A multi-century tree-ring inference on lake size fluctuations from the Southern Altiplano

MARIANO S. MORALES; JULIETA CARILLA; H. RICARDO GRAU; LEONARDO PAOLINI

Medellin

Simposio; LOTRED-SA 3rd International Symposium; 2014

High-elevation endorheic lakes represent a major source of biodiversity, and regulate hydrological regimes in the Southern Altiplano. The ecosystem of these Ramsar wetlands in North West Argentine (NWA) and South West Bolivia (SWB) are sensitive to the basins hidrological balance. In recent years attention has been focused on the possibility of deleterious effects from climatic change. The management of these water resources requires comprehensive knowledge of their natural variability over multiple time scales. In this study we present a multi-century reconstruction of past lakes size fluctuations in the NWA and SWB, inferred on Polylepis tarapacana tree rings records. Between 1975 and 2009 interannual lake size fluctuations from six lakes were calculated with Landsat images. Also, a network of four P. tarapacana tree-ring chronologies were developed, time series features of growth variation were summarized. Correlations analyses were performed to screen potential predictor tree-ring chronologies for reconstruction models. The interannual lake size fluctuations were positively correlated with interannual variations of the radial growth of P. tarapacana records. The tree-ring chronologies were applied in a regression model to reconstruct a time series of the mean January-December lake size average of six endorheic lakes. The tree-ring reconstruction covers the past 309 years, and captures 36% of the lake size variance. Though statistically weak (R2 = 0.36), the reconstruction verifies adequately in cross-validation. The 20th century was unusual in a long-term context; a persistent negative trend in lake size has been recorded in the reconstruction, according with glacier retreat and a severe decrease in a reconstructed precipitation performed for the Altiplano region for the past 700 years. To link lake size fluctuations with major climate forcing, such as the Niño3.4, PDO and the South American Monsoon, spectral analyses will be performed and discussed. Further research is needed to better discriminate the tree-ring signal for lake size variation from the signal due to localized precipitation.