INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Comparison between the variability of Río Atuel and Río Chubut hydrological regimes in interannual to intraseasonal scales and their relationships with local and global atmospheric conditions
ARANEO D.; RIVERA J.; VILLALBA R.
Conferencia; 11th meeting of the International Conference on Southern Hemisphere Meteorology and Oceanography; 2015
American Meteorological Society
By principal component (PC) analysis applied to Río Atuel and Río Chubut hydrological annual cycles, the main modes of inter-annual to intra-seasonal variability of the surface runoffs for each river were studied. Relationships between PCs and the local variability of precipitation and temperature, and the associated global atmospheric circulation were also analyzed. The first four PCs explain for about 49, 21, 10 and 8% of the total variance for Atuel; and 33, 23, 15 and 10% for Chubut. For Río Atuel, PCs 1 and 2 discriminates between precipitation- and temperature-related components associated with variations in snow accumulation and advances/delays of the streamflow annual peak, respectively. Above-average streamflows related to abundant snowfalls in the basin are associated with northward shifts in stormtracks that are remotely induced by above-average sea surface temperatures in the equatorial Pacific. Otherwise, earlier streamflow peaks in November-December are concurrent with above-average temperatures across the Atuel basin induced by enhanced meridional circulation from the tropics due to the strengthening of the South Atlantic anticyclone, linked to the persistent positive phase of the Southern Annular Mode. Additionally, years with reduced streamflows in January (and proportionally larger streamflow in November-December), are associated with anomalous air cooling at high levels induced by low pressures over the region as part of a quasi-zonal stationary Rossby wave train extending from Australia to the South American-South Atlantic sector. Additionally, PC3 represents the alternation of streamflow anomalies between October-November, December, January and February; while PC4 represents the alternation of anomalous runoffs between November, January and February. Both PC 3 and 4 patterns are linked to the intra-seasonal variation of temperature anomalies over the basin region, which variability acts promoting or inhibiting the melting of winter snow and consequent abnormal increase or decrease in river flows, respectively. In turn, these temperature anomalies are associated with pressure anomalies in height and/or low levels, largely related to Rossby wave trains extending along the South Pacific and South America. For Río Chubut, PC1 represents a fluctuation of runoffs above/below normal mainly during June-November, related to the variability of moisture contribution from tropical regions of central Pacific, due to pressure anomalies in subtropical latitudes of the ocean, mainly during May-August. The CP2 is characterized by abnormal streamflows during June-July that change signs in August-November. These anomalies are mainly related to the pressure at highlevels. For water deficit and surplus in June-July and August-November, respectively, a negative pressure anomaly is observed at high levels above the center of Argentina, causing precipitation in the litoral but inhibiting them in Patagonia. This anomaly is located off the southern coast of Chile in subsequent months, inducing instability and increasing the precipitation in the basin. PC3 and PC4 represent intra-seasonal streamflow fluctuations mainly related to monthly to bimonthly local variability of rainfall and, in a lesser degree, temperatures. These local anomalies would be explained by abnormal pressure/circulation at high levels from synoptic to global scales; in several cases, as part of quasi-stationary systems or wave trains, extending over the region and adjacent oceans.