Incremental Improvements in Chesapeake Bay Environmental Model Package

The performance of the Chesapeake Bay Environmental Model Package is examined in four steps of model development. The steps include initial application, grid refinements, addition of living resources, and grid refinements with recalibration. Performance statistics are presented for the mainstem bay and for the James River, a major tributary. Computed salinity has the lowest relative error. Computed total phosphorus and surface chlorophyll have the greatest relative error. Errors in the bay are lower than in the James River. The capacity of the model has increased substantially over more than a decade but quantitative performance, measured by the summary statistics, has reached a plateau. Limited spatial sampling, uncertainty in loading, and difficulty in assigning boundary conditions are among the factors that limit the accuracy that can be attained with the model.