Evolução do uso e cobertura na Bacia do rio São Francisco e seus impactos nas variáveis hidrológicas.

Abstract

The growing impact of human activities on the environment has increased their influence on the planet's natural cycles. As for the hydrological cycle, these activities started to impact it in a more representative way, influencing the availability of water and surface water flows. In a watershed, these activities impact its hydrological cycle, modifying fundamental processes for the watershed's water and energy balances. In this context, the present work sought to evaluate the impacts of anthropogenic modifications on the hydrological cycle of the São Francisco River Basin (SFRB) between 1985 and 2015. The study area comprised the entire SFRB, for a more general analysis, and 10 sub-basins that comprise it, for more specific analyses. The data used covered Land Use and Land Cover (LULC) data and precipitation, flow, and temperature data. The methodology incorporated: i) the assessment of LULC dynamics; ii) the trend analysis with the Mann-Kendall method and slope Sen; iii) the decomposition of the total streamflow variation with Budyko's hypothesis and with the concept of climatic elasticity of streamflow and iv) hydrological modeling with the Soil Moisture Accounting Procedure (SMAP) model, using the DiffeRential Evolution Adaptive Metropolis (DREAM) method for model calibration under parametric uncertainty. With this, it is possible to detect a clear anthropic modification of the SFRB, led by the expansion of agriculture and cattle ranching. Trend analysis exhibited positive trends for potential evapotranspiration throughout the basin, negative trends for streamflow rates, and generally no trend for the precipitation series. The decomposition of the total variation in streamflow, in both approaches used, pointed to a greater contribution of the anthropic component in most of the sub-basins evaluated. The coefficients of climatic elasticity of streamflow pointed to an increased sensitivity to climate variations in the period considered. The evolution of the frequency distribution of SMAP parameters over the evaluated period indicated changes in several processes of the hydrological cycle, such as: decrease in aquifer recharge, decrease in baseflow, increase in runoff generation and reduction in infiltration. The results allowed to identify and quantify the impacts of anthropic modifications on the hydrological cycle of the SFRB.