Caracterização espaço-temporal das alterações ambientais decorrentes da construção da usina hidrelétrica de xingó no município de Piranhas – AL

Abstract

Actually, the hydroeletric plants are the principal electric power source in Brazil, their installation generate several socio-environmental impacts at short and long term in large areas, being necessary to monitor constantily, principally when the plant is located in a bioma as caatinga that undergoes severe desforestment. In this context, the Xingó Hydroeletric Plant is presented, located between two counties: Canindé do São Francisco - SE and Piranhas - AL. Alagoas county has great historical importance besides being a great economic center in the past and with the plant implementation suffered several social and environmental impacts in your territory. This work has the purpose of using the remote sensing tools to analyze the spatio-temporal modifications caused by the Xingó Hydroeletric Plant in the Piranhas. For that, were selected orbital images from the satellites Landsat 5 and 8 from the years 1985, 1999, 2006 and 2020 and performed the supervised classification selecting 7 cateories for training the maximum-likelihood algorithm in order to get land use and cover data. Beyond the classification process, also were calculated the biophysicals indexes NDWI and NDVI. From the results were prepared the maps for land use and cover, and for NDWI and NDVI, obtained the quantitative and statistical data to analyze the results of each process. The supervised classification was realized using the software SPRING 5.5.6 and the indexes using the software QGIS 3.10. The NDWI and NDVI proved to be very effective to identify hydrous bodies and areas with vegetation as São Francisco River and the Caatinga Densa and Semidensa areas, the indexes results enable to observe the humidity of region and quality of vegetation present in Piranhas evindencing the arid weather in the region, besides, mostly of vegetation in the territory presents low humidity and hydrical stressed. Although to show confusion rate between few categories, the supervisioned classification results presented satisfactory performance what made to identify the hydrous bodies in the region, besides that possible the quantification of the selected categories and to observe the decrease and increase of a class over the time in the Piranhas territory, as an example the changes become in the área of Caatinga classes, as well the increase for Urban classe and the reducition in Non-vegetade area and farming area. Keywords: remote sensing; caatinga; supervisioned classification; NDWI; NDVI; Piranhas; Alagoas.