There are two different approaches when producing a simulation. The first is a “historic” simulation where the current model states are set once and the model is allowed to run through the entire period of record, regardless of the number of years. The model states are allowed to become wetter or drier depending on the simulation.
As shown in the graphic, the start conditions are set, then the model is allowed to run for all years. The result is a hydrograph covering several years.