The Messer method is based on the rearranged water balance equation:

Groundwater recharge = precipitation – total evaporation – direct runoff.

• Groundwater recharge: It is calculated from the input data in SPRING and assigned to the attribute FLAE (column 16 "*") in the unit m³/m²/a. The time unit "year" in the model file is a prerequisite..

• Precipitation: Amount of precipitation entered in the unit m/year for all elements or m³/m²/TU by element (column 16: "*") (attribute NIED).

• Total evaporation: The total evaporation is taken into account depending on the climatic zone, land use, soil type and depth to the groundwater table.

• Direct runoff: The water still available from the difference between precipitation and evaporation is then reduced by the direct runoff. In addition to the parameters of soil type, depth to groundwater table and land use, the relief energy or slope is required for this. The maximum gradient between the nodes (possibly also across the diagonal) of the element is used as the decisive gradient in the finite element concerned, which the programme automatically calculates from the terrain elevation at the individual nodes).

A detailed description of this procedure can be found on this website:

A simplified method for the calculation of area-differentiated groundwater recharge in Central Europe

Input data