Impact of Continental Freshwater Runoff on Coastal Sea Level

Freshwater discharge to the coastal ocean is a fundamental component of the global water cycle. It can impact coastal sea level over a broad range of spatial and temporal scales. Here we review the status of the current knowledge based on observational and modeling approaches. The main limitation in studies of the influence of rivers on coastal sea level has been the lack of consolidated discharge databases. We first provide an inventory of the main data sources currently available. We then review the existing knowledge about the runoff forcing of coastal sea level, differentiating between the mass and steric height contributions. Both mechanisms are important for coastal sea level budget, although they act on different scales. The mass contribution is related to a global ocean response that is established on relatively short timescales through barotropic processes while the steric contribution is associated with more of a regional adjustment that takes place on longer timescales by means of baroclinic dynamics. While numerical models required to simulate the runoff impact on coastal sea level variability have been improving over the past decades, a similar evolution is awaited for observational techniques, both for in situ observation and for remote sensing.