Comparação entre NDVI e SAVI na determinação da perda de solo na bacia hidrográfica Piancó-Piranhas-Açu

Abstract

Soil loss due to water erosion is one of the main mechanisms of soil degradation worldwide, and the search for alternatives to monitor this problem becomes essential for its control. The present study aims to compare the NDVI and SAVI indices as an alternative way to determine the cover and management factor of the Universal Soil Loss Equation in order to quantify soil loss in a semi-arid watershed. Initially, bands 4 and 5 of the Landsat-8 satellite were collected for a pre-established period according to the climatic seasonality of the semi-arid region, which were used to create the vegetation indices and later applied to the calculation of the cover and management factor. To determine the other factors of the Universal Soil Loss Equation, data from studies in similar areas and from governmental water resources management agencies were compiled. All data were processed in QGIS software, where soil loss modeling was generated for both scenarios using map algebra. In both cases, very similar values were found for the cover and management factor, ranging from 0.0440 to 0.7126 when calculated using SAVI and from 0.0446 to 0.7088 using NDVI. Consequently, similar annual average soil loss values were also observed, with the Orthic Natric Planosol being the most susceptible soil class in both scenarios, presenting values of 6.618 t·ha⁻¹·yr⁻¹ for the SAVI model and 6.519 t·ha⁻¹·yr⁻¹ for NDVI. The lowest values were associated with dystrophic Yellow Latosols, with 1.225 t·ha⁻¹·yr⁻¹ and 1.199 t·ha⁻¹·yr⁻¹, respectively. Despite NDVI limitations in temporal analyses in semi-arid environments, both indices demonstrated similar effectiveness in watershed-scale soil loss modeling in a semi-arid context, proving to be viable alternatives for determining the cover and management factor in the absence of empirical data.