The development of rainfall-runoff relationships has gone through a sequence of methodolgies.
Early in this development, the goal was to focus on storm runoff using procedures such as the Antecedent Index.
As the limitations of such procedures became apparent and computer methodology developed, there was a continuing attempt to define additional elements of the hydrologic cycle through increasingly complex formulations.
Many of these attempts to simulate runoff and resultant streamflow continued to focus on the streamflow simulation, with little consideration of the soil moisture characteristics which are responsible for streamflow production.