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The commonly used discretization approaches for distributed hydrological models can be broadly categorized into four types, based on the nature of the discrete components: Regular Mesh, Triangular Irregular Networks (TINs), Representative Elementary Watershed (REWs) and Hydrologic Response Units (HRUs). In this paper, a new discretization approach for landforms that have similar hydrologic properties is developed and discussed here for the Integrated Hydrologic Model (IHM), a combining simulation of surface and groundwater processes, accounting for the interaction between the systems. The approach used in the IHM is to disaggregate basin parameters into discrete landforms that have similar hydrologic properties. These landforms may be impervious areas, related areas, areas with high or low clay or organic fractions, areas with significantly different depths-to-water-table, and areas with different types of land cover or different land uses. Incorporating discrete landforms within basins allows significant distributed parameter analysis, but requires an efficient computational structure. The IHM integration represents a new approach interpreting fluxes across the model interface and storages near the interface for transfer to the appropriate model component, accounting for the disparate discretization while rigidly maintaining mass conservation. The discretization approaches employed in IHM will provide some ideas and insights which are helpful to those researchers who have been working on the integrated models for surface-groundwater interaction.
