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Despite current state-of-the art global climate model (GCMs) ability to simulate well the large scale state of the global climate, there is significant variation in future climate projections of precipitation and temperature changes in South America. In order to adequately assess the possible impacts and national vulnerabilities of climate changes, full consideration of these variations in projections is of vital importance. As a starting point for this, here we use a large ensemble of simulations with the HadCM3 climate model, where each ensemble member incorporates different but plausible versions of the parameterisations of important physical processes, is used to assess the potential impact of climate change on precipitation and temperature over South America and explore the uncertainties associated with the various model parameterisations. Particular attention is paid to the general seasonal characteristics, for example the South Atlantic Convergence Zone which modulates summer rainfall over most of the continent. The changes simulated with the Eta regional model forced with of these GCM ensemble members are also reported.

An overview of the international PIRATA project over the tropical Atlantic and its impacts on the development of basin scale oceanographic research in Brazil are presented. In a nutshell, the PIRATA project is a consortium between Brazil, France and the United States for the establishment of a moored research array over the tropical Atlantic to monitor the ocean-atmosphere interface and the upper layer of the ocean. The array was designed to study the principal modes of interannual variability of the tropical Atlantic climate, namely the equatorial and the meridional modes. PIRATA data have been used by many, with more than 300,000 data files distributed via internet during the last ten years, with 97,000 files distributed in 2008 alone. The array was inaugurated with 12 ATLAS moored buoys along the equator and the meridians 38W and 10W in 1998, and grew into a 18 moored systems (see Figure 1) after the establishment of the SW extension in 2005 and the NE extension in 2008. In addition to the surface meteorological and upper ocean data measured by the ATLAS systems, the PIRATA project also counts with one ADCP mooring at 0N, 23W, tide gauges at São Tomé and Prince, and at Saint Peter and Saint Paul archipelago, in addition to pig backing sensors to monitor CO2 and O2, also indicated in Figure 1. In addition, the PIRATA array yearly maintenance cruises, done by each of Brazil, France, and the USA, have been used as a platform of opportunity to collecting extra atmospheric and oceanographic data. Such time series constitute an extremely valuable body of information from sparse oceanic data areas, which have been used to generate a growing number of research papers in the specialized literature. More than 85 papers have been published so far using PIRATA data during the last ten years. In Brazil, the PIRATA project has galvanized the interest of an expanding community of researchers and has contributed to increase the support from funding agencies. The uses of PIRATA data time series have also been instrumental in the country for both: ocean and coupled ocean-atmosphere model validation studies, and real time monitoring of Tropical Atlantic oceanic conditions relevant for seasonal climate predictions over Brazil. This talk also presents the Brazilian efforts to developing its global climate model, for which both physical and biogeochemical measurements done at the PIRATA array and during the oceanographic cruises are vital.

The dominant modes of coupled ocean-atmosphere variability of the Tropical Atlantic are investigated using observational data, focusing on the cold tongue mode. The seasonal evolution and interannual variability of each mode is obtained from a joint EOF analysis of the three elements of the Bjerknes feedback, using wind speed in the western basin, and sea surface temperature (SST) and depth of the 20C isotherm from the easternmost Tropical Atlantic. Results agree with previous studies, confirming the robustness and seasonality of the positive Bjerknes feedback. The analysis reveals a dominant mode of variability remotely forced by El Nino–Southern Oscillation (ENSO) after 0–12 months, with smaller amplitude due to a limited feedback between SST and the wind speed. The second mode represents the local ocean–atmosphere interaction of the Tropical Atlantic basin, and is characterized by a strong positive feedback and a larger amplitude. Both modes are stronger during boreal summer.

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid-and high-latitudes, (2) a strong function of dryness at mid-and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45 degrees N). The sensitivity of NEE to mean annual temperature breaks down at similar to 16 degrees C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence.

Neste trabalho são analisadas as mudanças no padrão de circulação que possam vir a acontecer no clima da América do Sul (AS), como conseqüência do aumento nas concentrações dos gases de efeito estufa. Para isto utilizam-se cinco modelos globais do IPCC AR4 (CCCMA, GFDL, HadCM3, MIROC e GISS), para o clima do século XX (1961-1990 – 20C3M) e para o cenário futuro SRES_A2 (2011-2100). As características em comum que os modelos apresentaram (a exceção do MIROC) para as três climatologias futuras (2011-2040, 2041-2070 e 2071-2100), principalmente, no verão e na primavera, foram o deslocamento da baixa continental (associada à baixa do Chaco) para o sudoeste da sua posição climatológica (1961-1990), e da Alta da Bolívia para o noroeste. Além disso, os cinco modelos simularam, para o clima presente, uma Alta do Pacífico Sul (APS) menos intensa em relação à Reanálise do NCEP, sugerindo menor subsidência sobre a sua região de atuação. Para cenários futuros os modelos GISS e HadCM3 simularam a APS menos intensa. Por outro lado, para a alta do Atlântico Sul, não existiu um consenso nos modelos. Em geral foi simulada mais intensa (a exceção do GISS), sobretudo no outono e no inverno. O modelo HadCM3 simulou a circulação de verão e primavera mais próxima à Reanálise, com uma ZCAS melhor definida, e uma área menor de anomalias negativas de chuva sobre a Amazônia, em relação aos outros modelos. Já para o cenário futuro este modelo modificou seu padrão de chuvas, e anomalias positivas, sobre a costa norte do Peru e Equador, e negativas sobre o Nordeste e leste da Amazônia, foram observadas, associadas a uma APS enfraquecida e deslocada para o sul, o que reforçou a ZCIT do Pacífico sobre 5°S. Uma diminuição da convergência de umidade sobre a Amazônia também foi observada.

Conserving natural vegetation cover is of critical importance for maintaining the ecological integrity and hydrological properties of large river basins (more than 100 000km2). Recent estimates indicate that more than 700 000km2 of Brazilian Amazon have already been deforested, and to reduce further losses and preserve the important natural and cultural resources in this region, large conservation areas have been created by the Brazilian government. The present study analysed land cover and land use change in the major watersheds of the Brazilian Amazon, in order to evaluate the current balance between deforestation and conservation of natural areas in the region. The results show that watersheds draining the southern part of the basin have suffered the highest deforestation rates, with the largest losses (8.320% of total basin area) occurring in the Madeira, Tapaj´os, Xingu, Araguaia and Tocantins river basins. Most largewatersheds already have significant deforestation in their headwaters, which can affect hydrological functions and ecological sustainability. The greatest allocation of land for conservation was encountered in the Trombetas, Xingu and Negro watersheds, where conservation areas occupied 92.5, 56.9 and 50.6% of the total basin, respectively. While extensive areas of the Amazon biome have been deforested, on the scale of large watersheds there is a positive balance between conservation areas and deforestation, and on average the area delimited by conservation areas is more than three times larger than the deforested areas. An analysis by subwatersheds, however, indicates that certain regions have achieved more critical levels of deforestation, in some situations affecting more than 80% of the subwatersheds.

Hydroelectric reservoirs generate energy without significant combustion of fossil fuels. However, these systems can, potentially, emit greenhouse gases (GHGs) at a rate which may be significant at the global scale, and, possible, co-equal, per kilowatt-hour, to that from conventional coal or oil-fired systems. Although much of the new construction of hydroelectric reservoirs is in the tropics, most of the data on GHG emissions comes from temperate regions. Further, much of the existing data on reservoir gas emissions comes from single sites, usually near the terminal dams. Large tropical reservoirs often involve the impoundments of river systems with complex morphology which in turn can cause spatial heterogeneity in gas flux. We evaluated spatial and seasonal variability in CO2 concentrations and gas flux for five large (50 1,400 km2) reservoirs in the Cerrado region of Brazil. Most of data set (87% of all measurements) showed CO2 supersaturation and net efflux to the atmosphere. There was as much or more variation in pCO2 over space and among seasons. The large studied reservoirs showed different zones in terms of CO2 emission because those fluxes are dependent on flooded biomass, watershed input of organic matter and dam operation regime. Here we demonstrate that the reservoirs in the Brazilian Cerrado have low rates of CO2 emissions compared to existing global comparisons. Our results suggest that ignoring the spatial variability can lead to more than 25% error in total system gas flux.