Análises fatorial e de componentes principais aplicadas ao estudo dos fatores influenciadores de processos erosivos
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Data
2020-02-03
Autores
Pascoto, Tamara Vieira
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Universidade Estadual Paulista (Unesp)
Resumo
A erosão é um problema ambiental em que a perda de solo pode acarretar problemas econômicos e, quando próximos a urbanizações, problemas sociais. A cidade de São Manuel está situada no interior de São Paulo e apresenta, tanto solos argilosos com baixa suscetibilidade a erosão, como solos arenosos com alta suscetibilidade a erosão. Uma vez que existem áreas suscetíveis à erosão próximas à área urbana capazes de colocar a população em risco, surgiu a necessidade de analisá-las a fim de auxiliar políticas públicas para minimizar suas consequências. Com isso, a presente pesquisa propôs o desenvolvimento de uma metodologia para gerar índices de erosão, por Análise de Componente Principal (PCA) e por Análise Fatorial, fundamentado em alguns dos principais fatores influenciadores nos processos erosivos que ocorrem na área urbana do município. Nessa etapa foram considerados: textura do solo; declividade; permeabilidade; uso e ocupação; pluviosidade; e erodibilidade dos solos. Inicialmente, foram levantadas as feições erosivas existentes na área urbana, espacializadas e classificadas. Entre as 9 feições espacializadas, duas eram provenientes de processos fluviais, duas estavam recuperadas, restando cinco feições erosivas lineares para serem estudadas. Uma das cinco, apesar de estar estabilizada, apresentou um avanço significativo em um dos braços. Das feições estudadas, apenas uma foi classificada como ravina, sendo as demais classificadas como voçorocas. Após levantados os fatores influenciadores, os mesmos foram avaliados segundo duas metodologias: Método A – baseou-se na análise de componentes principais, chegando-se em três índices distintos, um influenciado mais pela textura do solo, outro relacionado a declividade e outro a pluviosidade; e Método B - baseou-se em análise fatorial, chegando-se em um único índice, o qual se utilizou a porcentagem de argila, os dados de uso e ocupação e a declividade. Os índices foram espacializados em forma de mapas para auxiliar na análise concluindo-se que o método B foi mais eficiente para o estudo das erosões no município de São Manuel, por apresentar as melhores correlações entre os parâmetros e as feições. Além disso, esse método mostrou uma melhor facilidade na análise dos dados uma vez que ajustou os parâmetros em uma única equação.
Erosion is an environmental problem where soil loss can lead either to economic problems or, whether close to urbanization, social problems. São Manuel town is located in the interior of São Paulo and has both clayey soils with low susceptibility to erosion and sandy soils with high susceptibility to erosion. Since there are areas susceptible to erosion close to the urban area capable of putting the population at risk, the need arose to analyze them in order to assist public policies to minimize their consequences. Therefore, this research proposed the development of a methodology to generate erosion indexes, by Principal Component Analysis (PCA) and Factorial Analysis, based on some of the main factors influencing erosion processes that occur in the urban area of the municipality. At this stage the following factors were considered: soil texture; slope; permeability; use and occupation; rainfall; and soil erodibility. Initially, the erosive features existing in the urban area were surveyed, spatialized and classified. Among the 9 spatialized features, two were from fluvial processes, two were recovered, leaving five linear erosive features to be studied. One of the five, despite being stabilized, presented a significant advance in one of the arms. Of the studied features, only one was classified as ravine, the others being classified as gullies. After surveyed the influencing factors, they were evaluated according to two methodologies: Method A - it was based on the analysis of main components, arriving in three distinct indexes, one influenced more by the texture of the soil, another related to declivity and another to rainfall; and Method B - it was based on factor analysis, arriving in a single index, which used the percentage of clay, the data of use and occupation and the declivity. The indexes were spatialized in the form of maps to help in the analysis, concluding that Method B was more efficient for the study of erosions in the municipality of São Manuel, because it presented the best correlations between the parameters and the features. In addition, this method showed a better facility in the data analysis since it adjusted the parameters in a single equation.
Erosion is an environmental problem where soil loss can lead either to economic problems or, whether close to urbanization, social problems. São Manuel town is located in the interior of São Paulo and has both clayey soils with low susceptibility to erosion and sandy soils with high susceptibility to erosion. Since there are areas susceptible to erosion close to the urban area capable of putting the population at risk, the need arose to analyze them in order to assist public policies to minimize their consequences. Therefore, this research proposed the development of a methodology to generate erosion indexes, by Principal Component Analysis (PCA) and Factorial Analysis, based on some of the main factors influencing erosion processes that occur in the urban area of the municipality. At this stage the following factors were considered: soil texture; slope; permeability; use and occupation; rainfall; and soil erodibility. Initially, the erosive features existing in the urban area were surveyed, spatialized and classified. Among the 9 spatialized features, two were from fluvial processes, two were recovered, leaving five linear erosive features to be studied. One of the five, despite being stabilized, presented a significant advance in one of the arms. Of the studied features, only one was classified as ravine, the others being classified as gullies. After surveyed the influencing factors, they were evaluated according to two methodologies: Method A - it was based on the analysis of main components, arriving in three distinct indexes, one influenced more by the texture of the soil, another related to declivity and another to rainfall; and Method B - it was based on factor analysis, arriving in a single index, which used the percentage of clay, the data of use and occupation and the declivity. The indexes were spatialized in the form of maps to help in the analysis, concluding that Method B was more efficient for the study of erosions in the municipality of São Manuel, because it presented the best correlations between the parameters and the features. In addition, this method showed a better facility in the data analysis since it adjusted the parameters in a single equation.
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Palavras-chave
Erosão Linear, Índices de Erosão, Análise de componente principal, Análise fatorial, São Manuel, Erosion, Linear erosion, Erosion indexes, Principal component analysis, Factor Analysis