Gestão dos recursos hídricos na bacia do rio das velhas: como podem os hidrológicos distribuídos subsidiar o planejamento?

Abstract

The management of water resources, particularly in anthropic areas is a great challenge given the inherent complexity of the different processes and spatial and temporal scales that occur. The hydrological modeling consists of a technique of representation of reality that allows a better understanding of the hydrological behavior of watersheds, as well as quantifying the positive and negative consequences of the changes in the land use (landscape dynamics) on the water yield. Among the models available for this purpose there is a Soil and Water Assessment Tool (SWAT) that is easily implemented in Geographic Information Systems (GIS). In this work, the SWAT was applied in the simulation of the hydrological processes of the Velhas River Basin, southeast Brazil, under different scenarios of land use. For modeling, tabular data (precipitation, solar radiation, wind speed, relative humidity and temperature) and spatial data (Digital Elevation Model, land use map, and soil type map) were required as inputs. The simulated water flow values were compared with the observed water flows obtained from the database of the National Water Agency (ANA). In the calibration of the model, the analysis period adopted was from 1995 to 2008, and validation was performed for the years 2009 to 2015. The simulation quality was evaluated through the Nash and Sutcliffe (NS), the percent bias (PBIAS), coefficient of determination (R²), and indexes extracted from the hydrographs (p-factor and r-factor). The results of the precision statistics were considered acceptable for all fifteen calibrated and validated sub-basins, indicating that the model was able to simulate properly the river flows. In this way, the model becomes suitable to evaluate the hydrological impacts caused by the changes in land use. The scenarios created were aimed at quantifying the effects of increased anthropogenic intervention in the basin to the detriment of forest areas, being: current use in the basin (C1), agricultural (C2) and urban (C3). In C2 and C3, the current area occupied by forests was replaced by agriculture and urban infrastructure, respectively. The time scale of the analysis comprises the years 1995 to 2015. In these new scenarios, there was an increase in surface runoff and a decrease in the base flow. The C3 scenario was the one with the greatest impact, the surface runoff was almost 3 times higher than in scenario C2, while the base flow was 52% lower. These results are important to support the actions of management of water resources by the National System of Management of Water Resources (SINGREH).