Infiltration
… Soils, depending on current conditions, have a capacity or ability to infiltrate precipitation, allowing water to move from the surface to the subsurface.
... "physically based” -> soil porosity, depth of soil column, saturation levels, and soil moisture.
… The infiltration capacity of the soil column is usually expressed in terms of length per time (i.e. inches per hour).
… As more water infiltrates, the infiltration generally decreases, thus the amount of water that can be infiltrated during the latter stages of a precipitation event is less than that at the beginning of the event.