For Managers: Integrated catchment modelling as a management tool

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A modelling framework has been developed that takes integrated scenarios of climate, land management, water use and atmospheric deposition change as input to biophysical catchment models that represent connected river-lake-wetland systems, and determines the long-term, and is some cases, seasonal changes in flow and water quality and key ecological indicators. This framework is applicable on a catchment-by-catchment basis and thereby considers the nuances of each and is compatible with the basic management unit on which the Water Framework Directive is based: the river catchment. The parameter sets from the model applications will be made available allowing others to use the models with some idea of parameters that can be left ‘as factory settings’ and suggested parameter ranges for certain catchment types. The biophysical modelling framework has been used in conjunction with cost-effectiveness analysis to identify which measures will best help reduce nutrient pollution today and fifty years hence when set against the background of projected environmental change. A new generation of models, based on Bayesian Networks, have been trialled to incorporate multiple stresses on key ecological indicators.

The catchment biophysical monitoring highlighted a paucity of baseline flow, water quality and biological data in southern Europe. It is recommended that the EU provide the resources to support environmental monitoring in this region which is most at risk from the direct impacts of climate change. In REFRESH case studies for these regions, nutrient water quality appears of secondary importance to flow and other water quality elements, such as salinity and water temperature.

The general picture presented from the catchment modelling is that the predicted effects on waters differ between the northern and southern sites. In the north and mid-latitudes, the increased temperatures are balanced to some extent by increased precipitation, leading to relatively small effects on water flows, though seasonal effects may still be important. In the south, increased temperatures and lower precipitation act in the same direction to reduce water flows considerably. In the case of Lake Beysehir, this may even lead to the lake drying up in the foreseeable future, and this effect would far outweigh any nutrient-related problems. In general, the effects of climate change alone on nutrient concentrations are rather small. The effects of credible land use changes are rather larger, and generally, the land use changes representing future “environment-focussed” storylines (B1 and B2) reduce nutrient concentrations, and those from the “economic, market driven” storylines (A1 and A2) increase them. However, there are exceptions and considerable differences in response between sites. The responses seem more dependent on the mixture of nutrient sources (e.g. agriculture versus wastewater) than the degree of climate change. Modelled ecological changes are not generally proportional to the changes in nutrients. Ecological change can be less than the nutrient change (e.g. chlorophyll at Lake Beysehir and the Orlik Reservoir in the Czech Republic) or greater due to a complex set of reactions in the food web (e.g. at the IJsselmeer). Modelled mitigation options can reduce nutrients, and there is no evidence here that they are less effective under a future climate. With less certainty, mitigation options can affect the ecological status of waters at these sites in a positive manner leading to an improvement in Water Framework Directive status at some sites. Uncertainty in the climate models, as represented by the differences between the three GCM-RCM combinations used in this study, does not affect this overall picture much, though there are differences at individual sites.

Mitigation measures were generally effective in reducing nutrient concentrations in current climates. Mitigation strategies were generally aimed at improving ecological outcomes and hence tended to target P. Reductions in nitrate concentrations were therefore much lower than those of total P and SRP. Mitigation strategies continued to work with future climates, though in some cases the effects were small. The initial status of the sites covered a wide range of WFD categories. Mitigation gives a general reduction in risk, and can cause sites to cross boundaries between WFD classes in a favourable direction.