Coupled atmospheric, hydrodynamic, and hydrologic models for simulation of complex phenomena




Choudhary, Gajanan Krishna

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Simulating the interplay between atmospheric, ocean, and overland physics is often too complicated for any single model to handle due to limitations on developmental and computational costs. A variety of models that specialize in specific physics exist, such as 2D and 3D shallow water and transport models in ADvanced CIRCulation (ADCIRC) and Adaptive Hydraulics (AdH) for ocean and estuarine dynamics, Gridded Surface Subsurface Hydrologic Analysis (GSSHA) and Hydrologic Engineering Center's (HEC) River Analysis System (HEC-RAS) for 2D/1D overland flow, and Global Forecast System (GFS) and North American Mesoscale Forecast System (NAM) for atmospheric physics. This dissertation explores strong and weak coupling between different models to simulate complex phenomena that they cannot individually handle. One-way weak coupling from atmospheric models to ocean or overland flow models is already ubiquitous in the form of usage of meteorological forcing on the flow models. Coupling between 2D and 3D shallow water models including baroclinic transport, and between shallow water and overland flow models remain relatively unexplored. Strong coupling between 2D and 3D shallow water and baroclinic transport models is the major focus of this work. On studying multiple verification and validation cases, and applications testing the limits of 2D-3D coupling, it is concluded that strongly coupled 2D and 3D shallow water and transport models are conservative, stable, accurate, and convergent in line with theory, and are able to simulate physics that solely 2D or 3D models cannot in general. They also enable building computationally cheaper 3D models by enabling replacement of non-critical 3D regions with 2D subdomains. The second focus of this work is weak one/two-way coupling between 2D shallow water and 2D/1D overland flow models, which are in turn driven by one-way coupling from an atmospheric model. Two-way coupled models are shown to be conservative and capable of simulating compound flooding effects. An application of the coupled models to simulate flooding in Houston, Texas, due to Hurricane Harvey of August 2017 is presented, the results of which demonstrate the suitability of the models for use in high-fidelity forecasts of flooding during hurricanes, after some improvements.


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