. In this region, changes inprecipitation are strongly influenced by sea surface temperatureover the Pacific Ocean and phenomena such as El Niño-SouthernOscillation (ENSO) and the Pacific Decadal Oscillation (PDO).However, long-term trends in precipitation appear to beassociated with changes in global circulation patterns in responseto global warming. A poleward expansion of the HadleyCirculation (HC) is projected in response to anthropogenicclimate changes, shifting precipitation patterns and increasingthe subtropical dry zone affected by frequent droughts. Theparticular north-south extent of the Andes and the existence ofprecipitation sensitive dendrochronological records from theouter tropics to Patagonia, offers a unique opportunity todocument expansions-contractions in the HC in the SouthernHemisphere during the last centuries to millennia. In thispresentation, precipitation reconstructions, based on massivelyreplicated 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 tocomparatively assess the influence of the HC expansion onreducing rainfalls over the subtropical Andean zone of SouthAmerica. Although the interannual-decadal variability in rainfallresponds to climatic oscillatory modes such as ENSO-PDO,similarities in long-term oscillations (centuries or longer) in theseregions show the influence of the expansion-contraction of theHC on precipitation at continental scale. In particular, the markednegative trends in precipitation during the last 4-5 decades fromthe outer tropical to the subtropical Andes may provide evidenceof an unprecedented expansion of HC in the SouthernHemisphere associated with concurrent global warming.