Towards a General Water Balance Assessment of Europe

Large proportions of water supply in European countries rely on groundwater resources, and many aquifers in water scarce regions are overexploited. Water management relies on reasonable information on water availability as well as on water demands by different sectors. Information on water availability and water needs are crucial to identify hot spots of quantitative pressures on water resources. This report focuses on estimating natural water availability across Europe. Simple water balance models were applied for an assessment of available water and potentials and limitations of their application are shown. Special emphasis is given to the role of groundwater in the water cycle and we explore ways to derive groundwater balance terms for large scale assessments. We further develop indicators of water quantity pressure relating water availability to water use and losses at different spatial scales. A short overview on the functioning of groundwater systems is given, highlights properties, processes and problems relevant for groundwater quantity and quality assessment. Some concepts to address groundwater issues at large scale are derived. The methodological part combines a general water balance assessment at large scale with more specific approaches to characterize groundwater systems and to quantify groundwater balance terms at large scale. Two different water balance modelling approaches are applied estimating the amount of water available for direct and subsurface runoff. The modelling approaches are compared to observed values and to each other. The available water is compared to water abstractions developing to indicators for human pressures on water resources. Focusing more specifically on groundwater systems, different methods to calculate baseflow and groundwater recharge are applied and compared and a prototype groundwater recharge map of Europe is presented. The report concludes with a synthesizing discussion of methods and results and an outlook on possible future studies. The individual studies have not yet been integrated into a common framework. Rather, they show various restrictions that require further research on various specific issues relevant for water management at European scale. The approaches laid out in this report and related reports provide a starting point for further development of screening approaches to be integrated in a common water resources assessment framework.JRC.H.5-Rural, water and ecosystem resource