Hydrogeological map of Lower Saxony 1: 50 000 — Average monthly groundwater regeneration rate 1981-2010 in April, method mGROWA18

Groundwater is a raw material that can regenerate and renew itself. The main supplier for the groundwater supply is precipitation water leaking in Lower Saxony. It ensures that the groundwater deposits of the storage rocks are replenished in the underground. The groundwater formation is particularly high in winter, as at this time a large part of the rainfall in the soil is leaking. In the warmer seasons, on the other hand, much of the precipitation already evaporates on the surface or is absorbed by plants. New groundwater formation is not the same everywhere. It depends, among other things, on the amount and distribution of precipitation, the air temperature, the characteristics of the soil, the land use (growth, degree of sealing), the relief of the land surface and the groundwater fluid level. Since these parameters differ significantly in the smallest area in Lower Saxony, the groundwater regeneration rate is also subject to large lateral fluctuations. To determine the rate of groundwater regeneration, there are different methods. These maps show the area-differentiated designation of the mean groundwater regeneration rates calculated using the mGROWA18 method (short for “monthly large-scale water balance”) (see ERTL et al. 2019). The model mGROWA was developed for the large-scale simulation of the water balance at Forschungszentrum Jülich in cooperation with the LBEG and was updated methodically for Lower Saxony and Bremen since 2016. In addition, a number of new input data were used to provide an up-to-date data base for water management planning work and water law approval procedures. MGROWA18 provides groundwater renewal rates for the periods 1961-1990, 1971-2000 and 1981-2010 as annual mean values and monthly mean values. 1:50,000 raster data (*.asc) and shape files (ESRI *.shp) are offered in scale. The new groundwater formation stages are indicated for the annual mean values in increments of 50 mm/a and for the monthly mean values in increments of 20 mm/month.