Unprecedented late 20th century drought condition in the Southern Altiplano: A multi-century lake area tree-ring based reconstruction

MARIANO S. MORALES; DUNCAN A. CHRISTIE; JULIETA CARILLA; HECTOR RICARDO GRAU; RICARDO VILLALABA

Trieste

Workshop; CLIVAR-ICTP Workshop on Decadal Climate Variability and predictability: Challenge and Opportunity.; 2015

International Centre for Theoretical Physics (ICTP)

<!-- /* Style Definitions */p.MsoNormal, li.MsoNormal, div.MsoNormal{mso-style-unhide:no;mso-style-qformat:yes;mso-style-parent:"";margin:0cm;margin-bottom:.0001pt;mso-pagination:widow-orphan;font-size:12.0pt;font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman";mso-ansi-language:ES;}.MsoChpDefault{mso-style-type:export-only;mso-default-props:yes;font-size:10.0pt;mso-ansi-font-size:10.0pt;mso-bidi-font-size:10.0pt;}@page WordSection1{size:612.0pt 792.0pt;margin:70.85pt 3.0cm 70.85pt 3.0cm;mso-header-margin:36.0pt;mso-footer-margin:36.0pt;mso-paper-source:0;}div.WordSection1{page:WordSection1;}-->Size fluctuations in endorheic lakes innorthwestern Argentina (NWA) and southwestern Bolivia (SWB) are very sensitiveto basin hydrological balances, and consequently, very vulnerable todeleterious effects from climatic changes. The management of these waterresources and their biodiversity requires a comprehensive knowledge of theirnatural variability over multiple time scales. In this study, we present amulti-century reconstruction of past lake-area fluctuations in NWA and SWB. Theevidence used to develop and validate this reconstruction includes satelliteimages and a century-long tree-ring record from P. tarapacana. Inter-annual fluctuations in lake area of nine lakeswere quantified based on Landsat satellite images over the interval 1975 to2009. A regional P. tarapacanatree-ring chronology, composite from two sampling sites, was used as predictorsin a regression model to reconstruct the mean annual (January-December) lakearea from the nine lakes. The reconstruction model captures 62% of the totalvariance in lake-area fluctuations and shows adequate levels ofcross-validation. This high-resolution reconstruction covers the past 601 yrand characterized the occurrence of annual to multi-decadal lake areafluctuations and its main oscillation modes of variability.  Our reconstruction points out that the latetwenty century decrease in lake area was exceptional over the period 1407?2007;a persistent negative trend in lake area is clear in the reconstruction andconsistent with glacier retreat and other climate proxies from the Altiplanoand the tropical Andes. Since the mid 1970s, the Vilama-Coruto lake systemrecorded an accelerated decrease in area consistent with an increasing recurrenceof extremely small lake-area events. Throughout the 601 yr, the reconstructionprovides valuable information about spatial and temporal stabilities of therelationships between changes in lake area, ENSO, and PDO, highlighting thePacific influence over most modes of lake area variability. Global and regionalclimate models for the Altiplano project a marked reduction in precipitation tothe end of the 21st century, exacerbating presently dry conditions. Theseresults provide a baseline for the historical range of variability in lakefluctuations and thus should be considered for the management of biodiversityand water resources in the Central Andes during the next decades.