Approaches to continental scale river flow routing

Recent concerns about global climate change and a series of large-scale hydrologic events such as the Mid-West flood of 1993 and the El Nino of 1997 have focused attention on the need to track the flow of water through the entire hydrologic cycle. On the land surface, databases of routing parameters and routing models are required to describe the movement of runoff generated by Global Circulation Models (GCMs) and other soil water balance models over the earth's surface. In this study, a terrain analysis is performed using 30 arcsecond Digital Elevation Model (DEM) data to develop a global database of terrain derived routing parameters. A computationally efficient grid based routing model, called a source to sink (STS) model, is implemented in this study. It routes flow directly from the point of generation to the desired observation point. The STS model also allows for easy interaction with models of other phases of the hydrologic cycle by incorporating the boundaries of their modeling units into the definition of its own modeling units. A continental scale STS model is created and parameterized for each continent using datasets derived from the terrain analysis. A process is defined for determining additional velocity and dispersion parameters from observed flow data. Another continental scale routing model is developed using the watershed based approach of the Hydrologic Modeling System (HMS). Hydrologic elements and routing parameters for the HMS model are derived from the same terrain data used in parameterizing the STS model. Basin responses from the two models are compared for various spatial and temporal resolutions and parameter distributions to determine the implications of their respective conceptual models. These comparisons show that basin responses in the STS model are relatively independent of spatial and temporal scale while the HMS model is scale dependent with regard to both spatial and temporal resolution. Basin responses for a fine resolution HMS models were successfully duplicated in a STS model for both the uniform and non-uniformly distributed velocity and dispersion parameter case.