Marcos Heil Costa

Effects of large-scale changes in land cover on the discharge of the Tocantins River, Southeastern Amazonia

Studies that relate changes in land cover with changes in river discharge at the small scale ( 100 km2) usually have not found similar relationships. Here we analyse a 50-year long time series of discharge of a tropical river, the Tocantins River at Porto Nacional (175,360 km2), as well as precipitation over this drainage area, during a period where substantial changes in land cover occurred in the basin (1949–1998). Based on agricultural census data, we estimate that, in 1960, about 30% of the basin was used for agriculture. Previous work indicates that by 1995, agriculture had increased substantially, with about 49% of the basin land used as cropland and pastures. Initially, we compare one period with little changes in land cover (period 1-1949–1968) with another with more intense changes in land cover (period 2-1979–1998). Our analysis indicates that, while precipitation over the basin is not statistically different between period 1 and period 2 (α=0.05), annual mean discharge in period 2 is 24% greater than in period 1 (P<0.02), and the high-flow season discharge is greater by 28% (P<0.01). Further analyses present additional evidence that the change in vegetation cover altered the hydrological response of this region. As the pressure for changes in land cover in that region continue to increase, one can expect important further changes in the hydrological regime of the Tocantins River.

Combined Effects of Deforestation and Doubled Atmospheric CO2 Concentrations on the Climate of Amazonia

Abstract It is generally expected that the Amazon basin will experience at least two major environmental changes during the next few decades and centuries: 1) increasing areas of forest will be converted to pasture and cropland, and 2) concentrations of atmospheric CO2 will continue to rise. In this study, the authors use the National Center for Atmospheric Research GENESIS atmospheric general circulation model, coupled to the Integrated Biosphere Simulator, to determine the combined effects of large-scale deforestation and increased CO2 concentrations (including both physiological and radiative effects) on Amazonian climate. In these simulations, deforestation decreases basin-average precipitation by 0.73 mm day−1 over the basin, as a consequence of the general reduction in vertical motion above the deforested area (although there are some small regions with increased vertical motion). The overall effect of doubled CO2 concentrations in Amazonia is an increase in basin-average precipitation of 0.28 mm da...

Amazonia revealed: forest degradation and loss of ecosystem goods and services in the Amazon Basin

The Amazon Basin is one of the worlds most important bioregions, harboring a rich array of plant and animal species and offering a wealth of goods and services to society. For years, ecological science has shown how large-scale forest clearings cause declines in biodiversity and the availability of forest products. Yet some important changes in the rainforests, and in the ecosystem services they provide, have been underappreciated until recently. Emerging research indicates that land use in the Amazon goes far beyond clearing large areas of forest; selective logging and other canopy damage is much more pervasive than once believed. Deforestation causes collateral damage to the surrounding forests – through enhanced drying of the forest floor, increased frequency of fires, and lowered productivity. The loss of healthy forests can degrade key ecosystem services, such as carbon storage in biomass and soils, the regulation of water balance and river flow, the modulation of regional climate patterns, and the ...

Green surprise? How terrestrial ecosystems could affect earth’s climate

While the earths climate can affect the structure and functioning of terrestrial ecosystems, the process also works in reverse. As a result, changes in terrestrial ecosystems may influence climate through both biophysical and biogeochemical processes. This two-way link between the physical climate system and the biosphere is under increasing scrutiny. We review recent developments in the analysis of this interaction, focusing in particular on how alterations in the structure and functioning of terrestrial ecosystems, through either human land-use practices or global climate change, may affect the future of the earths climate.

Variação espacial e temporal da precipitação no estado do Pará.

Estudos sobre a climatologia das precipitacoes no Estado do Para sao essenciais para o planejamento das atividades agricolas. A variacao da precipitacao anual e sazonal no Estado do Para foi analisada com base em series historicas de 23 anos (1976-1998) de dados diarios de chuva. A analise foi realizada para 31 localidades do Estado do Para, sendo os resultados representados em mapas com a utilizacao de tecnicas de sistemas de informacoes geograficas (SIG). A variabilidade da precipitacao anual e sazonal foi caracterizada com base no coeficiente de variacao e no indice de variabilidade interanual relativo. A variacao desses coeficientes para a precipitacao anual no Estado do Para foi de 15 a 30%. As caracteristicas mensais da estacao chuvosa, em termos de inicio, fim e duracao, foram determinadas utilizando-se o criterio proposto por KASSAM (1979). A variacao entre as datas de plantio precoces e tardias corresponderam aos decendios identificados pelos dias julianos 309319 e 353363, respectivamente.

INCORPORATING DYNAMIC VEGETATION COVER WITHIN GLOBAL CLIMATE MODELS

Numerical models of Earths climate system must consider the atmosphere and terrestrial biosphere as a coupled system, with biogeophysical and biogeochemical processes occurring across a range of timescales. On short timescales (i.e., seconds to hours), the coupled system is dominated by the rapid biophysical and biogeochemical processes that exchange energy, water, carbon dioxide, and momentum between the atmosphere and the land surface. Intermediate-timescale (i.e., days to months) processes include changes in the store of soil moisture, changes in carbon allocation, and vegetation phenology (e.g., budburst, leaf-out, senescence, dormancy). On longer timescales (i.e., seasons, years, and decades), there can be fundamental changes in the vegetation structure itself (disturbance, land use, stand growth). In order to consider the full range of coupled atmosphere–biosphere processes, we must extend climate models to include intermediate and long-term ecological phenomena. This paper reviews early attempts a...

Confronting model predictions of carbon fluxes with measurements of Amazon forests subjected to experimental drought

Considerable uncertainty surrounds the fate of Amazon rainforests in response to climate change. Here, carbon (C) flux predictions of five terrestrial biosphere models (Community Land Model version 3.5 (CLM3.5), Ecosystem Demography model version 2.1 (ED2), Integrated BIosphere Simulator version 2.6.4 (IBIS), Joint UK Land Environment Simulator version 2.1 (JULES) and Simple Biosphere model version 3 (SiB3)) and a hydrodynamic terrestrial ecosystem model (the Soil-Plant-Atmosphere (SPA) model) were evaluated against measurements from two large-scale Amazon drought experiments. Model predictions agreed with the observed C fluxes in the control plots of both experiments, but poorly replicated the responses to the drought treatments. Most notably, with the exception of ED2, the models predicted negligible reductions in aboveground biomass in response to the drought treatments, which was in contrast to an observed c. 20% reduction at both sites. For ED2, the timing of the decline in aboveground biomass was accurate, but the magnitude was too high for one site and too low for the other. Three key findings indicate critical areas for future research and model development. First, the models predicted declines in autotrophic respiration under prolonged drought in contrast to measured increases at one of the sites. Secondly, models lacking a phenological response to drought introduced bias in the sensitivity of canopy productivity and respiration to drought. Thirdly, the phenomenological water-stress functions used by the terrestrial biosphere models to represent the effects of soil moisture on stomatal conductance yielded unrealistic diurnal and seasonal responses to drought.

Water balance of the Amazon Basin: Dependence on vegetation cover and canopy conductance

The availability and geographic distribution of fresh water resources may undergo significant changes in response to global environmental change. In this study, we examine the water balance of the Amazon Basin using a modified version of the LSX land surface model [Pollard and Thompson, 1995; Thompson and Pollard, 1995a, b] which includes a representation of land surface processes, canopy physiology (stomatal conductance, transpiration, and photosynthesis), and continental-scale hydrological routing. The model operates on a 0.5° by 0.5° grid and is forced with observed long-term climatological data. As an initial application of the model, we examine the seasonal variability of water balance within the Amazon Basin. The simulation is evaluated by comparing (1) simulated evapotranspiration with observations for different vegetation cover types and (2) simulated river discharge against the long-term records of 56 fluviometric stations spread throughout the basin. The model results show that evapotranspiration is strongly dependent on the vegetation cover, especially during the rainy season. Overall, we find good agreement between the simulated and the observed water balance: for most of the fluviometric stations the error is less than 25%. In addition, we perform a model sensitivity study to determine the role of changes in vegetation cover on the water balance, without considering feedbacks on climate. When forests, woodlands, and savannas are replaced with grasslands, annual average evapotranspiration decreases by ∼0.5 mm d−1 (∼12%), which is comparable to observations. Finally, we perform a model sensitivity study in order to assess the potential physiological effects of increased CO2 on stomatal (canopy) conductance and, as a consequence, on the water balance of the Amazon Basin, again without considering feedbacks on the atmosphere. The model results suggest that doubling atmospheric CO2 concentrations (from 325 to 650 ppmv) would decrease the canopy conductance by 20 to 35% (depending on the vegetation type) arid would decrease evapotranspiration by ∼4% throughout the region. As a consequence, annual river discharge increases by between 3% and 16.5%, depending on the position within the basin. At the mouth of the Amazon arid Tocantins Rivers, annual discharge increases by 5 and 9%, respectively.

MODIS land cover and LAI collection 4 product quality across nine sites in the western hemisphere

Global maps of land cover and leaf area index (LAI) derived from the Moderate Resolution Imaging Spectrometer (MODIS) reflectance data are an important resource in studies of global change, but errors in these must be characterized and well understood. Product validation requires careful scaling from ground and related measurements to a grain commensurate with MODIS products. We present an updated BigFoot project protocol for developing 25-m validation data layers over 49-km2 study areas. Results from comparisons of MODIS and BigFoot land cover and LAI products at nine contrasting sites are reported. In terms of proportional coverage, MODIS and BigFoot land cover were in close agreement at six sites. The largest differences were at low tree cover evergreen needleleaf sites and at an Arctic tundra site where the MODIS product overestimated woody cover proportions. At low leaf biomass sites there was reasonable agreement between MODIS and BigFoot LAI products, but there was not a particular MODIS LAI algorithm pathway that consistently compared most favorably. At high leaf biomass sites, MODIS LAI was generally overpredicted by a significant amount. For evergreen needleleaf sites, LAI seasonality was exaggerated by MODIS. Our results suggest incremental improvement from Collection 3 to Collection 4 MODIS products, with some remaining problems that need to be addressed

Trends in the hydrologic cycle of the Amazon Basin

Although previous studies have considered the long-term variability of precipitation and river discharge in the Amazon basin, other components of the hydrologic cycle, such as evapotranspiration and the transport of water vapor, have not received the same attention. This study examines the 20-year variability of the full hydrologic budget of the Amazon basin, using a 1976 -1996 time series from the National Centers for Environmental Protection/National Center for Atmospheric Research reanalyzed meteorological data set. Within this 20-year record, there is a statistically significant decreasing trend in the atmospheric transport of water vapor both into and out of the Amazon basin. This trend is associated with a general relaxation of the southeasterly trade winds, a weakening of the east-to-west pressure gradient, and a warming of the sea surface temperatures in the equatorial South Atlantic region. While the atmospheric transport of water vapor through the Amazon basin has decreased, the internal recycling of precipitation within the basin increased and basin-wide precipitation, evapotranspiration, and runoff have remained nearly constant. Even though basin-average precipitation and runoff have remained fairly stable, other components of the Amazon basins hydrologic cycle have been altered significantly by large-scale changes in atmospheric circulation.