A tree-ring based reconstruction of the Southern Bolivian Altiplano precipitation since A.D. 1300

MORALES, M; CHRISTIE, D; VILLALBA R; ARGOLLO J; LARA A; PACAJES J; SOLIZ C

FOZ DO IGUAZU

Congreso; THE MEETING OF THE AMERICAS; 2010

Instrumental records of climate in the tropics are short, fragmentary and heterogeneous. Longer records are needed to understand the nature of climate variations, and how the interannual modes of tropical climate variability (such as ENSO) have evolved under changes in long-term background conditions. Polylepis tarapacana (Rosaceae) is a small- to medium-size tree growing on the slopes of the Andean tropical volcanoes in Bolivia and adjacent areas of Peru, Chile and Argentina (17–23°S) between 3900 and 5200 m elevation. Previous dendrochronological studies indicate that the radial growth of P. tarapacana is influenced by precipitation during the summer preceding the ring formation. Based on extensive collections of Polylepis samples across its range of distribution, more than 15 ring width chronologies have recently been developed. Some of these records extend for more than 700 years. Ring-width variations from Polylepis were used as predictors of regional records of summer precipitation across the Southern Altiplano (Fig.1). The model used for the reconstruction captures c.a. 54% of the total annual precipitation variance. The reconstruction covers the past 700 years and captures interannual to decadal scales of variability in annual precipitation. Several persistent droughts were observed throughout the last 700 years, as well as a negative trend in precipitation during the last 150 years. This record represents the first dendrochronological precipitation reconstruction for the outer tropics in South America and demonstrates the highly significant skill of P. tarapacana as a precipitation proxy.