Análise das fragilidades ambientais na sub-bacia hidrográfica do Riacho do Sangue, Ceará

Abstract

The watershed, as a water resources management unit, originated in the observation that aquatic ecosystems are essentially open systems, exchange matter and energy with each other and with adjacent terrestrial ecosystems. Therefore, the analysis of this type of system provides the integration of knowledge about its elements, structures and functions in a way that facilitates the implementation of measures that can ease the environmental problems faced. In semi-arid regions, such as in the case of the Brazilian Northeast, these problems are exacerbated by the vulnerability of the environment, where water resources, soil and vegetation are severely degraded, increasing their susceptibility. Thus, the present study aims to analyze the environmental fragility, under the integrated perspective of the landscape, caused by the natural conditions added to the contribution of the anthropic actions of land use and occupation in the watershed of Riacho do Sangue, a tributary of the Castanhão reservoir, semi-arid region of Ceará. For this purpose, the methodological proposal of Ross (1994) is added to the use of GIS and Remote Sensing, where it was possible to integrate the various environmental components. The results were characterized as charts of potential and emerging fragility, with levels varying from very low to high, obtained through the use of geotechnologies associated to map algebra. When analyzing only the natural attributes, it was observed that 81% of the sub-basin area comprises the mean potential fragility class, while the low potential fragility class occupies approximately 11% of the area. The high potential fragility class had the lowest representativeness, only 8%. When inserting the use and occupation of the soil in the calculation of emergent fragility, it was obtained that 60% of the area comprises the middle class fragility emergent, with 33% being in the class of low fragility. It was verified that in the places where there are bigger patches of preserved forest, the fragility levels, previously identified in the mapping of the potential fragility, are attenuated, emphasizing the importance of the vegetation for the maintenance of the environmental quality. Through these documents it becomes possible to point out the areas where the degrees of fragility are lower favoring, then, certain types of insertion; and more fragile areas where more technically appropriate actions are needed.