An Efficient Method for Mapping High-Resolution Global River Discharge Based on the Algorithms of Drainage Network Extraction

Jiaye Li,Suning Liu,Tiejian Li,Haiyun Shi

doi:10.3390/w10040533

Abstract

River discharge, which represents the accumulation of surface water flowing into rivers and ultimately into the ocean or other water bodies, may have great impacts on water quality and the living organisms in rivers. However, the global knowledge of river discharge is still poor and worth exploring. This study proposes an efficient method for mapping high-resolution global river discharge based on the algorithms of drainage network extraction. Using the existing global runoff map and digital elevation model (DEM) data as inputs, this method consists of three steps. First, the pixels of the runoff map and the DEM data are resampled into the same resolution (i.e., 0.01-degree). Second, the flow direction of each pixel of the DEM data (identified by the optimal flow path method used in drainage network extraction) is determined and then applied to the corresponding pixel of the runoff map. Third, the river discharge of each pixel of the runoff map is calculated by summing the runoffs of all the pixels in the upstream of this pixel, similar to the upslope area accumulation step in drainage network extraction. Finally, a 0.01-degree global map of the mean annual river discharge is obtained. Moreover, a 0.5-degree global map of the mean annual river discharge is produced to display the results with a more intuitive perception. Compared against the existing global river discharge databases, the 0.01-degree map is of a generally high accuracy for the selected river basins, especially for the Amazon River basin with the lowest relative error (RE) of 0.3% and the Yangtze River basin within the RE range of ±6.0%. However, it is noted that the results of the Congo and Zambezi River basins are not satisfactory, with RE values over 90%, and it is inferred that there may be some accuracy problems with the runoff map in these river basins.

Highlights

The hydrological regime of rivers is of great importance for social and economic development, such as in references [1,2,3]
Using the proposed mapping method, a global map of mean annual river discharge with a spatial resolution of 0.01 degrees is obtained. This map is produced based on the algorithms of drainage network extraction, and the river discharge values will appear along the drainage networks, and the drainage networks with the higher Strahler stream orders [42,43] will have a darker blue color, which indicates larger river discharge values
Due to the small pixel size (i.e., 0.01 degrees), the pixels with the darker blue color are generally surrounded by a mass of pixels with the lighter blue color, resulting in the global map seeming unlikely to be well displayed in a single figure when setting the spatial resolution as that suitable for printing (e.g., 300 or 600 dpi)

Summary

Introduction

The hydrological regime of rivers is of great importance for social and economic development, such as in references [1,2,3]. The global knowledge of river discharge is still poor; see references [12,13,14]. The distributed networks of gauging stations are sparse, especially in less developed countries; on the other hand, river discharge measurements are usually proprietary in many countries and cannot be shared to the public [14]. Satellite observations, which can provide spatially dense coverage and characterize river discharge variation similar to that performed at gauging stations, have been applied for mapping global river discharge; see [4,14,15,16]

Objectives

Results

Discussion

Conclusion