Is ET often oversimplified in hydrologic models? Using long records to elucidate unaccounted for controls on ET

•Over multiple decades, discharge can only be simulated with time varying parameters.•Either time-variability of a PET scalar or innate watershed parameters can be used.•Innate watershed parameters include field capacity and wilting point.•A time-variable scalar on PET is consistent with known biophysical processes.•Temporal variation in innate watershed parameters has little physical explanation.