| Grant number: | 07/07834-3 |
| Support Opportunities: | Regular Research Grants |
| Start date: | April 01, 2008 |
| End date: | March 31, 2010 |
| Field of knowledge: | Physical Sciences and Mathematics - Geosciences - Physical Geography |
| Principal Investigator: | Maria Elisa Siqueira Silva |
| Grantee: | Maria Elisa Siqueira Silva |
| Host Institution: | Faculdade de Filosofia, Letras e Ciências Humanas (FFLCH). Universidade de São Paulo (USP). São Paulo , SP, Brazil |
Abstract
Climatic and vegetation coverage conditions define mostly the use of land made by man throughout time. In general, agricultural and pasture land uses are related to the restriction imposed by atmosphere and soil conditions. The identification of areas with potential to aridity due to climatic conditions contributes to definition of the surface vulnerability. Atmosphere and biosphere are mainly linked through heat, vapor and trace gases exchanges. Strong dependence on climatic (temperature, humidity and precipitation) and soil (soil wetness and land uses) conditions is establisled in the dynamic of these relations. Many studies point out changes observed in precipitation patterns as a result from surface vegetation modification or, more specifically, of changes in heat and vapor exchange, which can be due to albedo, soil wetness, surface rugosity and ecofiosiology differences. Climatic conditions over Amazonian region may, as stated by many authors, be conditioned by large scale deforestation, providing decrease in precipitation and increase in air temperature near surface. In these cases, reduction in precipitation is due to the air convergence and latent flux weakness at lower troposphere levels; the temperature elevation is related to the increased sensible flux provided by the energy balance described in the models. Important biophysical factors, in case of replacement of tropical forest by grassland type, that directly influence the water vapor flux reduction from surface are vegetation rugosity and root length reduction, leading to less precipitation. On the other hand, studies on regional scale reveal an increase in precipitation over deforested areas as a result of secondary circulation. Although the results from climatic simulation considering variations in chemistry atmosphere composition have pointed out in the last years a great probability of changes in regional climatic patterns (IPCC, 2007), also point out an uncertainty level due to the employment of different and not accurate enough parameterizations and relatively low spatial resolutions, leading to different simulated results. The uncertainty level in simulations and not thoroughly comprehensible relationships existent between biosphere and atmosphere impose a general need in expending more efforts on studies related to climatic impact. The low climatic predictability observed at the central portion of South America (at subtropical latitudes), the increasingly replacement of its natural vegetation coverage by cropland and pasture and its densely populous condition are other three aspects reinforcing the need of attention that must be directed to this region. Regional atmospheric models coupled to biosphere schemes present a sufficient complex portrait to represent relationships between biosphere and atmosphere. The global geographic variations on vegetation due to climatic conditions have been verified with the aid of biogeographic models or potential vegetation models (Salazar et al., 2007). Such models consider as central paradigm the control exerted by climate on vegetation distribution. Salazar et al. (2007) used a potential vegetation model in order to estimate the vegetation geographic distributions based on climatic scenarios of CO2 emissions, from 15 Coupled Ocean-Atmosphere GCMs for the IPCC AR4. All climatic scenarios used in Salazar et al. (2007) led to the strengthening of aridity conditions with distinct intensities, mainly over the central portion of South America and the eastern part of Amazonian region. The goal of this research is to verify the climatic impact due to surface changes during specific climatic conditions on the central portion of South America. The changes in vegetation type and area will be considered as those obtained by Salazar et al. (2007). The regional model RegCM3 coupled to Biosphere-Atmosphere-Transfer-Scheme (BATS) will be used to run the simulations. (AU)
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