Avaliação de áreas afetadas por queimadas e incêndios florestais no estado do Tocantins em 2015

Abstract

The remote sensing techniques can be used for the detection, monitoring or identification of burned areas, as well for the analysis of the characterization and evaluation of occurrences of phenomena in a landscape at different temporal / spatial scales. The present study aims to analyse burned areas in the 2015 season, in the basins and sub-basins of the Araguaia-Tocantins hydrographic systems in the state of Tocantins. The quantification and delimitation of burned areas were carried out using two RGB compositions (754; 653) derived from Landsat8 satellite images and dry season. In addition to the variables related to a characterization of the burned area in each of the 30 hydrographic systems in the state of Tocantins, landscape metrics, number of hotspots and the results of the spatial autocorrelation were used too in analysis of correlation and principal components. The burned area had shown a positive correlation with the following variables: area occupied by the system (0.72 **; 0.87**) and the percentage of burned area (0.78**; 0.86 **). However, negative values were observed with the percentage of the burned area within the agricultural areas (-0.55 **; -0.80**). The correlation analysis also showed the relation of the burned area with the number of hotspots (0.75 **; 0.90**) and number of hotspots within the burned areas (0.95**; 0.97**). With smaller magnitudes, significant correlations were observed with the number of days without rain (0.51**; 0.63**) and number of days with rain less 13 mm (0.55 **; 0.81**). About the principal components analysis, it was possible to extract four components with first detail 44.05% of the variance, the second 16.69%, the third, 12.67% the fourth 9.66%, which they were represent the 83.03% of the variance of the original dataset variability. In nine sub-basins of the state were observed burned areas above 100 thousand hectares in 2015: A2 (> 501,000 ha); T1 (> 406,000 ha); T10 (> 248,000 ha); A1 (> 199,000 ha); A3 (> 176,000 ha); T12 (> 126,000 ha); T9 (> 117,000 ha); T5 (> 113,000 ha); T14 (> 101,000 ha), which they were represent more than 77% of the mapped in the state. The landscape metrics had shown the small relationships with burned area, however, in the system with the second largest occurrence of the burned area was observed relationship with the fragmentation of the landscape. The systems with the highest occurrence of burned areas can be characterized by regular or more complex landscapes, as well as the grouped occurrence of fire.