Optimization of the SWATPlus model to adequately predict different segments of a managed streamflow hydrograph

Complete representation of rainfall-runoff responses in complex, large watersheds using a single-objective parameterization approach in watershed models is often unachievable. In this study we present a calibration approach for the SWAT+ model that independently fits model parameters for different flow segments of the hydrograph. The approach is demonstrated for the Feather River, California, USA using daily streamflow from the Lake Oroville reservoir outlet gage. Results show that when model parameters were independently fitted for different flow segments the KGE, NSE, PBIAS, and RSR values improved to 0.96, 0.99, -3.3, and 0.10, respectively, compared to 0.72, 0.66, -9.30, and 0.53, respectively, achieved under a multi-objective and full hydrograph (average hydrograph) calibration. The results highlight when considering the average hydrograph and flow duration curves, a more balanced representation of both poorly and well-performing segments is achieved, emphasizing the importance of segment-specific parameterization and multi-objective evaluation for accurately representing different flow conditions.