Revisiting At-a-Station Hydraulic Geometry Using Discharge Observations and Satellite-Derived River Widths

Abstract

The power-function exponent b of at-a-station hydraulic geometry (AHG) depicts the temporal response of river hydraulic parameters to changing discharge and is crucial for hydraulic modeling, habitat assessment, and river management. However, previous research, limited by field measurements, offers only a fragmentary understanding of the AHG exponent b in confined areas. Additionally, it remains challenging to establish the correlation between b and the climatic regime of a river. To offer a more comprehensive scope of AHG, this study assesses the width–discharge AHG exponents of 1,568 river reaches by pairing multi-temporal river width data from 1.19 million Landsat images with discharge observations from >17,000 gauge stations worldwide. The results show that b has a median value of 0.213, consistent with values reported in previous regional studies, but it exhibits complex relationships with 3 spatial dimensions—latitude, elevation, and drainage area. We further analyze the spatial variations in b against >200 physiographic and climatic factors, and find that reaches characterized by cohesive soil, high forest coverage, and less anthropogenic influences typically exhibit lower values of b, indicating a weaker response of width to discharge changes. By labeling 4 planimetric river morphologic types globally, we show that braided reaches exhibit the highest median of b, followed by straight, anabranching, and meandering reaches. The differences can be well explained by the climatic conditions of the river reaches as shown on the Budyko curve. This study lays the foundation for AHG research in ungauged regions using satellite remote sensing, expanding global hydraulic data and enhancing the understanding of the spatial variability and influencing factors of hydraulic geometry worldwide.