Publicações

We examine potential critical thresholds for biome shift in the Amazonian tropical forest by forcing a potential vegetation model with prescribed climate anomalies and projections from global and regional climate models and different levels of CO2 fertilization effect under the SRES A2 scenario (2070-2099). The results indicate that tropical forests might be replaced by seasonal forests or savanna over eastern Amazonia with temperature increases of 2-3 degrees C (4-5 degrees C), when CO2 fertilization effect is not considered (partially considered), depending on precipitation anomaly. A precipitation decrease greater than 30% would trigger the shift from tropical forest to drier biomes, such as savanna and shrubland in southeastern Amazonia. The projected decrease in precipitation during the dry season and the increase of temperature are the main mechanisms driving calculated biome changes. However, biome changes are considerably smaller when the optimum fertilization effect is included.

This paper examines the constraints that limit the large-scale adoption of open source GIS. Although the open source GIS community has already achieved relevant results, their products have a small market share. There is equivalent to Linux and Apache in the open source GIS scene. We try to explain why this happens, by considering some factors that control the evolution and adoption of open source software. Our view is that the community effort is split in many different systems, not allowing a dominant solution to come forth. Thus, none of the current open source GIS has the potential to be a disruptive technology. Then, we consider a future scenario where most public geospatial data will be available as open access policy. This scenario is becoming more probable given recent data policy decision in Europe, USA and other countries. In this scenario, there is a major chance for a disruptive open source GIS to appear.

Forest to pasture conversion can lead to a decrease of precipitation induced by the decrease of evapotranspiration starting a positive feedback in the climate system. The accelerated deforestation rate suffered by Amazonian region is of global concern due to the importance of the Amazonia to the climate. Improve the understanding of the impact of deforestation in the hydrological cycle is of the highest importance. Nowadays, Amazonian landscape is no longer a homogeneous surface of pristine primary forest, but an heterogeneous irregular patches of pasture and agriculture plots of various sizes. Besides this, those patches were many times abandoned, creating opportunities for the regrowth of original vegetation (secondary forests). Impacts of fragmentation, and more specifically natural regrowth, on regional climate and hydrology are not well known. Previous studies pointed that the conversion of primary forest to pasture or agricultural crops affect the precipitation and runoff, and consequently evapotranspiration at micro scales, but this effect is not always detected at larger temporal and spatial scales. Few works suggested that the evaporative fraction of the secondary forest increases with the age of the forest in comparison with mature primary forests. Therefore, the objective of this study was to compare the evapotranspiration of one site of primary forest with one site of ~20 years old secondary forest in Central Amazonia, and to evaluate whether the secondary forest has a role on the resilience of the Amazon system compensating the effects of the deforestation on the water cycle. The latent heat flux of the secondary forest during the dry season was 29% higher than in the primary forest. During the wet season the secondary forest also presented 17% higher latent heat flux than in primary forest. The values of evapotranspiration were 4.28 mm day-1 for secondary forest against 3.32 mm day-1 for primary forest during the dry season, which represents a difference of around 1 mm day-1. During the wet season, the evapotranspiration for secondary forest was 3.99 mm day-1 against 3.42 mm.day-1 for primary forest, resulting in a difference of around 0.57 mm day-1. The evaporative fraction during the dry season in the secondary forest was around 0.80 and in the primary forest was 0.70. During the wet season this difference was lower, 0.89 for secondary forest and around 0.82 for primary forest. These results show that the difference on energy available for evapotranspiration is not the only cause of the higher evapotranspiration of the secondary forest in comparison with the primary forest in both dry and wet seasons. In conclusion, our study demonstrate that the secondary forest may play a relevant role in the Amazonia system, and confirm the urgent need of a better understanding of the role of this type of vegetation on a basin wide water and energy balance. Additionally, improvement of the representation of secondary vegetation on atmospheric models and in the analysis of soil-water-atmosphere interaction studies at regional and global scales.

A região do semi-árido nordestino brasileiro apresenta sérios problemas ambientais, entre os quais se destacam os processos de desertificação. Sendo assim, o objetivo deste estudo consiste em avaliar as mudanças de cobertura da terra em uma área de desertificação: o Núcleo de Desertificação de Gilbués, Estado do Piauí, Brasil. A análise engloba o período entre 1999 e 2009, e busca, além de avaliar as alterações ocorridas, identificar possíveis fatores do meio físico responsáveis pela dinâmica do processo de desertificação, como precipitação e pedologia. Para este estudo considerou-se imagens do satélite Landsat, sensores TM e ETM+, e estimativas de precipitação da plataforma TRMM (Tropical Raifall Measuring Mission). Além disso, foram utilizados mapas pedológicos, desenvolvidos pela EMBRAPA. A avaliação das alterações das classes de cobertura da terra mostrou que as áreas de cerrado sofreram uma redução de 9%, o equivalente a 550 km2 . O cerrado cedeu lugar às atividades agropecuárias e às áreas de desertificação, que sofreram um aumento de 5% (315 km2) e 4% (240 km2 ), respectivamente. As demais classes, como floresta perene, corpos dágua, área urbana e estradas permaneceram constantes. A precipitação na região variou entre 1.000 mm no setor sudeste e 1.300 mm no noroeste, concentradas essencialmente no verão, entre dezembro e fevereiro. Em relação à variabilidade interanual da precipitação, verificou-se que os eventos de secas ocorreram em anos de El Niño. O crescimento da classe agropecuária está associado às classes de precipitação no intervalo de 1100 a 1250 mm e com as áreas de ocorrência de Latossolo Amarelo. Observou-se associação entre a expansão da agropecuária e tipos de solo; no entanto, o mesmo não aconteceu com a precipitação. As áreas de solo exposto expandiram-se proporcionalmente de acordo com os intervalos de precipitação e com as classes de solos.

Este trabalho tem por objetivo avaliar o desempenho dos índices de vegetação NDVI (Normalized Difference Vegetation Index), EVI (Enhanced Vegetation Index) e LSWI (Land Surface Water Index) na região do Pantanal, considerando os principais tipos de cobertura da terra e os aspectos sazonais da precipitação. Para isso, foram utilizados dados do sensor MODIS, produto MOD13Q1, e estimativas mensais de precipitação do satélite TRMM, produto 3B43. As análises foram feitas por meio de transectos ao longo das regiões, utilizando como referência o mapa de cobertura da terra compatibilizado com as classes de vegetação e usos considerada no modelo de superfície SSiB (Simplified Simple Biosphere Model). Os resultados mostraram que, na estação seca, o NDVI tende a apresentar os maiores valores, entre 0,4 e 0,8; enquanto o LSWI ficou entre 0,0 e 0,4, exceto para a classe Floresta Perene. O EVI apresentou valores intermediários, entre 0,2 e 0,6. Todos os índices mostraram baixa correlação com a precipitação na estação seca, inferiores a 0,25. Na estação chuvosa, o NDVI registrou os maiores valores em quase toda a extensão dos transectos, variando entre 0,6 e 0,8. Apenas em alguns setores da classe Floresta Perene, os valores de LSWI foram superiores ao NDVI. O EVI, em geral, mostrou os valores mais baixos entre os índices, entre 0,2 a 0,5. O LSWI apresentou valores intermediários entre o NDVI e o EVI, de 0,2 a 0,7. Nas classes Cerrado e Chaco, os índices LSWI e EVI ficaram bastante próximos, alternando-se por vezes. O NDVI e o LSWI mostram correlações significativas com a precipitação (α = 5%) em todas as classes de cobertura. Em relação à amplitude (diferença entre máximos e mínimos), o LSWI apresentou a maior variação em todas as classes e, em ambas as estações. O LSWI mostrou-se mais adequado para estudos na região do Pantanal, por captar melhor as variações da vegetação, especialmente no Cerrado e Caatinga na estação chuvosa; e Floresta Perene na estação seca.

This paper presents the evaluation of gaussian models of air quality AERMOD and ISC, highly used for regulatory purposes. The study area was Nova Iguaçu city and the period considered was the summer of 2002. For the simulations we considered the emission of SO2 pollutant from 24 stationary sources and 22 mobile sources in the simulations represented by area and line sources respectively. The model results were compared, in order to examine the best performance for their applications. The analysis was performed with statistical indices recommended in the literature for evaluating air quality models.

Deforestation of tropical forests for logging and agriculture, associated to slash-and-burn practices, is a main contributor of CO2 emissions, both immediate due to biomass burning and future due to the elimination of a potential CO2 sink. Moreover, climate change in the Amazon during the 21st century is projected to decrease the resilience of the Amazon forest and possibly replace large parts of tropical forests with savannas, adding to the direct anthropogenic deforestation. The potential feedbacks between LUCC (Land-Use and Land-Cover Change) and climate change are thought to further increase the loss of tropical forests and increase the rate of CO2 emissions, through mechanisms such as land and soil degradation and the increase in wildfire occurrence and severity. However, current understanding of the processes of fires (including ignition, spread and consequences) in tropical forests and feedbacks with climate are poorly understood and need further research. As the processes of LUCC and associated fires occur at local scales, linking them to large-scale atmospheric processes requires a means of up-scaling higher resolutions processes to lower resolutions. Our approach is to couple models which operate at various spatial and temporal scales: a Global Climate Model (GCM) (and possibly a Regional Climate Model; RCM), Dynamic Global Vegetation Model (DGVM) and local-scale LUCC model and fire behavior model. The climate model(s) resolve larger scale atmospheric processes and forcings, which are felt by the surface DGVM and fed-back to the climate. Higher-resolution processes such as deforestation, land use management and associated (as well as natural) fires are resolved at the local level. Anthropogenic LUCC (such as deforestation and pasture burning) is modeled using Geographical Information Systems (GIS) and spatially-explicit models. Modifications to the land surface are imposed on the land model, which has a potential feedback on the land surface properties through processes resolved by the atmospheric and land models. Fire behavior is modeled at the regional scale (~100m) to represent the detailed landscape using semi-empirical or empirical fire spread models. Improved parametrizations from our fully-coupled experiments, for use in atmospheric and land surface models, will allow for a better understanding and evaluation of CO2 emissions from LUCC and feed-backs with climate change.

Severe hydrological droughts in the Amazon have generally been associated to strong El Niño events. More than 100 years of stage record at the port of Manaus confirm that minimum water levels generally coincide with intense warming in the tropical Pacific sea waters. During 2005, however, the Amazon experienced a severe drought with great ecological and social impact, and who was not associated to an El Niño event. Unless what usually occur during strong El Niño events, when negative rainfall anomalies usually affect central and eastern Amazon drainage basin; rainfall deficiencies in the drought of 2005 were spatially constrained to the west and southwest of the basin. In spite of this, discharge stations at the main stem recorded minimum water levels as low as those observed during the basin-wide 1996-97 El Niño related drought. Besides this, stage data and satellite images indicate that floodplain lakes surface areas were more reduced during the recent drought. This paper examines why river discharges were so low during the 2005, even though rainfall deficits were restricted to a fraction of the whole basin, and why the impacts on the main stem floodplain were so severe. The analysis of river discharges along the main stem and major tributaries during the drought of 2005 revealed that the recession on major tributaries began almost simultaneously. This was not the case in the 1996-97 drought, when above normal contribution of some tributaries for a short period during high water were crucial to partially counter balance high discharge deficits of the other tributaries. Since time-lagged contributions of major tributaries are fundamental to damp the extremes in the main stem, an almost coincident recession in almost all tributaries caused a rapid decreased of water discharges during the 2005 event. Perhaps one of the most important lessons to be learnt from the drought of 2005 is that, from a hydrological point of view, more importantly than the size of the area affected by negative rainfall anomalies is the timing and location where those rainfall deficits occur. In conclusion, localized drought might have a greater impact on main stem river discharges providing rainfall deficiencies produces a simultaneous recession of major tributaries.