Impact of the equatorial Pacific and South Atlantic SST anomalies on extremes in austral summer precipitation over Grande river basin in Southeast Brazil

Abstract

ABSTRACTGrande river basin (GRB) is located in Southeast Brazil, and is socio‐economic important for water supply and electricity generation from its hydroelectric plant reservoirs affected by the inter‐annual variability of precipitation. Dry and rainy summers are selected using rainfall data from the National Water Agency (Agência Nacional de Águas–ANA) in Brazil to assess the influence of the equatorial Pacific and South Atlantic sea surface temperature (SST) anomalies, and to depict the intensity and positioning of large‐scale circulation patterns that might affect the precipitation extremes in summer over GRB. The European Centre for Medium‐Range Weather Forecasts global reanalysis provides the meteorological variables to construct the composites of the years of extremes (dry and rainy) in summer precipitation, as well as the preceding springs. The results show that extreme dry summers in GRB are characterized by neutral to negative SST anomalies in the equatorial Pacific and positive anomalies in the subtropical South Atlantic near Brazilian coastline. Rainy extremes are associated with El Niño conditions in Niño 1 + 2, Niño 3 and 3.4 regions during summer and preceding spring. Extreme rainy summers display negative anomalies of SST in the subtropical South Atlantic, coinciding with the northerly South Atlantic Convergence Zone positioning. In GRB, anomalous rainy springs are mostly followed by anomalous dry summers. Large‐scale atmospheric circulation anomalies in the preceding springs to summer precipitation extremes in GRB show characteristic features that might be proven useful in seasonal predictions of hydro‐meteorological extremes.