CONICET | Buscador de Institutos y Recursos Humanos

The climate changes observed in the last decades has raised concern among policy and decision makers about the importance of the knowledge and prediction of climate. In particular southeastern South America(SESA) has experimented large positive precipitation trends during the 20th century that impacted many socio-economic sectors. However, regional studies show that decadal variability has a large influence in SESAprecipitation. As a consequence, a deeper knowledge of decadal climate variability in the region is needed in order to project near term future changes with a lower degree of uncertainty. The Fifthphase or the World Climate Research Program-Coupled Model Intercomparison Project (WCRP/CMIP5) Experiment provides an excellent opportunity to investigate physical processes involved in SESAprecipitation changes and their predictability. The mean precipitation evolution since the last 150 years exhibit in SESA considerable multi-decadal variation that have been identified inprevious works as forced by the tropical ocean variability. Therefore, in order to better understand the influence of the observed large-scale interannual variability of the sea surface temperatures on austral summer rainfall in SESA in a global warming context, a singular value decomposition analysis was performed. The first mode shows over the 1902-2010 period, a clear global warming signal, mainly related to warming in Pacific and Indian Ocean inassociation with a rainfall increase in SESA. The temporal series of the mode exhibits variability going from interannual to interdecadal trends. Decadal variability is remarkable, with a particular phaseshift at around the middle 1970s. After detrending the series, the first mode resembles an El Niño-Southern Oscillation like pattern,which also has a remarkable variability on decadal scales. Moreover,it was found that the relationship between sea surface temperaturevariations, especially in the Tropical Pacific Ocean, and SESAprecipitation is non stationary, exhibiting decadal variations,related with changes in the teleconnections between both regions. Historical and Decadal simulations of WCRP/CMIP5 coupled general circulatio nmodels (CGCM) are considered in order to make a preliminary evaluation of the representation of the austral summer rainfall variability and trends in Southeastern South America and its connection with ocean variability. Models are able to represent a significant positive trend over SESA in agreement with observations, which could be related to frequency changes in the rainfall leading pattern. Representation of the main pattern of climate variability was assesed. Preliminary results using short-term climate predictions show that the simulations are able to reproduce the leading mode of variability, as well as the teleconnection pattern linking the tropical Pacific-Indian Ocean sector with southern South America.