Hierarchical Calibration of SWAT model for a watershed in southern Brazil

One of the main challenges of hydrological modeling is the effective calibration of model parameters. The aim of this study was to test a hierarchical calibration scheme for the Soil and Water Assessment Tool (SWAT) model by considering land use and climate changes. The study area was the Rio Negrinho watershed, located in Santa Catarina State, Brazil. Model calibration was performed with the Sequential Uncertainty Fitting (SUFI2) Algorithm through increasing complexity tests. The observed discharge data were first divided into calibration and validation periods(Split Sample Test) wherein the predicted monthly flow matched the measured values, with a Nash-Sutcliffe coefficient (NSE) >= 0.5 and Pbias<+/- 25%. When wet and dry periods were considered separately (Differential Split-Sample Test) the NSE values of wet years (2008 a 2012) were higher than dry year values (2003 to 2007). In the SWAT validation for a watershed with similar land use (Proxy-Catchment Test), the model could not capture the flow peaks well (NSE of 0.0), however, the water balance volumes were compensated (Pbias of 0.1%). The case study demonstrates that SWAT performance varies greatly, depending on the spatial scale and calibration period. The SWAT model can be used in further studies to simulate land use and climate change scenarios however it must be calibrated and validated using spatially well distributed data and recorded series segment including dry and wet periods.