River Networks for Global Flow Routing Modeling

An algorithm for determining river networks for large-watershed flow routing modeling has been developed and implemented at a global and continental scale. After subdividing the terrain into square and identical cells by overlaying a coarse-resolution grid on top of it, the algorithm determines the downstream cell of each cell, and the distance along the meandering flow paths between them. Depending on the level of detail necessary for a specific application, the cell sizes can range from the hundreds of meters to the hundreds of kilometers. The method improves with respect to previously developed methods in that it uses fine-resolution vector river networks as the source of information of the flow patterns, rather than digital elevation models (DEMs). In general, it seems natural to use river networks to determine river networks of a coarser resolution, but, in addition to that, fine-resolution vector river networks tend to be more accurate than DEMs. Use of fine-resolution vector river networks has also the advantage that they capture, not only the topographic features of the terrain, but also the hydrologic ones, such as dry areas where no stream can be found even though a contributing drainage area can be delineated. River networks with resolutions of one degree for South America and 2.8125 degrees for the globe were determined to test the algorithm. Overall, the algorithm proved to capture well the flow and drainage divide patterns, and estimated basin areas were close to documented values. However, river lengths were consistently underpredicted, although a significant improvement was made when meandering factors - a unique feature of this method for better estimation of flow distances - were implemented.