Simulação da vazão do Rio Tapajós utilizando modelo de swat com diferentes entradas pedológicas e climáticas

Abstract

Changes in aquatic ecosystems generated by agriculture, livestock, logging, mining and hydroelectric dams have provided the degradation of natural resources, as well as changes in water resources and river systems. Thus, prior knowledge on the effect of variations of land use regarding the dynamics of waters in river basins are important to predict, mitigate and/or eliminate activities and interventions with negative impacts The Tapajós River Basin, which is one of the main Amazon basins, has several activities that degrades the environment along its extension such as livestock farming, agriculture and logging. In this context, hydrological models are important tools to assess the impact that different farming practices and different uses and occupations cause in the soil erosion and their influence on the flow of the rivers due to the local climatic conditions. This work aimed to show if the SWAT model can efficiently predict the flow of the Tapajós river basin, evaluating different (pedological and climatic) input databases. In this way, we conducted a survey of climatic data involving climatic data such as precipitation, maximum and minimum temperature, average wind speed, relative humidity, as well as geocartographic data such as land use and occupation, soil type and numerical terrain model, which were used for the characterization and delimitation of the hydrographic basin. Three fluviometric points were used: Acará dos Tapajós (17650002), Fazenda Tratex (1730000) and Jardim do Ouro (17675000) with series between 01/01/1999 and 01/01/2002. Two different pedological inputs - Food and Agriculture Organization of the United Nations (FAO) and Empresa Brasileira de Pesquisa Agropecuária(EMBRAPA) - and two inputs of climatic parameters - Instituto Nacional de Meteorologia(INMET) and Global Precipitation Climatology Project (GPCP) - were used in this thesis to determine which one would give results closer to those that were observed. In the simulation without calibration, the fluvial stations Acará dos Tapajós (17650002), Itaituba (17730000) and Jardim do Ouro (17675000), all values were overestimated but they followed the same trend of observed values, providing unsatisfactory values for PBIAS (Percentage of BIAS) and COE (Nasch - Sutcliffe Efficiency Coefficient), demonstrating therefore the need of model calibration for better results. In the determination of the hydrological parameters, the ones that presented greater influence on modeling according to the global sensitivity analysis were those directly related to surface and underground flows: CN2, RCHRG_DP, GW_DELAY and CH_N2. Among them, CN2 presented greater sensitivity and importance for determining the direct flow volume of the Tapajós river flow, i.e., the number of the initial curve for the humidity condition II for almost all combinations of input data. After calibration, the simulation using INMET-EMBRAPA climatic data resulted in values of COE (0.81, 0.86 and 0.79) considered very good and superior when compared to the other results of the simulations using the other inputs. This shows that the model has a good correlation with the actual data and, therefore, represents the hydrological behavior of the Tapajós river basin.