Global system of rivers:: Its role in organizing continental land mass and defining land-to-ocean linkages

The spatial organization of the Earth's land mass is analyzed using a simulated topological network (STN-30p) representing potential flow pathways across the entire nonglacierized surface of the globe at 30-min (longitude x latitude) spatial resolution. We discuss a semiautomated procedure to develop this topology combining digital elevation models and manual network editing. STN-30p was verified against several independent sources including map products and drainage basin statistics, although we found substantial inconsistency within the extant literature itself. A broad suite of diagnostics is offered that quantitatively describes individual grid cells, river segments, and complete drainage systems spanning orders 1 through 6 based on the Strahler classification scheme. Continental and global-scale summaries of key STN-30p attributes are given. Summaries are also presented which distinguish basins that potentially deliver discharge to an ocean (exorheic) from those that potentially empty into an internal receiving body (endorheic). A total of 59,122 individual grid cells constitutes the global nonglacierized land mass. At 30-min spatial resolution, the cells are organized into 33,251 distinct river segments which define 6152 drainage basins. A global total of 133.1 x 10(6) km(2) bear STN-30p flow paths with a total length of 3.24 x 106 km. The organization of river networks has an important role in linking land mass to ocean. From a continental perspective, low-order river segments (orders 1-3) drain the largest fraction of land (90%) and thus constitute a primary source area for runoff and constituents. From an oceanic perspective, however, the small number (n = 101) of large drainage systems (orders 4-6) predominates; draining 65% of global land area and subsuming a large fraction of the otherwise spatially remote low-order rivers. Along river corridors, only 10% of land mass is within 100 km of a coastline, 25% is within 250 km, and 50% is within 750 km. The global mean distance to river mouth is 1050 km with individual continental values from 460 to 1340 km. The Mediterranean/Black Sea and Arctic Ocean are the most land-dominated of all oceans with land:ocean area ratios of 4.4 and 1.2, respectively; remaining oceans show ratios from 0.55 to 0.13. We discuss limitations of the STN-30p together with its potential role in future global change studies. STN-30p is geographically linked to several hundred river discharge and chemistry monitoring stations to provide a framework for calibrating and validating macroscale hydrology and biogeochemical flux models.