Abstract

Groundwater is a very important source for public water supply in the Netherlands since approximately 65% of total public water supply relies on groundwater. Although fresh groundwater is available in considerably large quantities, groundwater is becoming a scarce national recource. Scarcity is mentioned with special reference to the effects of groundwater withdrawal on agricultural production and the desiccation of nature reserves. Groundwater withdrawal is one of the causes, but intensified land drainage and the regulation of surface water levels also contribute substantially to the lowering of groundwater levels. A study was carried out to analyse the impact assessment for the next decades of different groundwater extraction scenarios on the value and distribution of terrestrial ecosystems (especially with regard to vegetation). Several computer programmes have either been used or developed for this study. Throughout the project intensive use was made of the features of the Geographical Information System. The hydrological effects of changes in groundwater withdrawal have been calculated with the RIVM National Groundwater Model for the Netherlands (LGM). The changes in the amounts of inlet water were calculated with the RWS/RIZA model, DEMand GENerator (DEMGEN). The hydrological doses calculated with LGM and DEMGEN are input for the eco-hydrological Dose-Effect Model for terrestrial NATure (DEMNAT-2). With this model it is possible to predict changes in the completeness of terrestrial ecosystems within a grid cell of 1 km2. The results of this study are recorded in 15 separate reports, each covering one or more specific topics. The overall results are summarized in this particular report.