Analysis of seasonal environmental fragility using the normalized difference vegetation index (NDVI) and soil loss estimation in the Urutu watershed, Brazil.

Abstract

Land use intensification has contributed to the emergence of impacts on the environment such as soil loss, silting of watercourses, and biodiversity reduction, among others. Using models that can seasonally diagnose environmental damage is of fundamental importance in territorial planning and management. This work aimed to analyze the seasonal Environmental Fragility (EF) from the autumn of 2019 to the summer of 2020 using the soil loss estimate. To do this, data such as slope, erodibility, erosivity and the normalized difference vegetation index (NDVI) were used. Statistical tests were also applied to assess the significance level of the models in the seasonal evaluation, as well as in the validation based on ground truth points. The results showed that there is seasonal differentiation in the EF and in the soil loss estimation, in which NDVI and erosivity are two of the main responsible factors. Spring was the one that resulted in the largest area classified as high EF (27%) and with an estimated soil loss of 0.3733 t.ha-1month-3. The summer presented the highest soil loss estimation with an average value of 0.4393 t.ha-1month-3. Autumn (0.07683 t.ha-1month-3) and winter (0.0569 t.ha-1month-3) showed the lowest rates of soil loss and the largest areas classified in the low class of EF, as a result, mainly, of the erosivity of the rains. The results indicated by the seasonal models of EF and soil loss were validated through erosion points using spatial statistics tests.