A distributed model parameter optimization toolbox performing multisite calibration in the lump and distributed mode for the SWAT model

For watersheds with complex stream network or geographical heterogeneity, multisite calibration in the distributed mode is preferred for the SWAT model because parameters for sub-watersheds are calibrated independently. However, existing tools either can only perform calibration in the lump mode by calibrating parameters in identical ways across the whole watershed or perform sequential and cascading calibration. In this study, an open source toolbox named Distributed Model Parameter Optimization Toolbox for the SWAT model (DMPOTSWAT) is developed to perform multisite calibration in both the distributed and lump modes. Other functions including model evaluation with default parameter values, sensitivity analysis, selecting best parameter sets, uncertainty analysis, and visualization of calibration output are also provided. These functions are illustrated with a case study. The development of this new toolbox will facilitate calibrating the SWAT and potentially other hydrologic models in the distributed mode.