The impact of river plumes on the sea-level variability

Abstract

In the face of climate change and changing sea levels, it is important to understand the different drivers of sea-level variability. Tides and atmospheric forcing are the major drivers of sea-level variability, while steric contributions are often neglected in shallow coastal and shelf seas. Here, we investigate the impact of the Rhine River plume on the sea surface height in the North Sea. Because the river plume is modulated by the tides, steric changes coincide with tidal signals. Therefore, they are hard to observe directly using tide gauge measurements or satellite altimetry. Here, we use a 3D hydrodynamic model, allowing us to quantify the steric contribution. We find steric contributions up to 15 cm in the estuary, 5 cm in the near-field plume and 1 cm in the far-field plume. The exact height will depend on the river discharge, wind conditions and the tides, which strongly affect the river plume, and thus also the sea surface height. During the summer of 2022, the discharge of the Rhine River was historically low. We investigate the consequences for the river plume, and its impact on the sea surface height. We find that river plumes can induce significant steric changes in sea-surface height, however these are often neglected. Climate change will affect the different drivers of sea level variability in our coastal zones and shelf seas, including river discharges. Understanding their impact is therefore crucial to assess changing sea levels.