Automatic calibration and improvements on an instream chlorophyll a simulation in the HSPF model

•Instream Chl a simulation in HSPF was improved using automatic calibration and model refinement•Sets of sensitive model parameters for flow, water temperature, nutrients and Chl a were suggested•The complex random factorization algorithm was effective in the automatic calibration of HSPF•Three formulations on the growth-temperature relationship of phytoplankton were evaluated•The exponential growth-temperature relationship better simulated the excess Chl a concentrations