O Papel do ENOS na Variabilidade Climática da Bacia Amazônica durante o Último Milênio em Simulações Paleoclimáticas

Abstract

The present work aimed to investigate the influences of ENSO on the climatic variability of the Amazon Basin in the Last Millennium periods of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The Continuous Wavelet Transform (CWT) was em- ployed to determine the dominant variability scales in the dendroclimatic proxies in the regions of Bolivia in the southern Amazon and Rio Paru in the eastern, the Quelccaya ice core and the Reconstructed Niño 3.4 Index in the common period of 1799-1990. These time series were also employed to validate the Palmer Drought Severity Index (PDSI) and the simulated Niño 3.4 indices from the Sea Surface Temperature Anoma- lies (SSTA) and Air Temperature Anomalies (AT2M) of the Last Millennium Reanalysis (LMR) and Paleo Hydrodynamics Data Assimilation Product (PHYDA) paleoclimatic simulations. The dominant spatial-temporal patterns of ENSO in the Last Millennium in the paleoclimatic simulations were found through the application of Empirical Orthog- onal Functions (EOF) in the Tropical Pacific area. The dominant variability scales of the resulting Principal Components (PC1s) were also analysed with the CWT, while the Quelccaya ice core and Niño 3.4 were used to validate the PC1s. Extreme ENSO events were selected by a percentile threshold of each PC1s in the periods of MCA and LIA, where positive (negative) events were those that were above (below) the 95% (5%) percentile. Spatial correlation fields show an statistical independence between the dendroclimatic proxies and the PDSI indices of all simulations, but it was shown that the Quelccaya ice core and the Reconstructed Niño 3.4 Index configure signifi- cant ENSO patterns in the Tropical Pacific. In the Last Millennium, the dominant EOF modes (EOF1) reveal that ENSO was the dominant mechanism of interannual climate variability in all the simulations. There are spectral differences among the PC1s but a considerable dominance of decadal to multidecadal scales was found during LIA for all time series except the LMR PC1. The higher frequency and intensity of extreme events suggest a higher ENSO activity during this period, with profound implications for the Amazon’s climate variability not only in the past but for future scenarios of climate change as well. The results indicate that extreme drought and floods in the Basin were more intense during LIA, but those events could have been significantly influenced by interactions between the ENSO and the Tropical Atlantic which worked to amplify and damp them as well.