Levantamento do meio físico do município de Araxá-MG, utilizando técnicas de geoprocessamento

Abstract

The twofold aim of this work was to survey the physical environment of the municipal district of Araxá MG, using geoprocessing techniques, and to evaluate the evolution occurred in land use in two different periods: 1985 and 2005. Araxá is located in the Alto Paranaíba Macrorregion in Minas Gerais State, between the geographic co-ordinates 19º25 53 - 19°50 09 South latitude and Greenwich 46°44 27 - 47°13 38 West longitude. With an area of 1,166.96km2 and 367km from the capital of Minas Gerais, the city had a population of 78,997 inhabitants in 2000. In order to carry out this work, topographic charts, geomorphologic mapping and 1985 TM/Landsat 5 and 2005 CCD/CBERS satellite images were used. The survey of the physical environment was carried out based on the themes of contour, drainage and the district boundaries that made it possible to prepare the thematic maps of the watersheds, slopes, hypsometry, geomorphology and land use (1985 and 2005). The thematic maps were elaborated using the IDRISI software, which also allowed evaluation of the areas, as well as the cross tabulation between the different thematic maps. From the data analysis, one can verify that the district comprises 10 watersheds of which Ribeirão do Inferno and Marmelo Watersheds are the larger, taking up approximately 42% the municipal area. Slopes greater than 8%, those with relief varying from medially to strongly undulated, predominate the region. The degree of carving of the valley walls varies from weak to strong and drainage density varies from medium to low. Altitudes between 900 and 1200m predominate. The data originated from the maps and tables allowed comparison and analysis of the evolution of land use in the two periods and evaluation of the adequacy of land use according to the physical environment. Ten categories of land use (Pivot, Urban and Mixed Use, Rupestrian Field, Reforestation, Water Bodies, Farming, Mining, Forestry, Pasture and Savanna) were identified and mapped. In 2005, 46.22% of the area of the district was occupied by Pasture, followed by Rupestrian Fields (14.34%), Farming (16.12%) and Forest (15.49%). The other categories presented almost insignificant percentages. Within this twenty-year period, Pasture area was reduced while Farming, Urban and Mixed Use, Reforestation and Mining areas increased. A reclassification was made for the final analyses of land use in Araxá, so that only two categories remained: natural vegetation and anthropic activities. It was concluded that in terrains with high slopes, the larger areas are occupied by natural vegetation, while in terrains with low slopes, anthropic activities occupied the largest area. As for hypsometry, it is verified that in more elevated altitudes the natural vegetation (Rupestrian Field) predominates, and in lower altitudes anthropic activities predominate. The Ribeirão Marmelo Watershed is responsible for 48% of the farming area in the district; 68% of the Rupestrian Fields are located in the Ribeirão do Inferno Watershed; 98% of Mining areas are located in the Córrego do Sal, Ribeirão Capivara and Ribeirão Pirapetinga watersheds; 44% of the remaining Savanna is in the Córrego da Galinha Watershed; 42% of Forested area is located in the Ribeirão Capivara and Córrego Fundo watersheds. Geoprocessing has demonstrated itself as the best technique for achieving more accurate and reliable results. The interpretation of satellite images in different periods associated with other kinds of data (maps, laboratories and field) when integrated in a GIS, permits analysis and evaluation of the geographic space, providing important information to the municipal administrators.