Michael G. Hart-Davis (DGFI-TUM, Germany); Christian Schwatke (DGFI-TUM, Germany); Tamlin M. Pavelsky (UNC, United States); Audrey H. Sawyer (OSU, United States); Richard D. Ray (NASA, United States); Denise Dettmering (DGFI-TUM, Germany); Florian Seitz (DGFI-TUM, Germany)

Coastal rivers are ecologically and economically vital transition zones between land and sea that are tidally influenced but fresh for much of their length. Tides in coastal rivers affect carbon and nitrogen cycling, sediment storage, and salinity, but the extent of tidal influence is generally unknown over most of the world's rivers. Tidal propagation is sensitive to local morphologic and hydrologic factors, and only a limited number of rivers have tide gauges globally. In the coastal and open ocean regions, tidal modelling efforts have successfully relied on conventional nadir altimetry for decades, but the method is less reliable in narrow river systems and inland water bodies due to land contamination of radar returns. Here, we use the recently launched SWOT satellite, which provides wide-swath elevation measurements at unprecedented scales, to produce a global empirical atlas of tidal influence in rivers for the first time. Tidal constituents are estimated based on the pixel cloud and RiverSP products and validated against in-situ river and tide gauges. Over 150,000 river kilometers are influenced by tides globally, and over 250 million people live near and depend on these coastal transition zones. Manmade and natural obstacles, such as dams, limit tidal propagation in an estimated 15% of all tidal rivers. These results demonstrate further opportunities to use wide-swath measurements to advance the understanding of tidal dynamics in these critical areas.