Selecting the appropriate time step in an integrated systems model

In recent years a variety of integrated system models to support the management of water systems appeared. Two examples are the RaMCo model for coastal-zone management and WadBOS for the Dutch Wadden Sea. A key aspect of the design is that ecological, economic, and physical process models are combined in an integrated systems network. In most cases a uniform mesh size and time step are used for all models, exceptions being made for processes requiring a lower or higher level of detail. The choice for a particular model is primarily based on data availability and modeling experience rather than sound scientific principles, because an objective methodology for the selection of spatial and temporal scales in integrated system models is still lacking. In this paper we examine one aspect of model integration: the problem of how to estimate the appropriate time step for a model in an integrated systems network. The approach followed is based on the comparison of the numerical truncation error for the discrete system equations with the model uncertainties. The example discussed pertains to cockle fisheries in the Dutch Wadden Sea.