Sea level trends and variability in the Adriatic Sea and around Venice

A preliminary analysis of sea level (SL) changes around Venice from three tide gauges (TGs) (one off-shore: AAPTF, one at the coast: DSL, and one inside the lagoon: PS) to characterize the variability during 1993-2015 and relative SL trends, is provided. As no global positioning system (GPS) data covering the same period was available to the authors for the three tide gauges, the analysis is restricted to changes relative to the land. Monthly SL means from the European Space Agency (ESA) Sea Level Climate Change Initiative (CCI) altimeter-derived product are also used. A comparison between the monthly mean time series of CCI and AAPTF has been performed using the nearest CCI grid point to the location of AAPTF: the centered Root Mean Square Difference (cRMSD: the root mean square difference of the two series with the respective means removed) resulted 6.33 cm, while the Pearson's linear correlation reached 0.75. Much higher agreement was found, as expected, between the monthly mean records of AAPTF and PS TGs: the cRMSD was 1.03 cm, and the linear correlation 0.99. We obtained 6.65 mm year1 at AAPTF over the Satellite Altimetry (SA) era (1993-2015). A smaller trend has been found here from altimetry (4.25 mm year1). The differences might be explained in terms of Vertical Land Motion (VLM) which was not accounted for in the TGs time series, to the different processing of TGs and altimeter data (in the altimeter signal the Dynamic Atmospheric Correction is removed), and/or uncertainties in this area due to the current CCI product that is based on open ocean altimetry. In general, the altimetry trends derived from CCI are spatially higher in the Adriatic Sea than Global Mean Sea Level (GMSL) in most of the region, with greater values than average in Venice. Reprocessing of along-track altimeter data sets with consistent coastal processing for all missions is expected to enhance SL accuracy and with a better refining of raw trends. The SA era is too short to delineate or discuss an affordable climatology, as decadal SL variations cannot be accounted for by such a short time series, nonetheless the rates calculated in this study are fruitfully compared each other and with those derived by SA.