CONICET | Buscador de Institutos y Recursos Humanos

A marked reduction in rainfall and a highfrequency of severe droughts have been documented in the subtropical Andes of SouthAmerica during the past decades. In this region, changes in precipitation arestrongly influenced by sea surface temperatura over the Pacific Ocean andphenomena such as El Niño-Southern Oscillation (ENSO) and the Pacific DecadalOscillation (PDO). However, long-term trends in precipitation appear to be associatedwith changes in global circulation patterns in response to global warming. Apoleward expansion of the HadleyCirculation (HC) is projected in responseto anthropogenic climate changes, shifting precipitation patterns andincreasing the subtropical dry zone affected by frequent droughts. The particularnorth-south extent of the Andes and the existence of precipitation sensitivedendrochronological records from the outer tropics to Patagonia, offers aunique opportunity to document expansions contractions in the HC in theSouthern Hemisphere during the last centuries to millennia. In this presentation,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, Austrocedruschilensis and Araucaria araucana) are used to comparatively assess theinfluence of the HC expansion on reducing rainfalls over the subtropical Andeanzone of South America. Although the interannual-decadal variability in rainfallresponds to climatic oscillatory modes such as ENSO-PDO, similarities inlong-term oscillations (centuries or longer) in these regions show theinfluence of the expansion-contraction of the HC on precipitation atcontinental scale. In particular, the marked negative trends in precipitationduring the last 4-5 decades from the outer tropical to the subtropical Andesmay provide evidence of an unprecedented expansion of HC in the Southern Hemisphere associated with concurrent globalwarming.