Land use and the hydro-sedimentological response of a watershed in a semiarid region. = Uso da terra e resposta hidrossedimentológica de microbacia no semiárido

In northeastern Brazil, with its semi-arid climate and an environment full of contrasts, side by side with the intensive exploitation of the natural resources by agricultural companies, it can be seen both agricultural and livestock farming being practised by small-holders as a way of earning their living. This exploitation is generally unsustainable, resulting in a scarcity of land and water resources, and having serious negative effects on this region. The objective of this research was to analyse the influence of anthropic action on the hydro-sedimentological responses of an experimental watershed with transitory drainage, located in the semiarid region of Ceará, during the years under study of 2009 and 2010: the catchment area of theobserved watershed being 2.8 ha. In 2009, the first year of the study, the native caatinga vegetation of the area was maintained unaltered; the following year a type of land use common to the region was applied, consisting of the removal of all vegetation followed by burning the land and cultivation of the grass Andropogon gayanus Kunt for the production of pasture. The rainy season of 2009 presented a total rainfall of 1,063 mm, 23.1% of the total precipitation being converted to surface runoff and resulting in a sediment yield of 730 kg ha-1. In 2010, due to the lower volume precipitated (809 mm), total runoff corresponded to 13.9%, but the sediment yield was maximized, with a total of 2,832 kg ha-1, this being 72% higher than in the previous year and demonstrating the negative effect of applied management. = Na regi o Nordeste do Brasil, com clima semiárido e ambiente de contrastes, verifica-se lado a lado a explora o intensiva dos recursos naturais por empresas agrícolas e a agricultura e pecuária praticada por pequenos produtores como forma de garantir a subsistência. Estas explora es ocorrem na grande maioria de forma insustentável, resultando na escassez dos recursos solo e água com sérios reflexos negativos nessa regi o. Objetivou-se com esta pesquisa analisar a influência da a o antrópica sobre as respostas hidrossedimentológicas em microbacia experimental de escoamento efêmero no semiárido cearense durante os anos de 2009 e 2010. A área de drenagem da microbacia estudada é de 2,8 ha. No primeiro ano de estudo (2009) a área foi mantida inalterada com vegeta o de caatinga nativa e no ano seguinte foi aplicado um tratamento de uso do solo comum na regi o, que consta de supress o da vegeta o, seguida de queimada e cultivo de gramínea Andropógon gayanus Kunt para a produ o de pastagem. A esta o chuvosa de 200