Determination of spatially differentiated water balance components including groundwater recharge on the Federal State level – A case study using the mGROWA model in North Rhine-Westphalia (Germany)

• We introduce a model for highly resolved simulations of water balance quantities.
• Soil moisture dynamics is simulated using a multi-layer soil water balance module.
• The model has been successfully applied on the Federal State level in Germany.
• The groundwater recharge map is used in regional water resources management.
• Groundwater withdrawals in NRW do not exceed groundwater recharge in large areas.

Study region: The Federal State of North Rhine-Westphalia (NRW), Germany.Study focus: On behalf of the Federal State Agency for Nature, Environment and Consumer Protection of North Rhine-Westphalia, Germany (LANUV) the mGROWA model is applied, in order to simulate the water balance components actual evapotranspiration, total runoff, direct runoff and groundwater recharge at Federal State level. mGROWA-simulations were performed in daily time steps for the hydrological reference period 1971–2000 and in a spatial resolution of 100 by 100 m. mGROWA results for groundwater recharge and State-wide recorded groundwater withdrawal rates have been used to assess the extent of groundwater exploitation in NRW.New hydrological insights: Simulated groundwater recharge levels are presented as long-term annual averages and as long-term monthly values in order to indicate the seasonal fluctuation of groundwater recharge rates. Quantitative statistics indicate that mGROWA enables the simulation of total runoff and groundwater recharge without significant tendency of over- or underestimation. Against this background mGROWA simulation results are used by LANUV to support regional water resources management, e.g. for determining the status of groundwater exploitation in NRW. The majority of groundwater bodies in NRW are at present not at risk of unsustainable groundwater usage. A small number of groundwater bodies along the river Rhine, however, have been assessed as being close to unsustainable groundwater exploitation.