Deriving a global river network map and its sub-grid topographic characteristics from a fine-resolution flow direction map

D Yamazaki,T Oki,S Kanae

doi:10.5194/hess-13-2241-2009

D Yamazaki, T Oki + Show 1 more

Open Access

https://doi.org/10.5194/hess-13-2241-2009

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Abstract

Abstract. This paper proposes an improved method for converting a fine-resolution flow direction map into a coarse-resolution river network map for use in global river routing models. The proposed method attempts to preserve the river network structure of an original fine-resolution map in the upscaling procedure, as this has not been achieved with previous upscaling methods. We describe an improved method in which a downstream cell can be flexibly located on any cell in the river network map. The improved method preserves the river network structure of the original flow direction map and allows automated construction of river network maps at any resolution. Automated construction of a river network map is helpful for attaching sub-grid topographic information, such as realistic river meanderings and drainage boundaries, onto the upscaled river network map. The advantages of the proposed method are expected to enhance the ability of global river routing models by providing ways to more precisely represent surface water storage and movement.

Highlights

Global river routing models, which simulate river discharge from the land to the ocean along river networks, were developed primarily to close the hydrological cycle in climate models (e.g., Miller et al, 1994; Sausen et al, 1994)
River discharge may be considered as a renewable freshwater resource for human activities (e.g., Oki and Kanae, 2006), and global river routing models are useful for water resources assessments under the present and future climate conditions (e.g., Hanasaki et al, 2008)
The disconnection of originally continuous flow paths has been the main problem encountered with previous methods for producing an upscaled river network map

Summary

Introduction

Global river routing models, which simulate river discharge from the land to the ocean along river networks, were developed primarily to close the hydrological cycle in climate models (e.g., Miller et al, 1994; Sausen et al, 1994). Routing of runoff is useful for validating the amount and timing of runoff generation by land surface schemes in climate models (e.g., Oki et al, 1999; Hirabayashi et al, 2005). River discharge may be considered as a renewable freshwater resource for human activities (e.g., Oki and Kanae, 2006), and global river routing models are useful for water resources assessments under the present and future climate conditions (e.g., Hanasaki et al, 2008). River routing schemes adopted in these models receive discharge from upstream grid cells and route it to downstream grid cells. This requires that a river network map includes the downstream location of each grid cell. A river network map is expected to imitate the geomorphology of actual flow paths and basin boundaries for a realistic simulation of river discharge

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