Influência do oceano atlântico tropical na vazão da Bacia Hidrográfica do Rio São Francisco

Abstract

The São Francisco River Basin (638,466 km²) has its spring in the headwater in the Minas Gerais State, in Serra da Canastra, and its river mouth in the Atlantic Ocean is positioned between the States of Alagoas and Sergipe. Although the streamflow regime of this basin is known, the influences of the oceans on its streamflow regime are unknown, including the Tropical Atlantic Ocean. Thus, the objective of this study was to investigate possible influences of the Tropical Atlantic Ocean on the São Francisco River Basin streamflow. For this purpose, the monthly averages from 1982 to 2015 of the data of: naturalized flow, Sea Surface Temperature (SST) of the tropical Atlantic Ocean, Long Wave Radiation (ROL), and Precipitation were used. For these data the linear tendency was removed and the anomalies of the variables were calculated by subtracting the value of the monthly average of the monthly climatological average (1982-2015). The investigation on possible relations between the ocean and the streamflow was made from simple and delayed correlation in one and two months. The correlations obtained between flow anomalies and SST anomalies, as well as the correlation between flow anomalies and ROL anomalies, were moderate, lower than -0.4. The region of occurrence of this correlation was predominantly the Brazilian southern coast, including lagged correlations of 1 and 2 months, where the correlation was strong, lower -0.6, and the correlation area in the tropical South Atlantic Ocean basin was increased considerably. This correlation pattern indicates a significant presence of transient systems and the South Atlantic Convergence Zone (SACZ) contributing to rainfall in the Upper São Francisco River and streamflow in the basin. The correlation of the anomaly of these variables was moderate to strong, from 0.4 to 0.6. In general, it is possible that the transient meteorological systems and the SACZ are the most relevant synoptic systems in the control of the rainfall regime and consequently the flow in the São Francisco River Basin. Further analyzes are still needed to better understand the influence of the oceans and the synoptic processes that predominantly operate at the headwater and that influence their rainfall and flow regime.