Evaluation of pressures in European river basins reported under the Water Framework Directive: potentials for collaborative improvement of assessments in transnational water management.

The Water Framework Directive 60/2000/EC requires European Union member states to ensure good status of water bodies. To this end, it requires to identify relevant pressures (e.g. diffuse pollution) on waters, to address them through appropriate measures (e.g. enforce good agricultural practices), and to report both pressures and measures to the European Commission (EC). In spite of existing assessment guidance, member states report about pressures in a rather heterogeneous way. This has stimulated the EC to undertake a comparison between the pressures reported by the member states with those depicted by Europe-wide model-based indicators. This alone has required turning model results to communicable maps to be used in a decision making context with minimal risk of interpretive distortion. The comparison suggests that the identification of relevant pressures at the continental scale is not always the same as at the national and regional scale, causing difficulties in the prioritization of investments and doubts about the effectiveness of envisaged measures. A simple rank-based classification has been used to map the level of agreement between pressures reported by the member states and the corresponding European indicators, highlighting regions where a more detailed insight is required in order to come to a shared judgment on pressures hampering the achievement of good water body status. Reported pressures may suffer from incompleteness and semantic uncertainty, while European indicators suffer from model uncertainties and errors. A discussion of differences between European indicators and river basin assessments in the light of agreed-upon reporting and model limitations may help to collaboratively improve the assessment from both sides, and consequently to design more effectively the measures to be implemented at the respective levels. We present and discuss the case study, highlighting how the approach may be useful in contexts of transnational water management.