Tropical Andes tree-ring records and the hydroclimate fluctuations over the northern Altiplano and the Yungas from central Andes of Peru

MARIANO S. MORALES

Potsdam

Workshop; 2K Network Phase 4; 2023

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The summer monsoon is the dominant mode of climatic variability over the tropical and subtropical region of South America and is responsible for more than 70% of the total annual rainfall in its core region. The new tree ring chronology network developed allows:1- To identify the climatic sensitivity of tree growth in Cedrela, Juglans, Polylepis and Escallonia species.The growth of most of these species were sensitive to precipitation variations, but others such as Polylepis rodolfo-vasquezii from the humid Puna show positive growth response to temperatures.2- To reconstruct the precipitation for the Altiplano and Andes of central Peru during the last 400 and 200 years, respectively.3- To identify the main climate variability drivers that influence rainfall at interannual and multidecadal scales in the Altiplano and Andean-Amazonian region during the last 400 and 200 years.Our study provides an overview of the temporal evolution of the late-spring–mid-summer precipitation for the period 1625–2013 CE at the northern South American Altiplano, allowing for the identification of wet or dry periods based on a regional reconstruction from three Polylepis tarapacana chronologies. An increase in the occurrence of extreme dry events, together with a decreasing trend in the reconstructed precipitation, has been recorded since the 1970s in the northern Altiplano within the context of the last 4 centuries.We report here an annually resolved precipitation reconstruction for the montane forest of the peruvian Andes based on growth rings of Cedrela odorata, C. nebulosa, and Juglans neotropica tree species. The precipitation reconstruction shows decadal to multidecadal variations with several below and above average rainfall intervals. An increase in droughts events is evident from 1980 to present.The spatial correlation analysis between the reconstructed and observed NDJ precipitation of the northern South American Altiplano and the gridded GPCP NDJ precipitation for the common period 1979–2013 shows consistent spatial patterns. High correlation coefficients are observed across the SA Altiplano and projected towards the south-central Andes, and in the equatorial sector of Brazil. Weaker positive correlations are observed within the region of convection over the Amazon basin. The spatial correlation pattern showed a significant negative relationship between the reconstructed precipitation and the SSTs from the tropical east-central Pacific Ocean for the period 1949–2013. The strongest correlations are found in the region south of the NIÑO 3 sector (~2–13  S, 100–150 W). The spatial correlation analysis between the reconstructed and observed precipitation of the Yungas and the gridded annual (Nov-Oct) GPCP precipitation for the common period 1979–2007, shows high correlation coefficients across the tropical Andes and towards the equatorial lowlands of Brazil. The spatial correlation field between SST and our Amazon-Andes reconstruction for the 1950–2010 period shows significant and negative correlation values between the precipitation reconstruction and SSTs in the tropical Pacific Ocean (a clear ENSO‐like pattern). Also, the significant and negative correlations with the tropical north Atlantic Ocean temperatures suggest that other sources of variability such as the intertropical Atlantic SSTs may have influence in the rainfall of the study region.The main moisture source over the Yungas montane forests is monsoon core region east of the Andes, as revealed by the OLR correlations over the Amazon Basin.