The Pacific Interdecadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) influence in different ways the La Niña (LN) related teleconnections in South America. The low‐frequency backgrounds in the Atlantic and Pacific Oceans play an important role in modulating the LN‐related Walker and Hadley cells and the Rossby wavetrain pattern in the Southern Hemisphere. The illustration shows the LN‐related SST anomaly pattern during the austral summer for distinct low‐frequency backgrounds.This analysis investigates the concomitant influence of two dominant low‐frequency modes, the Pacific Interdecadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO), on the La Niña (LN) related climate teleconnections over South America (SA). Four possible low‐frequency backgrounds are analysed: WAMO/WPDO, WAMO/CPDO, CAMO/WPDO and CAMO/CPDO, with the letters “W” and “C” referring, respectively, to the warm and cold phases of the AMO and PDO. The low‐frequency anomalous sea surface cooling (warming) in the tropical Pacific during the CPDO (WPDO) favours (impedes) the settling of the LN‐related negative SST anomalies in this oceanic sector. Thus, the LN‐related SST anomaly patterns in the tropical Pacific in the CPDO backgrounds are meridionally more extensive and stronger than those in the WPDO backgrounds. The highest and lowest percentages of the years that experienced LN events occurred during the WAMO/CPDO and CAMO/WPDO backgrounds, respectively. The northern node of the LN‐related wet–dry dipole between northern SA and southeastern SA (SESA) occurs in most seasons for all backgrounds. However, the southern node occurs in specific seasons: spring and summer for the WAMO/WPDO, winter and spring for the WAMO/CPDO, winter and summer for the CAMO/WPDO and spring for the CAMO/CPDO. Also, the LN effect on the South American monsoon with a wet–dry dipole between northern SA and eastern Brazil during summer is noted in most backgrounds, but with differences among them. We discuss here the differences in the precipitation anomaly patterns, Walker and Hadley cells and Rossby wavetrain patterns among the backgrounds. The low‐frequency Atlantic and Pacific backgrounds play an important role in defining the rainfall anomaly pattern associated with the LN. The results shown here have not been discussed before and might be useful mainly for climate monitoring purposes.

This paper examines the oceanic mean states associated with the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) and their relations to the El Niño (EN). The mean states refer to the simultaneous occurrences of warm (W) and cold (C) phases of these oscillations: WAMO/CPDO, CAMO/WPDO and CAMO/CPDO. In general, the sea surface temperature (SST) anomaly patterns of the mean states show a combination of the PDO and AMO related anomaly patterns in the Pacific Ocean, and the strongest AMO‐related anomaly signals in the Atlantic Ocean with almost antisymmetric SST anomaly patterns in the northern and southern extratropical sectors of this Ocean. One of the most important results of this paper concerns the contrasting features between the CAMO/WPDO and the WAMO/CPDO mean states, which are noticeable for the SST, zonal circulation cell and precipitation during the austral autumn. Besides the opposite inter‐basin equatorial Atlantic/eastern equatorial Pacific cells, the CAMO/WPDO and WAMO/CPDO mean states also feature, respectively, a weakened and strengthened Walker cell in the tropical Pacific during the austral autumn. The results here indicate that the inter‐basin east–west cell between the equatorial Atlantic and eastern Pacific contributes to strengthen (weaken) the Walker cell during the austral autumn of the WAMO/CPDO (CAMO/WPDO) mean state. We also found that the mean states alter the EN features. The EN‐related largest positive SST anomalies occur in the central tropical Pacific during the WAMO/CPDO, and in the eastern tropical Pacific during the CAMO/WPDO. The Atlantic and Pacific oceanic mean states play an important role in modulating the EN features and their effects on the South American rainfall. The results presented in this paper might be relevant for climate monitoring and modelling studies.

A better understanding of the relative roles of internal climate variability and external contributions, from both natural (solar, volcanic) and anthropogenic greenhouse gas forcing, is important to better project future hydrologic changes. Changes in the evaporative demand play a central role in this context, particularly in tropical areas characterized by high precipitation seasonality, such as the tropical savannah and semi-desertic biomes. Here we present a set of geochemical proxies in speleothems from a well-ventilated cave located in central-eastern Brazil which shows that the evaporative demand is no longer being met by precipitation, leading to a hydrological deficit. A marked change in the hydrologic balance in central-eastern Brazil, caused by a severe warming trend, can be identified, starting in the 1970s. Our findings show that the current aridity has no analog over the last 720 years. A detection and attribution study indicates that this trend is mostly driven by anthropogenic forcing and cannot be explained by natural factors alone. These results reinforce the premise of a severe long-term drought in the subtropics of eastern South America that will likely be further exacerbated in the future given its apparent connection to increased greenhouse gas emissions.

Oceanic-atmospheric phenomena of different time scales concurrently might affect the streamflow in several basins around the world. The Atrato River Basin (ARB) and Patía River Basin (PRB) of the Colombian Pacific region are examples of such basins. Nevertheless, the relations between the streamflows in the ARB and PRB and the oceanic-atmospheric factors have not been examined considering different temporal scales. Hence, this article studies the relations of the climate indices and the variability of the streamflows in the ARB and PRB at interannual and decadal timescales. To this, the streamflow variability modes were obtained from the principal component analysis (PCA); furthermore, their linear dependence with indices of the El Niño/Southern Oscillation (ENSO), precipitation (PRP), the Choco low-level jet (CJ), and other indices were quantified through (a) Pearson and Kendall’s tau correlations, and (b) wavelet transform. The PCA presented a single significant mode for each basin, with an explained variance of around 80%. The correlation analyses between the PC1s of the ARB and PRB, and the climate indices showed significant positive (negative) high correlations with PRP, CJ, and Southern Oscillation Index (SOI) (ENSO indices). The wavelet coherence analysis showed significant coherencies between ENSO and ARB: at interannual (2–7 years) and decadal scale (8–14), preferably with the sea surface temperature (SST) in the east and west Tropical Pacific Ocean (TPO). For PRB with the SST in the central and western regions of the TPO in the interannual (4–8 years) and decadal (8–14 years) scales, the decreases (increases) in streamflow precede the El Niño (La Niña) events. These results indicate multiscale relations between the basins’ streamflow and climate phenomena not documented in previous works, relevant to forecast the extreme flow events in the Colombian Pacific rivers and for planning and implementing strategies for the sustainable use of water resources in the basins studied.

This study examines the influence of the Atlantic Multidecadal Oscillation (AMO) on the Choco Low-level Jet (CJ) variations during the 1983–2016 period. Considering the September–November (SON) 925 hPa zonal wind index in the CJ core, a significant breakpoint occurs in 1997 with larger values after 1997. The changes in the CJ and Caribbean Low-Level Jet (CLLJ), and their related ocean-atmospheric patterns and impacts on precipitation over Colombia were analyzed considering separately the 1983–1996 and 1998–2016 periods, which overlap the cold and warm AMO phases, respectively. During the 1998–2016 period, the negative sea surface temperature (SST) anomalies in the tropical Pacific Ocean and the positive ones in the Caribbean Sea and Tropical North Atlantic (TNA) strengthen the CJ and weaken the CLLJ, and moisture is transported into Central and Western Colombia increasing the rainfall there. Our results indicate that part of the CJ strengthening after 1997 was due to a higher percentage of intense CJ events coinciding with La Niña events during the warm AMO and cold Pacific Decadal Oscillation (PDO) background. However, the AMO-related SST and sea level pressure (SLP) variations in the TNA seem to be more crucial in modulating the CJ and CLLJ intensities, such that CJ is weakened (intensified) and CLLJ is intensified (weakened) before (after) 1997. As far as we know, the relations of the CJ and CLLJ intensities to the AMO phases were not examined before and might be useful for modeling studies.