The method according to Meßer is based on the converted water balance equation:
Groundwater recharge: It will be calculated in SPRING from all input data and assigned to the attribute FLAE (column 16: "*") in the unit m³/m²/a. The time unit "year" is required in the model file.
Precipitation: Precipitation in m/year for all elements or m³/m²/TU element-wise (column 16: „*“) (attribute NIED).
Total evaporation: The total evaporation rate is taken into account depending on the climate zone, the land use, the soil type and the class of the depth to water table.
Direct runoff: The still available water from the difference between precipitation and evaporation is then reduced by the direct runoff. Besides the parameters soil type and land use on farm- and grassland the relief energy or the slope is needed. The definitive slope is the maximum slope between two nodes of an element. The program computes this value automatically from the ground level (attribute ).
A detailed description of this method is given on this website:
Input data