Rivers and Tides: a first global analysis from the SWOT satellite mission

The land-sea interaction of water is a complex system crucial for a wide range of biogeochemical phenomena, ranging from compound flooding to feeding patterns to pollution distribution. Ocean tides are a natural phenomenon that plays a significant role in the dynamics of water within the land-ocean continuum. Observing the propagation of ocean tides into inland water systems on a global scale is challenging. Although in-situ gauges are regularly deployed and maintained, the spatial distribution both in individual river systems and across all global rivers is insufficient to study the tidal influence on a global scale. In the coastal and open ocean regions, tidal modelling efforts have successfully relied on conventional nadir altimetry for decades, which has resulted in the refinement of tidal predictions throughout the global oceans. However, producing reliable estimations within river systems and inland water bodies is particularly challenging due to land contamination of radar returns, especially in rivers with smaller river widths. The recently launched SWOT satellite provides wide-swath measurements at unprecedented scales, which are aimed at producing water level measurements across all global water bodies. These data have already proved to be particularly useful for the study of ocean tides at fine spatial scales within complex coastal regions, with early results indicating clear avenues for advancement in tidal research, including in inland waters (Hart-Davis et al. 2024). 

This presentation introduces the estimation of tides within river systems based on the SWOT hydrological products. Tidal constituents are estimated based on the pixel cloud and RiverSP products and validated against in-situ river and tide gauges. Based on these findings, a global atlas of tidal influence is presented for the first time, describing the extent to which tides propagate or influence river systems. These findings, which are based on a combination of the Cal/Val and science orbit of SWOT, demonstrate a clear added value of the SWOT data processing in allowing for the advancing of tidal knowledge in regions typically challenging to resolve. 

Hart‐Davis, M.G., Andersen, O.B., Ray, R.D., Zaron, E.D., Schwatke, C., Arildsen, R.L., Dettmering, D. and Nielsen, K., 2024. Tides in complex coastal regions: Early case studies from wide‐swath SWOT measurements. Geophysical Research Letters, 51(20), p.e2024GL109983.