Publicações

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.

O modo como actuamos hoje relativamente às alterações climáticas acarreta consequências que perdurarão um século ou mais. Num futuro próximo, o resultado das emissões de gases com efeito de estufa não será reversível. Os gases retentores de calor emitidos em 2008 irão permanecer na atmosfera até 2108, e até para além disso. Por isso, as escolhas que actualmente fazemos não afectam apenas as nossas vidas, mas mais ainda as dos nossos filhos e netos. Isto faz das alterações climáticas um problema único, e mais difícil do que outros desafios políticos.