Abstract
One of the most effective procedures in the evaluation of degraded areas has been the use of remote sensing. The aim of this work was to evaluate the temporal dynamics of the NDVI and rainfall in detecting the degradation of natural resources in a semi-arid region of Brazil. The area under study is located to the west of the district of Taua, in the State of Ceara, with a predominance of shrub-like caatinga forest. Rainfall data was obtained from FUNCEME. Ten images (dry season) were acquired from a 27-year historical series (1985-2011) from the TM/LANDSAT5 sensor, later converted to surface reflectance using the FLAASH/ENVI extension; NDVI indices were obtained and divided into six classes corresponding to land usage and occupation. The mean values of the NDVI classes were submitted to statistical analysis and compared by T-test (p<0.05) and the Pearson correlation matrix. It was found that in the years with rainfall above the historical average (1985-1993 and 1996-2004) there was a significant increase in degraded areas, represented by low values for the NDVI (between 0 and 0.4), due to more land being used for subsistence farming. However, during periods of drought (1993-1996 and 2004-2011), the opposite behaviour was seen, characterised by the natural regeneration of the woody stratum due to agricultural areas being abandoned; behaviour that was evidenced by increases of up to 1,807% in the moderately high class of the NDVI (between 0.6 and 0.8). The spatial and temporal dynamics of the NDVI and the rainfall therefore played a part in detecting evidence of the process of degradation of the caatinga biome in an area of the district of Taua, in the State of Ceara.
Highlights
Tropical and subtropical forests occupy about 40% of the Earth’s surface and provide a habitat for more than 1 billion human beings (REYNOLDS; SMITH, 2002); among these are dry forests, which include the Caatinga and cover 42% (MOREIRA et al, 2006)
In view of the above, the aim of this work was to evaluate the temporal dynamics of the NDVI and rainfall in detecting evidence of the process of degradation of natural resources in an area of the district of Tauá, in the State of Ceará, Brazil
The NDVI values estimated for the western region of the district of Tauá were classified into six classes according to the protection offered the soil by the vegetation cover; these are: shadows and/or water sources (NDVI less than or equal to 0), bare soil and/or urban targets, very low (NDVI between 0 and 0.2), low (NDVI between 0.2 and 0.4), moderately low (NDVI between 0.4 and 0.6), moderately high (NDVI between 0.6 and 0.8) and high (NDVI between 0.8 and 1.0)
Summary
Tropical and subtropical forests occupy about 40% of the Earth’s surface and provide a habitat for more than 1 billion human beings (REYNOLDS; SMITH, 2002); among these are dry forests, which include the Caatinga and cover 42% (MOREIRA et al, 2006). The semiarid region of northeastern Brazil, where the dry forests stand out, comprises an area of approximately 982,563 km (BRAZIL, 2014; PEREIRA JÚNIOR, 2007). In this region, different vegetation typologies develop, with a predominance of caatinga, in an area of approximately 844,453 km, equal to 70% of the north-eastern region and 11% of the territory of the country (ARAÚJO; ALBUQUERQUE; CASTRO, 2007; BRASIL, 2014; RODAL; MARTINS; SAMPAIO, 2008). The Caatinga Biome presents floristic diversity, a result of varied phyto-ecological conditions. The natural landscape has almost lost its primary ecological characteristics due to the inappropriate use of socioeconomic activity. In the last few decades, the scenario has been greatly modified by intense anthropic action, mainly expressed by the emergence and/or intensification of such biophysical processes as soil erosion, increased water deficit, microclimatic change, a reduction in biodiversity and an increase in areas susceptible to desertification (TRIGUEIRO; OLIVEIRA; BEZERRA, 2009)
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