Short-Term Climate Predictability of Summer Rainfall on the Paraná Basin Based on Atlantic and Pacific Sea Surface Temperatures

CAMILLONI, INÉS

Foz de Iguazú

Conferencia; 8th International Conference on Southern Hemisphere Meteorology and Oceanography; 2006

American Meteorological Society

A better understanding of the variability and potential climate predictability of rainfall is vital or those regions where the hydroelectric power is essential to satisfy the energy demands. From this point of view, the Paraná basin is important for Argentina, Brazil, Paraguay economies due to the large number of dams operating on this river and its tributaries that supply important amounts of the energy required in these countries. The annual rainfall cycle in the Paraná basin show abundant summer rainfall that leads to the management of water in the dams in a way that favours the accumulation during summertime and increases its release during winter, reducing the annual discharge amplitude of the river. Therefore, climate variations and particularly the interannual summer rainfall variability in this region carry important economic and social impacts. The objectives of this study are (i) to analyze the extent to which the dominant patterns of interannual variability of the summer rainfall over the Paraná basin are linked to the Atlantic and Pacific sea surface temperatures (SSTs) of previous months and (ii) to address what features of the space-time evolution of these SSTs could lead to a successful forecast of the austral summer rainfall on the Paraná basin. A principal component analysis was performed on summer rainfall anomalies of the austral summer for the period 1970-99. The first and second leading modes account for the 22.8% and 19.4% of the total variance respectively. The first mode has negative loadings over the SACZ region and positive ones over northern Argentina, Uruguay and southern Brazil. This pattern is associated to reduced/increased precipitation due to the northward/southward displacement of the SACZ. The second leading mode has positive loadings over the Upper Paraná basin and negative ones in the SACZ region and east-central Argentina and Uruguay. Time series of these two principal components show positive trends associated to enhanced summer rainfall over most of Southeastern South America. Three key regions were identified from this analysis: the SACZ region and the Upper Paraná and Middle-Lower Paraná basins. Linear correlation coefficients were calculated between mean summer rainfall anomalies over these regions and simultaneous and up to six months previous SST anomalies in the Atlantic and Pacific oceans. The SACZ and Middle-Lower Paraná basins rainfall anomalies are highly correlated with SSTs anomalies in the Pacific Ocean that reflects the ENSO pattern and with positive SSTs anomalies in the South Atlantic region during the period August-November. The Upper Paraná basin summer rainfall anomalies are positively correlated with SST anomalies in the South Pacific during October-November. Results indicate that only during ENSO events there is some predictability of summer rainfall in the Middle-Lower Paraná basins based on Atlantic and Pacific SSTs up to six months before summer.