INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Precipitation changes in the South American Altiplano (18°-23° S) during the Late Intermediate Period (1000-1450 D.C.) and their impacts on human populations
MARIANO S. MORALES; AXEL E. NIELSEN; RICARDO VILLALBA; DUNCAN A. CHRISTIE
Conferencia; 4th Southern Desert Conference; 2014
Dry farming and pastoral economies in the Bolivian Altiplano are extremely sensitive to fluctuations in climate, particularly water availabilty. However, it is difficult to examine these relationships over time due to the scarcity, shortness and heterogeneity of the available instrumental climate records. The recent development of well-replicated, climate-sensitive tree-ring records from Polylepis tarapacana allows the reconstruction of past environmental conditions at various temporal scales and the examination of the links between climate and human events in the area. P. tarapacana trees growing in the Altiplano between ca 4500-5200m, has remarkable dendrochronological potential and moreover Pre-Columbian populations regularly used Polylepis wood for construction. We used a network of P. tarapacana chronologies to reconstruct precipitation variability in the Bolivian Altiplano for the past 700 years. This reconstruction has periods of several decades or even a century with precipitation below the mean and exhibits a negative trend since 1930s to present. Archeologists have identified a major shift in settlement patterns in the Altiplano during the 13th and 14th centuries. Low-elevation, vulnerable villages occupied until the 13th century were rapidly abandoned in favor of highly visible, frequently fortified sites with difficult access, a phenomenon related to the onset of a state of endemic warfare. It has been proposed by Nielsen (2001) that conflicts were triggered by periods of droughts resulting in repeated crop failure and high animal mortality forcing Altiplano dry farmers to fight for the control of irrigable land on both sides of the Andes. Our precipitation reconstruction gives preliminary support to this idea. Almost the entire 14th century was characterized by below average precipitation with a single sub-decadal humid period between 1300 and 1307. This severe century long drought period persisted until the mid15th century. We propose that the negative impact of this persistent centennial drought on local agricultural-based societies triggered a period of war in the Altiplano during the 13th and 14th centuries. The tree ring reconstruction also suggests that the last 30 yr were the driest since 1300, consistent with observed and climate-model projections for warmer-drier conditions over the Altiplano.