SURFACE-WATER FLOW IN LANDSCAPE MODELS - I - EVERGLADES CASE-STUDY

Many landscape models require extensive computational effort using a l arge array of grid cells that represent the landscape. The number of s patial cells may be in the thousands and millions, while the ecologica l component run in each of the cells to account for landscape dynamics is often process based and fairly complex. To compensate for the incr eased computational complexity of the model there is a tendency to sim plify the hydrologic component that fluxes material horizontally acros s the landscape. Instead of full scale hydrologic models based on stab le implicit schemes, computationally simpler explicit algorithms are i ncorporated and run with quite large time steps. As a result some fair ly inadequate behavior may be observed, especially when the temporal a nd spatial steps are modified without due care. We illustrate these pr oblems with a series of runs performed using the Everglades Landscape Model (Southern Florida, USA), that covers an area of more than 10000 km(2). Several algorithms for hydrologic fluxing are compared in terms of their computational complexity and stability. We argue that a comp romise can be drawn by supplementing the explicit modeling scheme with a series of additional checks and conditions that provide for model s tability, and with some empirical assumptions that allow the model to operate over a sufficiently large range of temporal and spatial scales . (C) 1998 Elsevier Science B.V. All rights reserved.