Rivers show a seasonal rhythm over time due to multiple processes. A critical aspect of the rhythm is the river stage, which resembles the pulse of a river as it rises and falls. River stage fluctuations play an important role in many physical-biological-chemical processes such as river morphology, benthic aquatic habitat, suspended mass and biogenic element transport, surface-to-groundwater interaction, etc. However, due to the limitation of traditional water level monitoring methods, river level data are scarce, which seriously hinders the research of related topics.

The most basic questions are, for example, to what extent the river stage fluctuates in a year, say, 5 meters, 10 meters, or even more? How much does the fluctuation vary across rivers? So far, there is no data available to answer these questions.

Assistant Professor Liguang Jiang’s research team from the School of Environmental Science and Engineering (ESE) at the Southern University of Science and Technology (SUSTech) has recently published a paper that uses satellite (Sentinel-3A & B) measurements to track the stage fluctuations of rivers during 2016-2022.

Their research work, entitled “Tracking River’s Pulse From Space: A Global Analysis of River Stage Fluctuations”, has been published in Geophysical Research Letters, a top journal in the field of geophysical research.

This study uses Sentinel-3 satellite altimetry measurements to monitor river stage fluctuations of 3272 global river virtual stations during 2016-2022 (Figure 1). The results show that in the Orinoco, Mississippi, Yangtze, Irrawaddy, and Amazon basins, the average water level fluctuated more than 7 meters. Water level fluctuations at a single site vary widely, from less than 1 meter to as high as 18 meters.

Figure 1. Distribution and statistics of river stage fluctuations on a global scale

The work highlights the influence of climate characteristics and human activities on river stage fluctuations. The research team combined the global drought index data to conduct a statistical analysis of river water level fluctuations in different climate regions (Figure 2). The results show that the fluctuation of river levels in semi-arid regions is more significant than in other climate regions, possibly because in relatively arid regions, rivers are more likely to lose water to recharge surrounding aquifers. This phenomenon implies that there is a complex interaction between rivers and groundwater in climatic arid areas, and provides an important clue for further study of surface water-groundwater interaction.

Figure 2. Global patterns (a: Sentinel-3A; (b) Sentinel-3B) of river stage fluctuation in regard to climate aridity

River fluctuation amplitude is not only affected by climate factors but also by human activities. In this study, the river connectivity status index (CSI) was used to characterize human activities and analyze the influence of human activities on river fluctuations. Using a weighted linear regression method, the research team explored the magnitude of river fluctuations across a range of connectivity indices. As shown in Figure 3, there was a significant positive correlation between fluctuation amplitude and CSI (p <0.005), and CSI explained 51.2% of water level fluctuation. This result unveils the substantial influence of human activities on river level fluctuations.

Figure 3. The relationship between river stage fluctuation amplitude and CSI

Yanan Zhao, a Ph.D. student in Assistant Professor Liguang Jiang’s research group, is the first author of the paper. Assistant Professor Liguang Jiang from SUSTech is the corresponding author, and SUSTech is the first affiliation. Co-authors include Xingxing Zhang, a researcher at the Institute of Geographic Science and Natural Resources Research, Chinese Academy of Sciences, and Junguo Liu, Chair Professor of SUSTech.

This study was supported by the Shenzhen Key Laboratory of Precision Measurement and Early Warning Technology for Urban Environmental Health Risks, Shenzhen Science and Technology Program, and the Start-Up Fund of SUSTech.

Paper link: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GL106399

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