Trends and inter-annual variability of altimetry-based coastal sea level in the Mediterranean Sea: Comparison with tide gauges and models

In the framework of the Coastal sea level project of the ESA Climate Change Initiative, a new coastal sea level product from the Jason-1, 2 and 3 missions over 2002–2018 has been made recently available. This product consists of along-track, high-resolution (20 Hz, i.e., ~350 m) sea level anomalies and coastal sea level trends derived from a complete reprocessing of the Jason altimetry data, including a retracking of the radar waveforms using the ALES (Adaptive Leading Edge Sub-waveform) retracker, in several coastal regions worldwide. In this study, we extend the assessment of this coastal sea level product in the Mediterranean Sea region by comparing with tide gauge data where available. We selected a set of 14 coastal sites where the distance between the Jason track at the coast is less than 30 km from a tide gauge for which the in-situ record at least partly covers the 2002-present time span. In a first part of this study, we compared the interannual variability and trends of the coastal sea level anomalies and of the tide gauge data. A good agreement is found between the altimetry-based sea level time series and the tide gauge data at interannual time scales. In terms of trends, the comparison also shows general good agreement within the respective uncertainties. In a second part of this study, we focus on the Senetosa site (south Corsica) where a significant altimetry-based sea level trend increase is observed in the last 3–4 km to the coast, and investigate which physical process could explain this trend behavior. We analyzed temperature and salinity data of the high-resolution (400 m) MARS3D model, available around Corsica over the January 2014 - December 2019 time span, and computed the steric sea level component and its trend along the Jason track. A clear steric sea level trend increase is found in the last 3–4 km to the coast. Although the MARS3D model does not provide outputs prior to 2014, we suggest that if the steric sea level trend increase found over 2014–2019 is a long-life time feature, it has the right amplitude to explain the altimetry-based coastal sea level trend increase observed at Senetosa.