Método para análise da relação entre florestas e vazões em bacias hidrográficas

Abstract

Studies of river basin flows are extremely important. However, the relation between forest cover and water flows is complex and still controversial in the scientific environment. In this context, this work was proposed aiming to analyze the water flows of 25 sub-basins of Espírito Santo, investigating their relation with the percentage of existing forest cover. Annual precipitation data provided by Xavier, King e Scalon (2016) were used for the hydrological year 2007/2008. The annual data of specific average water flow (qmed.) and average minimum specific water flow in seven consecutive days (q7) were obtained from fluviometric stations, together with ANA. In the delimitation of the sub-basins, the MDE SRTM was used, with spatial resolution of 30 meters. The forest cover data were obtained from the aerophotogrammetric survey conducted by IEMA between 2007 and 2008. Analysis of simple linear regression, multiple regression and partial correlation between the percentage of forest cover, precipitation and flows were performed, using data from all sub-basins. The analysis of hierarchical grouping was also applied, in order to group the sub-basins by precipitation, area and precipitation characteristics and area. Significant associations were found between the forest and the water flows only in the groupings of sub-basins made by precipitated annual total and by precipitated annual total associated to the area of the sub-basins. It was verified that the forest showed a relation with negative tendency when associated, to a significant extent, with q7. Likewise, for rainfall grouping, there was a negative association with forest cover. At the same time, it was identified that the forest positively influenced the qmed in the cluster formed by precipitation and area. The results show that the clusters performed were determinant to obtain distinct answers and significance detection, especially regarding the relation between the forest cover and the water flows. Moreover, they indicate that in most cases no significant relationship was observed between forest and water flow. However, it is possible that some associations have not been detected by the methods used. In this sense, it is demonstrated the need to x develop new studies, in scale of basins or groups of hydrographic basins, increasing new environmental variables, in order to obtain more detailed answers of the hydrological behavior of the basins of the state of Espírito Santo, assuming the complex relation between forest cover and its impacts on the water flows.