Alteração da cobertura vegetal na sub-bacia do Rio Espinharas no Período 2000-2010: o geoprocessamento como ferramenta para o gerenciamento ambiental.

Abstract

The vegetation is one of the most important components of biota playing a key role in the conservation of quantity and quality of water resources. In the context of the semiarid region of Paraiba and Rio Grande do Norte, the increase in the deforested area and the non-recovery of caatinga areas already degraded in the sub-basin area of Espinharas river, weaken increasingly its soils and hydrological balance. This work aimed to map the alteration in vegetation cover in the sub-basin area of the Espinharas river in the period 2000-2010, with the use of remote sensing techniques applied to geoprocessing. The hydrogeographic characterization of the area allowed an interrelated view of the different elements that define its weather and soil conditions, major conditions for vegetation. The image data from the orbital sensor TM - Thematic Mapper - from the satellite LANDSAT -5 were processed in the computing environment through the Georeferenced Information Processing System SPRING. For evaluation of vegetation cover of the studied area was used the Normalized Difference Vegetation Index - NDVI, widely used in evaluating the effect of vegetation cover and cited in the literature as suitable for the semiarid regions. In 65% of the area low values predominated, between 0 and 0,1, characteristic of areas with high anthropogenic, sparse vegetation and exposed soils. To classify the plant formations of the area, the following classifications were adopted: open arboreal-shrubby caatinga (T2), closed arboreal-shrubby caatinga (T3), and closed arboreal caatinga (T4) in the visual analysis of the variables tone / color and texture in the adjusted multispectral composition. The subtraction between 2010 and 2000 NDVI images generated the difference image, whose values were analyzed taking into account the values of the average distribution of gray levels in the image (u) standard deviation (s) according to the thresholds [0, u - s ], [u - s, u + s ] e [u + s, 254], related to the classifications: deforestation / reduction of vegetation cover, no change and areas of regeneration / growth of vegetation. The results showed that 80% of the area remained unchanged in the period. An impoverished caatinga in herbaceous, shrub and tree species, long subjected to mankind's action and to different agents of erosion. A reduction of vegetation cover occurred in 12,6% of the area, due to the permanence of the practice of clear cutting of vegetation for stem production, coal, obtainance of firewood for domestic or commercial use and area preparation for agriculture. There was an increment in 7,4% of the area possibly favored by the cultivation of irrigated and non irrigated pastures in alluvial soils, as the waters of the reservoirs were retreating. The use of satellite images and application of geoprocessing to collection, systematization and analysis of data regarding the conditions of the natural elements, proved to be essential for the development of the research, and useful to support interventive actions of society and public bodies in the process of recovery and preservation of natural resources especially in the semiarid region.