Avaliação do nível de degradação das terras (desertificação) no alto curso da bacia hidrográfica do Rio Paraíba.

Abstract

Desertification is an environmental problem that affects several regions in the world, defined as the land degradation of arid, semi-arid and sub-humid areas resulting from various factors, including climatic variations and human activities. The aim of this study was to evaluate the level of land degradation (desertification) in the upper course of the watershed of Paraíba River, through the temporal and spatial dynamics of climatic, biophysical and socio-economic aspects. The upper reaches of the watershed encompasses all or part of the area of 18 municipalities, distributed among the micro-regions of Western and Eastern Cariri state of Paraiba. Period of climatic data were used in 1950 the 2013 for the variables: rainfall and aridity index (Ia), orbital data from sensors - MODIS (Moderate Resolution Imaging Spectro radiometer), from 2000 to 2013, to obtain the surface albedo and Vegetation Index adjusted to the ground (SA VI) and census data (population and agricultural) to quantify the socio economic index and the level of degradation in the region. The Mann-Kendall test (MK) was used to identify the time trend variable, the level of significance o f α = 0.05, the Sen method to quantify the trend and Kriging for analyzing spatial dynamics of the variables. The main results show that there is an increasing trend of rainfall and decrease dryness on the upper course of the watershed as a whole, during the period studied. You can infer that these conditions do not contribute to trigger land degradation process (desertification), suggesting that the causes of this environmental problem is not climate. The average annual precipitation increases in the north-northwest direction of the watershed, with minimum (320 mm) in Cabaceiras and maximum (680 mm) in Ouro Velho and Prata localities; the surface albedo and vegetation index have their values influenced by the seasonality of the region. Rainfall is the element that determines the increase in vegetation index and decrease in surface albedo, considering that these two variables have opposite behavior. The central region of the upper course of the watershed (municipalities of Congo, Camalaú and Caraúbas) showe d a low rate of vegetation and high albedo surface, possibly featuring a land degradation process. Throughout the period analyzed (2000-2013), these variables showed a downward trend, but not significant, showing a slight increase of land degradation. Rega rding the general socioeconomic index of each municipality – Isem it is observed that seven had "moderate" degradation ten "Low" degradation and only the municipality of Boqueirão presented situation of "Severe" land degradation. The municipality by Isem average values reveal what's going on land degradation across the upper course of the watershed, but in Moderate and Low levels, and northwest region of the area with increased human pressure. There is a tendency to increase the socioeconomic index - Iseb in the upper course of the watershed with an average value indicating the degradation of situation "moderate" land. This increase is the result of economic growth, implemented social programs and improvements in the living conditions of the population over the years.