Towards an alternative blueprint for a physically based digitally simulated hydrologic response modelling system

A critique of the Freeze and Harlan blueprint for a distributed physically based hydrological model leads to the conclusion that it will be abandoned. An alternative blueprint as a modelling methodology is proposed that explicitly recognises the potential for equifinality in scale‐dependent model representations. An inductive rather than deductive definition of physically‐based is proposed that reflects the important role of observables in constraining the feasible models.