Influence of Scale on SWAT Model Calibration for Streamflow

The Soil Water Assessment Tool (SWAT) was implemented in the 281,000 ha St. Joseph River Watershed (SJRW) to investigate the influence of multiple scales on stream flow model calibration parameters (Fig.1). The relationship between model calibration parameters and associated hydrological response units (HRU) between different scales is not well understood. In this investigation, two scales were used within the SJRW where such factors as land use, soil type, topography and management practices are considered similar, thus, conforming to the concept of downscaling rather than regionalization. The model was calibrated for streamflow in the SJRW. Critical parameters optimized for calibration were: 1) CN2, curve number, 2) ESCO, soil evaporation compensation factor, and 3) SOL_AWC, available water holding capacity. Using optimized parameters at the SJRW scale, stream flow estimates were evaluated in the 70,820 ha Cedar Creek Watershed (CCW), the largest subbasin and tributary in the SJRW. These same parameters were then optimized at the CCW scale and streamflow estimates for the CCW and the SJRW were evaluated by examination of the coefficient of determination (R) and the Nash and Sutcliffe (1970) model efficiency coefficient (ENS). Modeled and measured streamflow data were statistically analysed at both scales based on their respective calibrations.