Southern hemisphere lowfrequency troposheric circulation components and their contribution to river runoffs changes in Central Eastern Patagonia

MAENZA R.; ARANEO D.; AGOSTA E.

Roma

Conferencia; 5th International Conference on Reanalysis (ICR5); 2017

ECMWF

Patagonia is under influence of the westerlies that drive the amount and distribution of precipitation in the Southern Hemisphere (SH) middle latitudes. Two sub regions with highly distinct precipitation features are: wet Western Patagonia, from the Pacific coast to the Andean highs; and dry Eastern Patagonia, leeward the Andes in the Argentine steppe plateau towards the Atlantic. The cold season (Apr-Sep) is the rainy season over the mountains in central Patagonia (40°S-50°S), leading to snow accumulation over river catchment areas. The winter snow feeds river runoffs to the east in EP. The Tecka-Gualjaina (TG) River is one of those which drain their streamflow into the South Atlantic, from the Andes to the Atlantic. We explored the influence of tropospheric circulation and sea surface temperature (SST) anomalies on the interannual-to-decadal streamflow variations of the TG River for the season of maximum streamflow (Jun-Nov) and the season of minimum streamflow (Dec- May). The maxima show negative trend along records. There is a change in the streamflow anomalies by the early 1980s, evolving from a positive predominance before to a negative one after. The minima show stationarity (no trend). The intra-decadal quasi-cycles are dominant in both seasonal streamflow maxima and minima. Teleconnections related to the streamflow were analyzed using ERA-Interim, NCEP/NCAR I, 20C, and ERA-20C reanalysis datasets and other oceanic and atmospheric global datasets. Detrended streamflow maxima are linked to a quasi-stationary Rossby wave (QSW). Tropospheric circulation anomalies, symmetric about the equator, are possibly associated with tropical convection, induced by anomalous SST in the equatorial western Pacific. The QSW affects the position and intensity of the subtropical and polar jets, altering winter precipitating transient perturbations. Detrended streamflow minima are linked to a high latitude annular mode-like variability, modulated by a mid-latitude wave-3 structures over the Pacific and Atlantic. Trend analysis and inhomogeneity tests on SH tropospheric circulation fields and SST anomalies, show significant slow components consistent with the trend and changes in the TG streamflow. Trends in tropospheric fields during the river peak season are present even if inhomogeneities are removed.