Global River Topology (GRIT): A Bifurcating River Hydrography

Abstract

Existing global river networks underpin a wide range of hydrological applications but do not represent channels with divergent river flows (bifurcations, multi-threaded channels, canals), as these features defy the convergent flow assumption that elevation-derived networks (e.g., HydroSHEDS, MERIT Hydro) are based on. Yet, bifurcations are important features of the global river drainage system, especially on large floodplains and river deltas, and are also often found in densely populated regions. Here we developed the first raster and vector-based Global RIver Topology that not only represents the tributaries of the global drainage network but also the distributaries, including multi-threaded rivers, canals and deltas. We achieve this by merging a 30 m Landsat-based river mask with elevation-generated streams to ensure a homogeneous drainage density outside of the river mask for rivers narrower than approximately 30 m. Crucially, we employ the new 30 m digital terrain model, FABDEM, based on TanDEM-X, which shows greater accuracy over the traditionally used SRTM derivatives. After vectorization and pruning, directionality is assigned by a series of elevation, flow angle and continuity approaches. The new global network and its attributes are validated using gauging stations, comparison with existing networks, and randomized manual checks. The new network represents 19.6 million km of streams and rivers with drainage areas greater than 50 km2 and includes 67,495 bifurcations. With the advent of hyper-resolution modeling and artificial intelligence, GRIT is expected to greatly improve the accuracy of many river-based applications such as flood forecasting, water availability and quality simulations, or riverine habitat mapping.

Key Points

• Existing large-scale river networks only represent single-threaded gravity flow paths, rather than observed river centerlines
• Global RIver Topology (GRIT) was created by merging the 30 m Landsat-based river mask from Global River Widths from Landsat with elevation streams, using the new 30 m FABDEM for greater accuracy
• GRIT is the first branching global river network representing bifurcations, multi-threaded channels, and canals
  
  Plain Language Summary
  Global river maps often overlook complex features, such as when a single river channel splits into multiple channels. These branching river systems are important because they are often found in densely populated, often flood-prone regions, and they are crucial for understanding water movement across the Earth's surface. To address this limitation of existing river maps, we developed a new global river network called Global RIver Topology (GRIT), which includes these branching rivers and channels. GRIT was created by combining high-resolution satellite imagery of rivers with advanced elevation data of the earth's surface. GRIT not only includes the main river channels but also provides information on river flow directions, widths, and points where rivers split. The GRIT river network has a total length of 19.6 million km and includes 67,495 bifurcations. GRIT stands to significantly enhance applications in hydrology, ecology, geomorphology, and flood management.