El Niño e seus impactos na América do sul: clima atual e cenários futuros

Abstract

The spatial evolution of two different El Niños types and its impacts on South America (SA) were evaluated using observed sea surface temperature (SST) data from Extended Reconstructed Sea Surface Temperature (ERSST) and SST derived from historical and future simulations of Coupled Model Intercomparison Project Phase 5 (CMIP5). The two El Niño types analyzed in this study show distinct patterns, one located in the central tropical Pacific, called CP, and other in the east-tropical Pacific, called EP. For historical simulations, the HadGEM2-ES, CNRM-CM5 and MPI models were used and for the future simulation, only CNRM-CM5. The results confirm that the events selection method is consistent with many others available in the literature. Regarding the simulations, the CNRM-CM5 model provided better representation of the SST anomaly pattern of the EP and CP events. Regarding the impact on the SA precipitation, the show that during El Niño EP the observed anomaly pattern is similar to the expected for canonical El Niño, with above normal precipitation in southeastern and southern of SA and reduced precipitation in large part of northern and northeastern of SA during DJF. The impact of CP events on the South America precipitation are different from the El Niño EP. Overall, for the EP El Niño mature phase (DJF), the CNRM and HadGEM models captured the dipole pattern for SA precipitation, with positive (negative) rainfall anomalies in the southern and southeast (north and northwest ) parts of SA. However, both caused decrease in rainfall over Northeast Brazil. The MPI model represented the rain reduction on the northern portion, but was not sensitive to increased (decreased) precipitation in the southern/southeastern (northwest) region of SA. Regarding the CP El Nino for same period, the three models represented the increase rainfall in Southern SA and reduction in northern and northwestern SA. However, HadGEM and MPI models reduced rainfall on Brazilian Northeast in contrast to the observed. For future simulation the results with the CNRM model, in general it can be said that the behavior of SST anomaly pattern in relation to historical, presents slight difference in frequency and intensity of events for both El Niño types, wherein the weakened EP SST anomaly pattern type, especially in the mature phase (DJF (+1)) and the CP type particularly early in the evolution of phenomenon was a slight enhancement, but the lifetime of such events (CP) is smaller in the future in relation to historical, which carries a decay of the ATSM DJF and MAM period.