The influence of the vegetation cover on the shallow geothermal system was observed in the sites studied. There were variations of monthly average values of temperature between the places with and without vegetation cover. During the "dry" period, this variation was up to 6.01 • C at the depth of 0.02 m, and 2.84 • C at the depth of 1.0 m. During the "rainy" period, however, the variation was up to 2. Palavras-chave: geotermia rasa, temperatura, cobertura vegetal, condutividade térmica, fluxo geotermal raso.
Estimates have been made of ground surface temperature (GST) variations for 25 localities in the region of Manaus (province of Amazon in Brazil) making use of both forward and inverse models. The work is based on analysis of borehole temperature logs as well as remote sensing data concerning changes in vegetation cover. Results of functional space inversion (FSI) of borehole temperature data reveal the occurrence of a cooling event, with a decrease in temperature of slightly less than 1oC, for the period of 1600 to 1850 AD. This episode coincides roughly with the period of “little ice age” in the southern hemisphere. It was followed by a warming event, with magnitudes varying from 2 to 3oC, that lasted until recent times. Integration of these results with estimates based on changes in normalized index of vegetation cover (NVDI) of the last decade points to continuation of climate warming over the last decade. This event is found to be prominent in areas of deforestation in central parts of the Amazon region.
Results of recent measurements of methane in stable interior parts of Brazil, where subsurface strata have very little organic matter, are found to be compatible with the hypothesis of its deep crustal origin. Analysis of observational data indicates that seepage through submerged fault systems contribute to methane flux in hydroelectric reservoirs. The main conclusion is that hydroelectric reservoirs impede, rather than promote, natural flow of methane of mantle origin. Consequently, supposed impacts of global warming by methane flux in hydroelectric reservoirs are unfounded.
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