Hydrogeological map of Lower Saxony 1 : 50 000 – average annual groundwater recharge for the 30-year period 2071-2100 in the hydrological winter half-year, climate change mitigation scenario (RCP2.6)
Description
The map shows the modelled average annual groundwater recharge for the 30-year period 2071-2100 in the hydrological winter half-year (Nov.-Apr.) in mm/a calculated using the ‘climate protection’ scenario (RCP2.6).
Groundwater is a raw material that can regenerate and renew itself. The main supplier for the groundwater supply is rainwater that seeps into Lower Saxony. It ensures that the groundwater deposits of the storage rocks in the subsoil are replenished. Groundwater recharge is particularly high in winter, as a large proportion of precipitation seeps into the soil at this time. In the warmer seasons, however, a large part of the precipitation already evaporates on the surface or is absorbed by plants.
Groundwater recharge is spatially very differently distributed. 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 characteristics of the near-surface rocks. Since these parameters differ significantly in Lower Saxony, in some cases in the smallest of spaces, groundwater recharge is also subject to large lateral fluctuations.
There are various methods for determining groundwater recharge. The available maps show the area-differentiated designation of the mean groundwater recharge, 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 methodologically updated for Lower Saxony since 2016. In addition, a number of new input data were used to provide an up-to-date data basis for water management planning work and permitting procedures under water law.
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 (see Hajati et al. (2022)). The data was provided by the German Weather Service. This is based on data from the EURO-CORDEX Ensemble (Jacob et al., 2014). As part of the BMVI network of experts, the DWD scaled down from a 12.5 km to a 5 km grid.
The climate models are driven by the ‘climate change mitigation’ scenario (RCP2.6). This is a scenario of the IPCC (Intergovernmental Panel on Climate Change), which means significant efforts in climate protection and low emissions.
The results of all climate models are equally likely. Therefore, in addition to the mean, which shows a trend, the upper (maximum) and lower (minimum) edge of the result bandwidth can also be retrieved via the MapTip.
For better regionalization, the climatic input parameters precipitation and potential evaporation with bilinear interpolation were scaled down to a 500 x 500 m grid for mGROWA22.