Relationships between Precipitation Anomalies in Uruguay and Southern Brazil and Sea Surface Temperature in the Pacific and Atlantic Oceans

Abstract

This study focuses on precipitation in Uruguay and the Brazilian state of Rio Grande do Sul, which extend along the Atlantic coast of southern South America. The present paper has two principal goals: 1) to describe the annual cycle of precipitation and 2) to investigate the relationships between its anomalies and those in sea surface temperature (SST) in the Pacific and Atlantic oceans. The dataset is provided by 40 rainfall stations almost evenly distributed in space and covers the period 1917–80. The tools used in support of this research include principal component and canonical correlation analyses. It is found that total precipitation tends to be evenly distributed during the year. The largest spatial variability in the monthly deviations from the annual mean appears as a west–east (inland–coastal) dipole with the largest positive values in the west during early fall and midspring, and in the east along the Atlantic coast during winter. The second mode of rainfall variability appears as a north–south dipole with the largest positive values in the south during late summer and late fall, and in the north during early spring and early summer. The third mode appears primarily as a north–south dipole along the western boundary with the largest positive values in the southwest during fall and in the northwest during early spring. These modes explain 60%, 19%, and 8% of the total variance. Five subregions are identified according to similarities between the characteristics of the annual cycles in their rainfall stations. It is shown that there are significant relationships between anomalies in rainfall and in SST in the Pacific and Atlantic oceans. Some of these relationships confirm the results of previous studies, such as the links between the El Niño–Southern Oscillation phenomenon in the equatorial Pacific Ocean and rainfall anomalies in Uruguay during late spring–early summer and late fall–early winter. Other relationships have not been reported before, such as the links between SST anomalies in the southwestern Atlantic Ocean and rainfall anomalies in the entire region during October–December and April–July. It is also found that when SST anomalies are considered in both oceans simultaneously, their links with rainfall anomalies are in some cases enhanced and in others weakened.