SILVA, R. M. P.; http://lattes.cnpq.br/4219365262955692; SILVA, Rosângela Maria Pereira.
Résumé:
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.
