At the end of this process, the modeler is left with several models, each of which can fit a specific storm that occurring during a specific antecedent moisture condition, but none of which are capable of simultaneously fitting all of the data.
22.
It is important to note that the curve number methodology is an event-based calculation, and should not be used for a single annual rainfall value, as this will incorrectly miss the effects of antecedent moisture and the necessity of an initial abstraction threshold.
23.
An alternative approach for modeling antecedent moisture is to start from measurements of the behavior of the system and the external influences ( inputs to the system ) and try to determine a mathematical relation between them without going into the details of what is actually happening inside the system.
24.
Some modeling approaches such as the Hydrologic Simulation Program-Fortran ( HSPF ) or the Stanford Watershed Model developed by Crawford and Linsley ( 1966 ) attempt to address antecedent moisture conditions through a complex physically based representation of the transport paths of water on the surface and in the subsurface.
25.
Timing and duration of the rainfall events, as well as factors such as antecedent moisture conditions, overall watershed shape, along with subcatchment-area shapes, land slopes ( topography / physiography ), geology / hydrogeology ( i . e . forests and aquifers can serve as giant sponges that absorb rainfall and slowly release it over subsequent weeks and months ), and stream-reach lengths all play a role here.
