Aplicação do índice de vegetação por diferença normalizada (NVDI) associada às variáveis pluviométricas para sub-bacia do Rio Espinharas, PB/RN.I

Abstract

In order to development the means of conservation and maintenance of water resources it is necessary to understand the interactions between rainfall and the dynamics of vegetation in space/time, which has been possible due to the use of NDVI. The sub-basin of the Espinharas River undergoes great changes in its landscape, mainly caused by the expansion of anthropic activities, therefore, it is expected to demonstrate the relationship between the NDVI and the precipitation in the mentioned sub-basin. The aim of this paper was to verify the behavior of the Normalized Difference Vegetation Index (NDVI) at the sub-basin of the Espinharas River in the dry and rainy periods between 2005 and 2015, correlating it with accumulated precipitation in each period. A dot mesh representing the geographical location of 12 data collection platforms (DCP) was generated. From each DCP, a 5 km radius was determined, in which 30 sampling points were randomly selected for acquisition of NDVI rates in areas of natural vegetation. Considering the variation of the NDVI in the study area during the analyzed period, it is possible to observe significant changes in the concentration of caatinga vegetation from the rainy period to the dry period. The year 2005 presented the highest values of NDVI in relation to 2015, with the highest amounts of 0.71 and 0.78 in the dry and wet periods, respectively. In 2015, the maximum values were 0.64 and 0.61 for the dry and humid periods, respectively. The highest values were observed in the rainy season of 2005, in the meteorological stations of Maturéia, Salgadinho and Areia de Baraúnas. These areas are marked by the presence of dense native vegetation found in the highest areas of the land area, such as hillsides. Regarding the dry period, low variations in the NDVI rates were observed, with the highest readings observed in the platforms of Maturéia, Salgadinho and Teixeira, in the years studied. The platforms that presented the greatest reductions in NDVI values from one year to another in the rainy season were Maturéia, Santa Teresinha and Salgadinho, with reductions of 41.9%, 38.2% and 32.7% respectively. The most significant correlations for the analyzed variables were established for the dry periods, with Pearson correlation coefficients of 0.71 in 2005 and 0.48 for 2015. Such findings indicate a progressive connection between the variables with the decrease of rainfall totals. The lowest correlations were observed in the rainy season, with rates of 0.09 in 2005 and 0.19 in 2015. The increase in rainfall levels in the region did not imply a progressive increase in NDVI values. It is suggested that, for new studies in the region, a longer period of observation over the years should be explored in order to minimize the effect of extreme situations. In addition to the accumulated rainfall, other factors could be related, such as the steepness of the land area, temperature and soil type, which are important factors to be considered, suggesting a combined analysis among them.