Análise do índice de vegetação por diferença normalizada (NDVI) da microrregião de Chapadinha-MA

Abstract

In recent years, agricultural expansion in Maranhão, driven by technological advances and the growing demand for commodities, has caused significant changes in the landscape, especially in regions within the MATOPIBA context. In this scenario, monitoring vegetation cover becomes essential to understand land use and land cover dynamics and their environmental impacts, since the suppression of native vegetation compromises essential ecosystem services, such as soil conservation and biodiversity. Remote sensing, through the analysis of electromagnetic radiation recorded by orbital sensors, stands out as an efficient tool for monitoring these changes at different spatial and temporal scales. In this context, the Normalized Difference Vegetation Index (NDVI) is an important indicator of vegetation vigor and the degree of anthropogenic interference in the landscape. This study analyzed NDVI dynamics in the Chapadinha microregion, Maranhão State, Brazil, from 2000 to 2020, aiming to evaluate vegetation cover evolution and land use and land cover changes. Images from Landsat 5 TM and Landsat 8 OLI/TIRS sensors were used, obtained through the Google Earth Engine platform and atmospherically corrected using MapBiomas data. Subsequently, the data were processed in QGIS 3.38.3 for territorial clipping, cartographic standardization, and quantification of land use and land cover classes. Statistical analyses included simple linear regression and Spearman’s correlation coefficient to identify temporal trends and relationships among the analyzed classes. The results revealed a significant reduction in natural formations, especially Savanna Formation, which showed a decrease of 39.1%, and Grassland Formation, with a reduction of 28%, while Forest Formation showed a smaller decline of 6.1% over the analyzed period. In contrast, anthropogenic classes expanded considerably, such as Urban Area (6,167.9%), Mosaic of Uses (66%), and Pasture (41.3%). A marked increase was also observed in the Beach, Dune, and Sandy Area class (29,317.7%) and in Wetlands (4,967.9%), indicating processes associated with environmental degradation and intensified human occupation. The reduction in NDVI values across large areas of the microregion reinforces the replacement of native vegetation by anthropogenic land uses, evidencing the pressure exerted by the agricultural frontier expansion in the MATOPIBA region. Therefore, NDVI proved to be an effective tool for identifying and quantifying land use and land cover changes in the Chapadinha microregion, contributing to the understanding of environmental impacts resulting from agricultural expansion and highlighting the importance of continuous monitoring and sustainable territorial planning.