Evaluating catchment-scale models for diffuse pollution policy support: some results from the EUROHARP project

The EU Framework V EUROHARP project evaluated the performance of a representative range of nutrient pollution tools used for policy support across a network of six representative catchments covering a north–south gradient in climate, hydrology, soils, and land use. The main objective was a detailed evaluation of model performance, strengths and weaknesses, and ranges of applicability. Model performance was assessed against measured data by an expert group. A range of models was tested and compared, including the EveNFlow model of daily flow and nitrate concentrations, and the PSYCHIC model of monthly total phosphorus loads.The outputs from the EUROHARP project have a number of important implications for the use of models to support diffuse pollution policy in the EU. The outcomes suggested that the policy support tools tested are capable of acceptable performance in modelling flows, nutrient concentrations and loads in five out of the six test catchments considered by the study. Results also demonstrated that diffuse pollution tools can be successfully applied to catchments where agricultural practices contrast markedly from those characterising the study areas underpinning the development of individual models. Such adaptability conveys significant benefits by demonstrating that some diffuse pollution tools have the flexibility required for demanding and strategic policy support purposes.