engleski

The role of numerical models in environmental studies

During the last few decades accuracy of the ocean hydrodynamic models tremendously increased due to the increased computer power and due to our increased understanding of marine dynamics, subgrid scale parameterisations and numerics. The practice of numerical modelling is growing rapidly also due to increased understanding of the limitations of the alternative and more traditional methodologies of making field measurements and developing analytic theories of highly nonlinear dynamical systems. Environmental studies require accurate knowledge of the marine environment dynamics. Field measurements in oceanography are usually complex and expensive, and in general result with sparse data sets compared to requirements. One of the important task for numerical models is to help marine scientists and practitioners to overcome insufficient space and time resolution of the collected data. Numerical hydrodynamic models are mathematical formulation on basic physical laws (Newton’s Laws, conservation principles) applied for marine systems. They provide information of three dimensional circulation and density fields and are used to improve our understanding of ecosystem and to predict its future state. Ocean models consist of set of partial differential equations which due to turbulent nature of the sea circulation, complicated shape of basins and strong nonlinearity of the marine system cannot be solved using known analytic methods. The equations require numeric computational methods using discretized equations on finite grid. In oceanography models can be used for scientific research in process oriented studies and realistic simulations, and in various application studies. In both cases the objective of the numerical model is to predict the future state from the knowledge of the present state by use of the dynamical equations. To fulfil this objective the following information is required: (1) the initial state of the field variables, (2) a closed set of prediction equations relating the field variables, (3) a method of integrating the equations in time to obtain the future distribution of the field variables. One of the greatest advantages of the models for the environmental studies is their possibility to predict future hypothetical state and aid in strategic decisions related to marine environment. Precise and well defined model can predict the influence of the planned coastal infrastructure on circulation and ecosystem. In general, impact of all changes in the marine ecosystem that can be numerically formulated can be assessed by modelling system. But nevertheless, numerical model results due to the used numerical techniques and parameterization of the sub-grid scale processes which affect their accuracy should be considered with particular care. Having in mind limitations of both measurements and numerical models, design of optimal assessment study should incorporate both components. Careful selection of the sampling sites and frequencies and appropriate modelling system can give the best results with significantly reduced expenses. Various accomplishments and possibilities of numerical models in environmental studies will be illustrated through examples of oil spill modelling, sewage system impacts and early fish stage dynamics, all based on ROMS hydrodynamic model.

modelling, environmental study, prediction, coastal circulation, ROMS

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