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

CHRISTIE, D.; MUNDO I A; MARCOTTI, E.; URRUTIA, R.; VILLALBA R.; LEQUESNE, C.; LARA, A.; SRUR, A. M.; MORALES M.; VIALE, M.; AMOROSO, M.M.; RODRIGUEZ CATON, M.

Mendoza

Conferencia; Ameridendro 2016 Third American Dendrochronology Conference; 2016

Amarked reduction in rainfall and a high frequency of severe droughtshave been documented in the subtropical Andes of South America duringthe past decades. In this region, changes in precipitation arestrongly influenced by sea surface temperature over the Pacific Oceanand phenomena such as El Niño-Southern Oscillation (ENSO) and thePacific Decadal Oscillation (PDO). However, long-term trends inprecipitation appear to be associated with changes in globalcirculation patterns in response to global warming. A polewardexpansion of the Hadley Circulation (HC) is projected in response toanthropogenic climate changes, shifting precipitation patterns andincreasing the subtropical dry zone affected by frequent droughts.The particular north-south extent of the Andes and the existence ofprecipitation sensitive dendrochronological records from the outertropics to Patagonia, offers a unique opportunity to documentexpansions-contractions in the HC in the Southern Hemisphere duringthe last centuries to millennia. In this presentation, precipitationreconstructions, based on massively replicated dendrochronologicalrecords, from the Altiplano (16°-20°S;Polylepistarapacana);the central Andes of Chile (32°-36°S, Austrocedruschilensis)and northern Patagonia (39°-43°S, Austrocedruschilensis andAraucariaaraucana)are used to comparatively assess the influence of the HC expansion onreducing rainfalls over the subtropical Andean zone of South America.Although the interannual-decadal variability in rainfall responds toclimatic oscillatory modes such as ENSO-PDO, similarities inlong-term oscillations (centuries or longer) in these regions showthe influence of the expansion-contraction of the HC on precipitationat continental scale. In particular, the marked negative trends inprecipitation during the last 4-5 decades from the outer tropical tothe subtropical Andes may provide evidence of an unprecedentedexpansion of HC in the Southern Hemisphere associated with concurrentglobal warming.