Impacts of the agricultural expansion in the Brazilian legal Amazon on the surface runoff generation: A study case

Abstract

Land use and land cover changes have as consequence several social, economic and environmental impacts. The objective of this work was to perform an analysis of the land use and land cover changes of a region in the Brazilian Legal Amazon, and to evaluate its impacts in the surface runoff generation. This study case took place at the Suiá-Miçu river basin, located at the northeast region of the Mato Grosso State. Three dates were chosen in order to perform this study: 1973, 1984 and 2005. The Automated Geospatial Watershed Assessment Tool (AGWA) was used in order to perform the surface runoff modelling. The results showed that until 1984, 13% of the natural vegetation of the drainage basin had been replaced by pasture. These changes were responsible for a 5.7% increase in the surface runoff annual average of the basin when compared with the equivalent values of 1973. However, in some regions the runoff increase reached 24%. In 2005, the agricultural areas increased to around 40% of the drainage basin, being 28% occupied by pasture and 12% by crop fields. The model showed for this scenario that the surface runoff annual average was 37% higher than in 1973 for this drainage basin, and that in some crop areas it was up to 160%.