Multicentenary streamflow variations in the Subtropical Andes of Argentina (22‒30°S) inferred from instrumental records and tree rings.

FERRERO, M.E.; VILLALBA, R.; DE MEMBIELA, M.; FERRI HIDALGO, L.

Los Reyunos, San Rafael, Mendoza

Workshop; CRN-CRA 2047; 2014

IAI, IANIGLA

Runofffrom the subtropical Andes is the main source of freshwater andrivers in northwestern Argentina and continues to be used forconsumption and irrigation of agricultural fields. These activitiesare seriously affected by climate variability: analyses ofinstrumental precipitation and streamflow records for the past 60years indicate a period of enhanced inter-annual and inter-decadalvariations during the last decades. In this contribution we present along-term perspective of streamflow for the Bermejo River, a majorriver in the subtropical region of Argentina. This streamflowreconstruction covers the period 1680-2001 and was performed usingprincipal component regression models based on sensitive tree-ringwidth series. Composite tree-ring chronologies from Juglansaustralis, Cedrela lilloi andSchinopsis lorentziiwere used to reconstruct the May-October streamflow variations.Monthly rainfall and instrumental streamflow data were used to assessthe spatial relationship and temporal validation between climaticdata and tree-ring records. The regression model explains 52% of thevariance of May-October Bermejo discharge (R2adj= 0.499) for the period 1941-1992. Analysis of the frequency,intensity and duration of pluvials and droughts, indicates asustained increase in streamflow since the 1960s, which isexceptional since 1680. To examine the large-scale climate influencesin our study area, Pearson´s correlation coefficients were calculatedbetween the reconstructed and instrumental Bermejo records with0.5x0.5° gridded (NCEP-NCAR)interpolated precipitation (1975-2001) and outgoing longwaveradiation data (OLR, commonly used as proxy of precipitation intropics; 1980-2005 period) respectively, indicating that the SouthAmerican monsoon system is the main climatic source of regionalprecipitation and the discharge of rivers in northern Argentina.The development of long-term reconstructions provide new informationon significant hydroclimatic variables for the subtropical Andes anddischarge to adjacent downstream areas. They also contribute tounderstanding past and present climate variations for the region andthe related large-scale atmospheric features that drive thesevariations.