INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Variability of the Atuel River streamflow annual cycle and its relationship with the tropospheric circulation
ARANEO D. C.; AGOSTA E.
Congreso; Meeting of the Americas; 2013
The headwaters of the Atuel River are located in the eastern (Argentinean) side of the high subtropical Andes in southern South America. The present work aims to study the low frequency (interannual) variability of the annual cycle of the river streamflows by applying Principal Component Analysis to the annual hydrograph in order to extract the main features of the annual regime. The analysis yields that the first Principal Component (PC1) and the second Principal Component (PC2) explain each 48% and 22%, respectively, of the total variance. The direct (indirect) mode of PC1 represents an annual cycle characterized by streamflows above (below) the mean. The PC2 represents the seasonal lag of the streamflow peak that can occur by the late spring (direct mode) or by the early autumn (indirect mode). The visual inspection of the PCs factor loadings timeseries reveals that the PC1 pattern is predominantly indirect during the periods 1917-1976 and 1988-1999, which suggests the propensity to undergo extended periods (spells) of streamflow deficit. In turn, the PC2 pattern is predominantly indirect from 1906 to 1926 and direct from 1948 to 2002, suggesting a somewhat propensity to undergo streamflow peaks during the late spring in most of the second half of the last century. Correlation fields between PCs factor loadings timeseries and some meteorological variables are likewise estimated in order to examine potential links between the interannual variability of the annual streamflow cycle and the tropospheric circulation. The PC1 streamflow pattern can be significantly associated with winter and spring tropospheric circulation conditions. The direct (indirect) PC1 pattern is related with significant positive (negative) pressure anomalies localized over the southeastern Pacific. Warmer (cooler) sea surface temperature (SST) anomalies are similarly observed in the central equatorial Pacific. Hence, the years with streamflows above (below) the mean would possibly relate with sufficient (insufficient) snowfalls in the high subtropical Andes as a result of northward (southward) shift of the stormtracks that can be associated with the tropospheric circulation anomalies in the southeastern Pacific induced by the SST anomalies in the equatorial Pacific (El Niño/La Niña events). The PC2 streamflow pattern is significantly associated with late spring and early summer tropospheric circulation conditions. The years with a propensity to undergo streamflow peaks in the late spring (the early autumn) could be associated with anomalous air warming (cooling) over the subtropical Andes mainly due to the strengthening (weakening) of the South Atlantic anticyclone and the induced meridional circulation over subtropical latitudes.