Why is uncertainty important?

Role of modelling within the context of the Water Framework Directive

Models describing water flows, water quality, ecology and economy are being developed and used in increasing number and variety. With the requirements imposed by the WFD the trend in recent years to base water management decisions to a larger extent on model studies and to use more sophisticated models is likely to be reinforced. It is important to note that the modelling studies typically do not address the entire water resources management decision process, such as the WFD process, but rather support certain elements of the process.

The role of modelling as part of the WFD process may be illustrated schematically as in Fig. 2. The inner circle in Fig 2 depicts a simplified version of the WFD planning process (EC, 2004a) with the main elements:

·        Identification including assessment of present status, analysis of impacts and pressures and establishment of environmental objectives. Here modelling may be useful for example for supporting assessments of what are the reference conditions, for assessment of the pressures and what are the impacts of the various pressures in combination to monitoring data and expert judgement (EC, 2004b).

·        Designing including the set up and analysis of programme of measures designed to be able in a cost effective way to reach the environmental objectives. Here modelling will typically be used for supporting assessments of the effects and costs of various measures under consideration.

·        Implementing the measures. Here on-line modelling in some cases may support the operational decisions to be made.

·        Evaluation of the effects of the measures on the environment. Here modelling may support the monitoring in order to extract maximum information from the monitoring data, e.g. by indicating errors and inadequacies in the data and by filtering out the effects of climate variability.

This main WFD process is a participatory process with important elements of public participation.

Modelling can be used as a tool at various stages of the WFD process, as illustrated by the four smaller circles in Fig. 2. The typical steps and elements of a modelling process are illustrated in Fig. 3 and briefly described in Chapter 2. The most important interactions between the modelling process and the main planning process are:

·         The modelling process starts with a thorough framing of the problem to be addressed and definition of modelling objectives and requirements for the modelling study (Step 1 in Fig. 3). Water managers and stakeholders dominate this step, which basically is identical to part of the broader planning process. A participatory based assessment of the most important sources of uncertainty for the decision (WFD) process should be used as a basis for prioritising the elements of the modelling study. The uncertainty assessments made at this stage will typically be qualitative.

·         The main modelling itself is composed of steps 2,3 and 4 of Fig 3. Here the link with the main planning process consists of dialogue, reviews and discussions of preliminary results involving water managers and, according to decisions made at the start of the modelling, some stakeholders. As the modelling process proceeds uncertainty assessments are typically made more quantitative (rather than qualitative) and the uncertainties assessed by the modeller are confronted with the water manager and stakeholder expectations to accuracy.

·         The finalisation of the modelling study (equivalent to the last step in Fig. 3), typically including scenario simulations. Here the water managers and the stakeholders again have a dominant role. The decisions made at the outcome of this step on the basis of modelling results are made in the context of the main planning process. Uncertainty assessment of model predictions is a crucial aspect of the modelling results and should be communicated in a way that is accessible for the stakeholders in the further WFD process.

Fig. 2 The role of modelling in the water resources management process within the context of the Water Framework Directive (WFD).

Overview