Avaliação das alterações de vazões na bacia hidrográfica do rio São Francisco entre 1985 e 2019 : análise de tendências e relações com variáveis climáticas e antrópicas

Abstract

The effects of human interventions and climate change on the hydrology of watersheds have been widely discussed over the years. Flow studies are of great importance for the knowledge of water availability in a region. Indeed, understanding the combined effect of climate variables, water use and land cover is essential for the development of sustainable water resource plans. Based on this approach, the present work proposes to study the spatio-temporal behavior of the average annual flows in the São Francisco River basin (BHSF), in order to identify possible trends in the series and associate this behavior with climatic and anthropic variables. The basin in question was chosen because of the great variability of precipitation and diversity of land cover and use, with regions of intense agricultural activity and/or densely forested. First, the behavior of the average annual flow in three physiographic regions of the São Francisco River basin was evaluated. Subsequently, the behavior of climatic variables (rainfall, temperature, annual average evapotranspiration) and anthropic variables (water use, agriculture and natural vegetation) in three parts of the basin were analyzed. To analyze the behavior of these variables, three statistical tests were used (Mann-Kendall, Pettitt, Levene). In addition to hypothesis testing, wavelet spectral analysis was also used for climatic variables. Finally, to quantify and understand the combined effect of climatic and anthropic variables on the variability of flows, the Fu-type Budyko equation was used, together with the decomposition method. The results of the flow analysis showed signs of reduction in all the analyzed sections, however in the data of average annual precipitation it was not possible to verify a pattern of changes. In the temperature and evapotranspiration data, a change in behavior was observed with an increase in all regions. As for human activities, it was possible to identify a reduction in natural vegetation, an increase in agricultural areas and an increase in water consumption in all parts of the basin. Therefore, it can be seen that the analyzed precipitation does not seem to have an important influence on the changes in this flow, and the possible changes found in the flows may be related to temperature, evapotranspiration, agriculture, natural vegetation and water consumption. The results obtained from the application of the decomposition method show that climate change is the determining factor for the reduction of flow in the Upper São Francisco, in the Middle and Lower São Francisco human activities stand out.