Avaliação da fragilidade ambiental no setor de alto e médio curso da Bacia Hidrográfica do Rio São Lourenço - MT

Abstract

The São Lourenço River Basin is an important drainage system, with an area of over 24,000 km², almost all of which is within the Cerrados Morphoclimatic domain. The hydrographic network represents 10% of the Upper Paraguay Basin – BAP. The diversity of landscapes presents reliefs with a variety of shapes and structures, which result in a diverse surface and vegetative combination, with various types of uses. In its significant extension, several problems arise, such as erosion, soil loss, forest deforestation, and conflicts over water. Among the problems identified, deforestation stands out, where, according to MapBiomas (2022), 58.52% of the basin's coverage belongs to agricultural classes, while only 39.66% represents natural classes, a value close to the minimum limit of 35% preservation for the Cerrados Domain in the legal Amazon, according to law 12,651 (Brazil, 2012). In order to understand the study area in greater depth, the environmental fragility assessment is proposed as a way to understand physical vulnerabilities in interaction with socioeconomic actions, inspired by the methodology developed by Ross (1994). The methodology is subdivided into two stages: office activity and fieldwork. The first stage consists of obtaining geospatial data that will feed a geographic database and geoprocessing them. The second stage consists of photographic recording of samples in situ. The processed data are variables correlated in the fragility map, such as land use and cover, soils, relief dissection index and rainfall regime. Each variable has five classes, which represent fragility indices from 1 to 5, namely: ‘1 – Very Low’ and ‘5 – Very High’. Each variable had a particular weight assigned depending on the morphosculptural characteristic of each sector. The basin was fragmented into 1 km² cells, each cell had the indices of each variable added up, multiplied and had their arithmetic mean calculated. The results showed that through the methodology by weights it was possible to identify the importance of each variable in the definition of a class of fragility, in order to highlight which changes in the environment could exponentially increase natural fragility. In this sense, it was identified that the most frequent class of fragility is the 'Moderate' class, with 8,330 km², which has a representation of 37% of the entire high and medium course, of which 51% are composed of the Cerrado Stricto Sensu, this indicates that the possible conversion of these areas into agricultural uses should transform this entire area into classes of 'High' fragility, adding to the 18% already existing.