Hydrogeological map of Lower Saxony 1: 50000 – Change of mean annual groundwater regeneration for the 30-year period 2021-2050 to 1971-2000 in the hydrological summer half-year No climate protection scenario (RCP8.5)

The map shows the modeled change in mean annual groundwater formation for the 30-year period 2071-2100 to 1971-2000 in the hydrological summer half-year (May-Oct.) in mm/a calculated with the “no-climate protection” scenario (RCP8.5).
Groundwater is a raw material that can regenerate and renew itself. The main supplier of groundwater supplies is rainwater leaking in Lower Saxony. It ensures that the groundwater deposits of the storage rocks are replenished in the underground. The new groundwater formation is particularly high in winter, as at this time a large part of the rainfall is leaking in the soil. In the warmer seasons, however, a large part of the precipitation evaporates on the surface or is absorbed by plants.
The formation of groundwater is widely distributed in different areas. It depends on the distribution of precipitation and evaporation, the characteristics of the soil, the land use (growth, degree of sealing), the relief of the land surface, the artificial drainage by drainage, the groundwater level and the properties of the near-surface rocks. Since these parameters differ significantly in Lower Saxony, in some cases in the smallest space, the formation of groundwater is also subject to large lateral fluctuations.
In order to determine the new formation of groundwater, there are various methods. The present maps show the area-differentiated designation of the mean groundwater formation, which was calculated using the mGROWA method (short for “monthly large-scale water balance”). The model mGROWA was developed for the large-scale simulation of the water balance at Forschungszentrum Jülich in cooperation with the LBEG (Herrmann et al. 2013) and since 2016 for Lower Saxony updated methodologically. In addition, a number of new input data was used to provide an up-to-date data base for water management planning work and water licensing procedures.
Daily and monthly climate projection data were used as climatic input data. The climate projection data represent the results of an ensemble of different climate models (the Lower Saxony climate ensemble AR5-NI v2.1 see Hajati et al. (2022)). The data was provided by the German Weather Service. The data is based on the EURO-CORDEX Ensemble (Jacob et al., 2014). Within the framework of the BMVI expert network, the DWD scaled down from a 12.5 km to a 5 km grid.

The climate models are powered by the “No Climate Protection” scenario (RCP8.5). This is a scenario of the IPCC, which describes a continuous increase in global greenhouse gas emissions, which by the end of the 21st century generates an additional radiative forcing of 8.5 watts per m² compared to pre-industrial levels.
The results of all climate models are equally likely. Therefore, in addition to the mean that shows a tendency, the upper (maximum) and lower (minimum) edges of the result bandwidth can be retrieved via the MapTip.
For better regionalisation, the climatic input parameters of precipitation and potential evaporation with bilinear interpolation were scaled down to a 500 x 500 m grid for mGROWA22.