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Recent studies have shown that global warming and associated sea-surface temperature (SST) changes may trigger an important rainfall increase in southeastern South America (SESA) during the austral summer (December-January-February, DJF). The goal of this paper is to provide some insight into processes which may link global and SESA changes. For this purpose, a 'two-way nesting' system coupling interactively the regional and global versions of the LMDZ4 atmospheric model is used to study the response to prescribed SST changes. The regional model is a variable-grid version of the global model, with a zoom focused over South America. An ensemble of simulations forced by distinct patterns of DJF SST changes has been carried out using a decomposition of full SST changes into their longitudinal and latitudinal components. The full SST changes are based on projections for the end of the twenty-first century from a multi-model ensemble of WCRP/CMIP3. Results confirm the presence of a major rainfall dipole structure, characterized by an increase in SESA and a decrease in the South Atlantic Convergence Zone region. Rainfall changes found in the WCRP/CMIP3 models are largely explained as a response of this dipole structure to the zonally-asymmetric (or longitudinal) component of SST changes. The rainfall response to the zonal-mean (or latitudinal) SST changes (including the global warming signal itself) shows an opposite contribution. The processes explaining the role of zonally-asymmetric SST changes involve remote effects of SST warming over the equatorial Indian and Pacific oceans inducing an atmospheric wave-train extended across the South Pacific into South America. [ABSTRACT FROM AUTHOR]

This paper examines the records of streamflow during the period 1901--95 corresponding to four major rivers in southeastern South America: Uruguay, Negro, Parana, and Paraguay. The emphasis is on the detection of long-term trends in the records. The authors demonstrate that the 30-yr running averaged streamflows increased after the mid-1960s at a rate that is approximately linear but not the same in all rivers. There seems to be a tendency toward leveling off in the most recent values. The increased streamflow is consistent with a significant decrease in the amplitude of the seasonal cycle in all rivers, except in the Negro River. An analysis of the sea surface temperature in the eastern equatorial Pacific Ocean suggests that an important component of such an increase in streamflows is consistent with a large-scale and low-frequency variability of the climate system. [ABSTRACT FROM AUTHOR]

Recent improvements in satellite altimetry data correction terms are encouraging studies of the remote sensed sea level anomalies (SLA) progressively closer to the coast and over shallow continental shelves. In this paper we describe and discuss the SLA trend and variability at seasonal and interannual time scales in the southeastern South American continental shelf influenced by the Río de la Plata estuary and the Patos Lagoon fresh waters. The spatio-temporal coverage of the gridded altimetry SLA data allows identify several variability patterns and the associated physical processes. On seasonal time scales, the combination of the solar radiation and wind forcing cycles accounts for up to 98% of the variability. Seasonal variability of the wind is responsible for a difference of up to 16 cm between the southern (Argentinean) Río de la Plata estuary coast and the Uruguayan and southern Brazilian coasts. On interannual time scales, positive/negative SLA anomalies are coherent with El Niño/La Niña events. Finally, a significant positive trend of up to 5 mm yr −1 is found in all the study area except in the region around the Patos Lagoon (Brazil) and part of the Río de la Plata. Besides the local relevance of the results, this study indicates that satellite altimetry data are accurate enough to unveil SLA spatio-temporal patterns close to the coast and over continental shelves in the mentioned time scales. [ABSTRACT FROM AUTHOR]

Southwestern South America (SWSA) has undergone frequent and persistent droughts in recent decades with severe impacts on water resources, and consequently, on socio-economic activities at a sub-continental scale. The local drying trend in this region has been associated with the expansion of the subtropical drylands over the last decades. It has been shown that SWSA precipitation is linked to large-scale dynamics modulated by internal climate variability and external forcing. This work aims at unravelling the causes of this long-term trend toward dryness in the context of the emerging climate change relying on a large set simulations of the state-of-the-art IPSL-CM6A-LR climate model from the 6th phase of the Coupled Model Intercomparison Project. Our results identify the leading role of dynamical changes induced by external forcings, over the local thermodynamical effects and teleconnections with internal global modes of sea surface temperature. Our findings show that the simulated long-term changes of SWSA precipitation are dominated by externally forced anomalous expansion of the Southern Hemisphere Hadley Cell (HC) and a persistent positive Southern Annular Mode (SAM) trend since the late 1970s. Long-term changes in the HC extent and the SAM show strong co-linearity. They are attributable to stratospheric ozone depletion in austral spring-summer and increased atmospheric greenhouse gases all year round. Future ssp585 and ssp126 scenarios project a dominant role of anthropogenic forcings on the HC expansion and the subsequent SWSA drying, exceeding the threshold of extreme drought due to internal variability as soon as the 2040s, and suggest that these effects will persist until the end of the twenty-first century. [ABSTRACT FROM AUTHOR]

The Notothenioidei are a typical example of stenothermal fishes since most species have evolved and lived in Antarctic waters, where the water temperature is low and stable. This fact enabled them to evolve physiological characteristics related to cold. Nevertheless, some species came out of Antarctic waters a few million years ago and coped with more variable thermal regimes. This work aims to determine the thermal tolerance and preference of two sub-Antarctic notothenioid species found in Southern South America, Patagonotothen tessellata and Harpagifer bispinis, adding valuable information about thermal adaptation mechanisms. Experiments were conducted after exposing their juveniles for three weeks at 4, 7, 10 and 12 °C. Their thermal tolerance limits were established using the Critical Thermal Methodology and their acute thermal preferenda, employing a horizontal thermal gradient tank. Fishes acclimated to different exposure temperatures had small to intermediate thermal tolerance polygons (P. tessellata: 593.85°C2, H. bispinis: 475.40 °C2) and positive relationships between preferred and acclimation temperatures. The Final Temperature Preferenda were estimated to be 14.25 °C for P. tessellata and 13.05 °C for H. bispinis, allowing to characterize them as cold eurythermal species, with P. tessellata more tolerant to heat and H. bispinis more tolerant to cold. Their different thermal sensitivities are in agreement with their different thermal histories and distributions. In a climate change context, the increase of sea surface temperatures is likely to reduce the northern boundaries of their distributions. Conversely, it can potentially enhance both species' performances at their southernmost distribution limits since those environments are cooler than their maximum thermal tolerances. [ABSTRACT FROM AUTHOR]

ABSTRACT The 1976-1977 cold-to-warm sea surface temperature ( SST) shift in the tropical Pacific Ocean, which has been associated with a phase change of the Pacific Decadal Oscillation ( PDO) index, separated a 'La Niña-like' decadal regime from an 'El Niño-like' one. In this article, we analyse the differences of mean of annual and austral-summer ( DJF) temperature, precipitation, and sea-level pressure ( SLP) over South America ( SA) between 1961-1973 and 1978-1990, and explore the occurrence of significant shifts in their time series. Our sources are instrumental records, gridded interpolated data, and reanalyses. Although major regional differences in the intensity of the signal are detected, the climate shift is identified in all variables. In the mid-1970s at annual level, reanalysis SLP data reveal the onset of a step-like anticyclonic circulation anomaly in the southern tip of SA and an abrupt weakening of the Southeast Pacific Subtropical Anticyclone ( SEPA). This latter feature may have partly induced the rapid warming observed along the tropical-extratropical west coast of the continent through the weakening of the cold Humboldt current system. An abrupt warming was also detected in surface air temperature ( SAT) composites located along the coast of the northern part of SA and in Southeastern SA ( SESA). During summer, we found a particularly conspicuous shift-like warming over Southern South America ( SSA, comprising Patagonia). Besides, a shift-like increase (decrease) in annual mean precipitation is observed over Central Argentina and in the tropics, to the south (north) of 10°S. In line with previous studies, we conclude that both the interannual (El Niño-Southern Oscillation, ENSO) and the interdecadal ( PDO) variability modes seem to have had an incidence in the manifestation of the 1970s climate shift, and that its magnitude appears to be unprecedented during the 20th century, as shown in particular by century-long SAT composites from northern Chile and SSA. [ABSTRACT FROM AUTHOR]

Spatially precise forecasts of the impacts of climate change on the distribution of major vegetation types are essential for the implementation of effective conservation and land use policy. However, existing studies frequently omit major sources of climate variability that can significantly increase the uncertainty of projections. In this study we demonstrate how different predictions for sea surface temperature (SST) for the first half of the twenty-first century increase the uncertainty associated with forecasts of the future distribution of major ecosystems in South America. This is demonstrated through a numerical experiment using a coupled climate-vegetation model (CCM3-IBIS) for IPCC emission scenario A2 that incorporates the SST data from ten different models. The study reveals an increasing uncertainty in the ability to forecast future vegetation patterns, such that by 2050 the simulation is unable to robustly forecast the vegetation cover in an area equivalent to 28 % in South America (5 × 10 km). The future of the central and northeastern regions of Brazil is especially uncertain, with outcomes, ranging from savanna, and open shrubland to grassland. Recognizing and managing such uncertainty should be a priority for decision makers. [ABSTRACT FROM AUTHOR]