Spatial analysis of land use and land cover in the municipality of São Gabriel-Bahia, 2007 and 2018

Abstract

On a global scale, changes in land use and vegetation cover are happening very fast. In Brazil, the agricultural exploration process constitutes the greatest force of change in Land Use and Land Cover, a reality no different in the semi-arid region, where the municipality of São Gabriel is located, an area where this research was developed, characterized by intense use of resources natural. Therefore, the objective of the study was to analyze the changes in Land Use and Land Cover in the city of São Gabriel between 2007 and 2018. For that, some steps were developed, such as: construction of a database in a GIS environment, vector and raster data, georeferencing of tubular wells, Digital Image Processing (PDI), using TM/Landsat-5 and OLI/Landsat-8 satellite images, and supervised classification by region, generating maps of Land Use and Land Cover for the aforementioned period. Field work was carried out to validate the classification using the Global Accuracy method. The results show that the modernization of rainfed agriculture reached high productivity rates between the 1970s and 1980s, but on the other hand it increased the deforestation of the caatinga vegetation and increased the exposed soil with an advanced stage of degradation, causing a loss of productivity in this agricultural sector. Since then, irrigated crops have become frequent, which has led to an increase in the drilling of tubular wells, expanding the irrigated areas. The survey showed the changes that happened between 2007 and 2018: an increase of 1.65% in Irrigated Agriculture, and a reduction in Vegetal Coverage by -0.8%, and Agriculture-Exposed Soil by -1.1%. Water Bodies, Rocky Outcrop and Built-up Area increased their areas by 0.08, 0.1 and 0.25%, respectively. The fieldwork, combined with the analysis of the data generated from the classification of the images, it was possible to conclude that rainfed agriculture and pasture are still the main means of altering the caatinga vegetation in the study area, showing that this suppression of coverage over the years tends to contribute to the surface runoff of water and reduction of the soil infiltration capacity, increasing the erosion processes, mainly on the slopes of the Jacaré River valley and in the karstic plateau of the Baixão de Gabriel Sub-basin, causing siltation of drainage channels.