Publicações

A precipitação é um dos principais fatores que determina a dinâmica sazonal da vegetação na região de savanas tropicais, como é o caso do cerrado brasileiro. Neste trabalho foram analisadas as relações da precipitação sazonal, com o comportamento sazonal das classes de uso e cobertura da terra (UCT), principalmente as fisionomias de cerrado do Estado de Tocantins. Foi analisada a dinâmica sazonal do cerrado, incluindo áreas florestadas e não florestadas, a partir da análise de imagens do MODIS/TERRA IV (Índices de Vegetação) de janeiro a dezembro de 2004, bem como dados diários de precipitação de 2004 e uma série de precipitação diária do período de 1969 a 2005. Os resultados da análise de precipitação mostram que a área de estudo apresentou uma alta sazonalidade, com estação seca de maio a setembro. As análises dos IV mostram que a dinâmica sazonal das formações de cerrado é similar àquela das áreas convertidas para outros usos. O padrão sazonal das classes de UCT segue os padrões da precipitação, cujos menores valores foram registrados no mês de agosto de 2004, mês este que apresentou os menores valores dos IV. Diferentemente das demais classes de UCT, a formação florestal não se ajustou ao padrão de precipitação, apresentando valores de IV similares ao longo do ano com leve decréscimo no mês de setembro de 2004. ABSTRACT: Precipitation is one of the main factors that determine the seasonal dynamics of the vegetation in tropical savanna areas, as the Brazilian cerrado. In this work the relationship of the seasonal precipitation with the seasonal behavior of the land use and land cover (LULC) types, mainly savannah physiognomies of the Tocantins State, was investigated. We analyzed the savanna seasonal dynamics, including forest and converted areas, with MODIS/TERRA VI (vegetation indexes) satellite measurements from January to December 2004 and daily precipitation of 2004 and daily precipitation series from 1969 to 2005. The results of the precipitation analysis show that the study areas exhibited a high seasonality with a dry season from May to September. The analysis of the VI showed that the seasonal dynamic of the savanna formations and the converted areas were similar. The seasonal pattern of these LULC types follows the precipitation pattern, when the lowest VI values were recorded in August of 2004. Differently of these LULC types, forest formations do not fitted to the precipitation pattern, this LULC type keep similar VI values along year with light decrease in September of 2004.

December to March climatologies of precipitation and vertically integrated water vapor transport were analyzed and compared in order to find the main paths by which moisture is fed to high rainfall regions in the southern hemisphere in this season. The southern tropics (20°S to 0°) exhibit high rainfall and receive ample moisture from the northern trades, except in the eastern Pacific and the Atlantic Oceans. This inter-hemispheric flow is particularly important for Amazonian rainfall, establishing the North Atlantic as the main source of moisture for the forest during its main rainy season. In the subtropics the rainfall distribution is very heterogeneous. The meridional average of precipitation between 35°S to 25°S is well modulated by the meridional water vapor transport through the 25°S latitude circle, being greater where this transport is from the north and smaller where it is from the south. In South America, to the east of the Andes, the moisture that fuels precipitation between 20°S and 30°S comes both from the South and from the North Tropical Atlantic Oceans whereas between 30°S and 40°S it comes mostly from the North Atlantic after passing over the Amazonian rainforest. The meridional transport (across 25°S) curve exhibits a double peak over South America and the adjacent Atlantic, which is closely reproduced in the mean rainfall curve. This corresponds to two local maxima in the two dimensional field of meridional transport: the moisture corridor from Amazonia into the continental subtropics and the moisture flow coming from the southern tropical Atlantic into the subtropical portion of the South Atlantic Convergence Zone. These two narrow pathways of intense moisture flow could be suitably called aerial rivers. Their longitudinal positions are well defined. The yearly deviations from climatology for moisture flow and rainfall correlate well (0.75) for the continental peak but not for the oceanic peak (0.23). The structure of two maxima is produced by the effect of transients in the time scale of days.

By using differential equations, evolutionary game theory shows that most of the games of competition for resources have equilibrium strategies named Evolutionary Stable. Although this approach can deduce these points, it is not possible to say how or whether a population will reach such equilibrium. We present an evolutionary agent-based model where individuals compete for space using mixed strategies. Agents belong to spatial locations that settle with whom they can interact, but they can freely move to contiguous partitions according to a definition of satisfiability. The simulation results show that, although the agents do not have any knowledge about equilibrium points, the populations mean strategy always converges to a stable state, close and above to the analytic equilibrium. Moreover, it is reached independently of the initial population.

By using differential equations, evolutionary game theory shows that most of the games of competition for resources have equilibrium strategies named Evolutionary Stable. Although this approach can deduce these points, it is not possible to say how or whether a population will reach such equilibrium. We present an evolutionary agent-based model where individuals compete for space using mixed strategies. Agents belong to spatial locations that settle with whom they can interact, but they can freely move to contiguous partitions according to a definition of satisfiability. The simulation results show that, although the agents do not have any knowledge about equilibrium points, the populations mean strategy always converges to a stable state, close and above to the analytic equilibrium. Moreover, it is reached independently of the initial population.

Current studies show that reservoirs are responsible for emissions of greenhouse gases (St. Louis et al. 2000, Duchemin et al. 2002, Soumis et al. 2004, Abril et al. 2005, Lima et al. 2008). Surface waters of aquatic ecosystems exhibit supersaturated dissolved CO2 (Cole 1999, Richey et al. 2002) because respiration based on both autochthonous and allocthonous organic carbon usually exceeds primary production (del Giorgio et al. 1997, Cole 1999, Jonsson et al. 2003). Dissolved organic carbon transported to the aquatic ecosystem from the drainage basin usually remains biologically refractory. Upon exposure to sunlight in a relatively well-lit aquatic environment, however, terrigenous organic carbon might undergo photolytic degradation and become more labile (Cole 1999). In spite of photomineralization, carbon dioxide effluxes may also result from methanotrophic activities (Frenzel et al. 1990, Abe et al. 2005, Lima 2005) associated with diel oxygen production via photosynthesis (King 1990, Lima et al. 2005a). Moreover, diel changes in sunlight may also affect dissolved gas solubility and, in particular, surface water density, leading to convection during cooling events (MacIntyre et al. 2001). We evaluated possible roles of sunlight on the daily variability of CH4 and CO2 diffusive fluxes from Corumba reser- ´ voir in Brazil. Our results support that CO2 and CH4 emissions in Corumba are substantially influenced by sunlight- ´ induced processes, although we cannot precisely identify the primary variables inducing diel changes

Land changes are determined by a complex web of biophysical and socio-economic factors that interact in time and space, in different historical and geographical contexts, creating different trajectories of change. It is peopleís response to economic opportunities mediated by institutional factors that drives changes. In this paper we discuss how to incorporate such institutional land tenure categories in land change models. Our hypothesis is that this is an essential step in the direction of constructing regional models to represent the heterogeneity of actors and processes. We implemented the conceptual proposal using the TerraME modeling Environment. Through a case study we analyze how the existence of different rules of territory use affects the landscape dynamics at the regional level.

Land changes are the result of a complex web of interaction between human and biophysical factors, which act over a wide range of temporal and spatial scales. In this paper we conceptualize spatial relations among geographic objects at different scales. We analyze two types of spatial relations: hierarchical, which handles the interaction of nested objects at different scales (countries, states and municipalities, for example); and a network-based relation, which handles action-at-a-distance types of interaction (market chains, for instance) of objects at different scales (such as farms in Central Amazonia to soybean market consumers at the global scale). We implemented such relations in the Terralib environment, in which they can be constructed using selected strategies, and then used in dynamic models. We exemplify the use of such concepts in a real-world case study in the Brazilian Amazonia. We conclude that combining hierarchical and network-based spatial relations provide a comprehensive conceptual framework to include top-down and bottom-up interactions and feedbacks in multi-scale landchange models.

However the spatial resolution of GCMs remains quite coarse , in the order of 300 x 300 km, and at scale , the regional and local details of the climate which are influenced by spatial heterogeneities in the regional physiography are lost. Therefore, there is the need to convert the GCM outputs into a reliable data set with higher spatial resolution, with daily rainfall and temperature time series at the scale of the watershed or a region to which the climate impact is going to be onvestigated. The methods used to convert GCM outputs into local meteorological variables required for reliable climate modeling are usually referred to as downcaling techniques (Hewinton e Crane, 1996).

As Histoty embraces the beginning of a new millennium, old problem still constitute enormous challenges to the popoulation in general, and to the academic world in particular. It is now widely accepted that General Circulation Models (CCMs) represent the most satisfactory technique to answer these challengs (IPCC, 1996). Numerical models (General Circulation Models or GCMs), representing physical processes in the atmosphere, ocean, cryosphere and land surface, are the most advanced tools currently. avaible for simulating the respose of the global climate system ti increasing greenhouse gas concentrations. This work analyses the performance of the IPCC models (CCma, CCSRNIES, CSIRO, GFDL, HACM3, and others) in simulate the present and future climate pattern of the rainfall over the South America Continent. It general the models get to reproduce the phase of the annual cycle of the rainfall. In this work was used four common metric are reviewed, the Heidke skill score, relative operating characteristic (ROC) skill score, equitable threat score, and the rank analog.

Based on analyses of high-speed video recordings of cloud-to-ground lightning in Brazil and the USA, the characteristics of positive cloud-to-ground (+CG) leaders are presented. The high frame rates permitted the average, 2-dimensional speeds of development along the paths of the channels to be resolved with good accuracy. The values range from 0.3 to 6.0 × 105 ms−1 with a mean of 2.7 × 105 ms−1. Contrary to what is usually assumed, downward +CG leader speeds are similar to downward −CG leader speeds. Our observations also show that the speeds tend to increase by a factor of 1.1 to 6.5 as they approach the ground. The presence of short duration, recoil leaders (RLs) during the development of positive leaders reveal a highly branched structure that is not usually recorded when using conventional photographic and video cameras. The existence of the RLs may help to explain observations of UHF-VHF radiation during the development of +CG flashes.

This paper presents a study about the sensitivity of cloud-to-ground (CG) lightning activity to changes in surface air temperature at daily, monthly, yearly, and decadal timescales in the city of São Paulo (Brazil). Lightning data collected in the city by the Brazilian Lightning Detection Network (BrasilDat) from 1999 to 2006 and thunderstorm day data obtained from 1951 to 2006 were analyzed and compared with surface air temperature data. The lightning activity increases significantly with increasing temperature, with a sensitivity of approximately 40% per 1°C for daily and monthly timescales and approximately 30% per 1°C for decadal timescale. For the yearly timescale, the increase is not statistically significant. The lower sensitivity for the decadal timescale suggests that the lightning sensitivity to changes in surface air temperature decreases for larger timescales, in agreement with what is expected on the basis of convective adjustment. The decadal lightning sensitivity found in this study is in reasonable agreement with the increase in the global lightning activity estimated by most climate models. The study is the first to investigate in detail this relationship in a large urban area inside the tropics and should contribute to the effort to understand the impact of the global warming on lightning activity.

We examine relative magnitudes of electric field peaks of first and subsequent return strokes in negative cloud-to-ground lightning flashes recorded in Florida, Austria, Brazil, and Sweden. On average, the electric field peak of the first stroke is appreciably, 1.7 to 2.4 times, larger than the field peak of the subsequent stroke ( except for studies in Austria where the ratio varies from 1.0 to 2.3, depending on methodology and instrumentation). Similar results were previously reported from electric field studies in Florida, Sweden, and Sri Lanka. For comparison, directly measured peak currents for first strokes are, on average, a factor of 2.3 to 2.5 larger than those for subsequent strokes. There are some discrepancies between first versus subsequent stroke intensities reported from different studies based on data reported by lightning locating systems (LLS). The ratio of LLS-reported peak currents for first and subsequent strokes confirmed by video records is 1.7 to 2.1 in Brazil, while in the United States ( Arizona, Texas, Oklahoma, and the Great Plains) it varies from 1.1 to 1.6, depending on methodology used. The smaller ratios derived from the LLS studies are likely to be due to poor detection of relatively small subsequent strokes. The smaller values in Austria are possibly related ( at least in part) to the higher percentage ( about 50% versus 24-38% in other studies) of flashes with at least one subsequent stroke greater than the first. The effects of excluding single-stroke flashes or subsequent strokes in newly formed channels appear to be relatively small.