The process of the (transient) calculation of recharge rates to land on the soil water balance is based on the theoretical foundations that are described in DVWK 238/1996 "Determination of evaporation from land and water areas" in detail.
For the calculation of the recharge rate on the soil water balance is the crucial role of the soil as a water reservoir by including the following components considered:
Potential evapotranspiration (ETP): evaporation from surfaces under given meteorological conditions and an unlimited mass of water available. The potential evaporation is an operand, which is determined from measured meteorological values (from: DVWK 238/1996)
Field capacity (FK): The field capacity is the water-holding capacity of the soil against the force of gravity. The field capacity is the maximum water content, that a soil can hold under natural conditions.
Permanent wilting point (PWP): The permanent wilting point describes the water content of the soil (depending on the plant), below which available water for plants no longer exists (see: Müller, Tibor: "Wörterbuch und Lexikon der Hydrogeologie"). It is therefore the lowest water content, which reached a soil under natural conditions. It depends on the soil and plant.
Usable field capacity (nFK): The part of the field capacity, which can be absorbed by plants through the roots is called the usable field capacity (see: Müller, Tibor: "Wörterbuch und Lexikon der Hydrogeologie"). The usable field capacity is thus obtained from the difference between field capacity - permanent wilting point (nFK = FK - PWP).
Effective root depth (We): The effective root depth is about 50 - 60% of the maximum root depth. It features the soil volume in which the soil water balance is affected by intensive plant water consumption.
The recharge rate calculation on to the soil water balance applies in the first place to natural undeveloped areas, but a groundwater model usually also includes built-up areas, these areas are in SPRING still considered by the method of recharge calculation by Schroeder and Wyrwich.
The recharge rate calculation on soil water balance, as it is currently implemented in SPRING, is in a development phase. Therefore, in future, certainly changes in required data or input files are possible. The current program description is always available on our hompage under the menu item "Download & Support: Manual SPRING 4.1".
Input data in the model file