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Abstract

Along the coast of the Netherlands, ocean dynamic sea level (ODSL) is one of the most important contributors to sea-level rise in the 21^st century. The ODSL output from the latest coupled model intercomparison projects (CMIP5 and CMIP6) is used for these projections. These CMIP models overwhelmingly use ocean models with a spatial resolution of 1° and a vertical z-level coordinate. Using these CMIP models for projections does not provide a connection between observations and projections. This study aims to improve on that. To do so, we use a configuration of the Regional Ocean Modelling System (ROMS) for the North Sea with a resolution of 0.25° to downscale the spatial resolution of CMIP6 models and interpolate the vertical coordinate to topography-following sigma levels. First, we use ROMS to reconstruct the ODSL for the observational period. The regional model is forced using a dataset constructed from ERA-interim and ERA-5 atmospheric surface data and multiple ocean reanalysis datasets. It is not straightforward to compare the ODSL from different ocean reanalyses, as some datasets assimilate satellite altimetry data, whereas others do not. Therefore, the ODSL from the reanalysis datasets that assimilate altimetry data are corrected for land ice and terrestrial water storage contributions. We use ROMS to obtain new projections of ODSL that seamlessly connect to the estimate of ODSL from ocean reanalysis data by extending the observational forcing datasets using anomalies of projections from CMIP6 variables for forcing scenarios 2.6, 4.5 and 8.5.