## 1 Introduction  
Sea-level rise (SLR) is one of the major consequences of global warming, driving the melting of ice sheets and the thermal expansion of the oceans, increasing the vulnerability of coastal areas to flooding. Over the past two centuries, the global sea-level (GSL) has risen at faster rates than in the last two millennia [1; 2], with values from 1.7 mm/year in the late 20 th century up to 3.2 mm/year over the last decades [3; 4; 5; 6]. The latest report of Intergovernmental Panel on Climate Change (IPCC, Special Report on the Ocean and Cryosphere in a Changing Climate SROCC [7]) shows that in 2100, GSL projection has an upper limit of about 1.1 m higher than present sea-level, while about 400 million of people will be highly exposed to coastal hazard. SLR can be exacerbated by land subsidence from natural (i.e., tectonic and volcanic activity and sediment compaction) and anthropogenic causes (i.e., fluid withdrawal, dams building), accelerating the submersion process of low-elevated continental [8; 9; 10] and insular coasts [11; 12; 13]. Coastal flooding is likely to be the biggest socioeconomic impact of SLR in the 21 st century [14] exceeding the damage caused by earthquakes and volcanic eruptions. Recently, [PERSON] et al. [15] delineated the requirements for a scientific approach for future projections of shoreline changes, which should consider changes in the mean sea-level, storm surges, coastal erosion and other additional factors, with the aim of reducing uncertainty in coastal change estimates. Indeed, the rate of relative SLR (RSLR) can vary significantly due to other processes such as isostatic adjustments, ocean currents, seismic and volcanic activity, besides the already cited natural and anthropogenic land subsidence. These phenomena are already affecting the global coasts and large coastal cities [16], including the Mediterranean [17] (www.savemedcoasts.eu and www.savemedcoasts2.eu, accessed on 4 February 2021 [18]). SLR, in conjunction with extreme storm surge events, caused dramatic flooding, such as in 1953 for the coast of Netherlands or more recently in New Jersey (2012, Hurricane Sandy), Louisiana (2015, Hurricane Katrina), Florida (2016, Hurricane Matthew), Louisiana and Texas (2017, Hurricane Harvey) and in the Mediterranean Sea in 2019 and 2020 [19; 20; 21]. Because relative sea-level change along the coast is given by the sum of eustictic, thermo-steric, isostatic, sediment compaction and tectonic factors [22; 23], the projection of the future coastline positions in specific zones require to consider in the analysis: (i) the local rate and trend of sea-level change and (ii) the rate of vertical land movements (VLM), including tectonic and isostatic contributions and anthropogenic influence. The first are provided by the latest IPCC reports [7; 24] and can be downscaled for specific regions, while the second are provided by geodetic data, such as sparsely GNSS stations and InSAR observations [25]. The latter can much improve the spatial coverage and resolution to characterize and detail land subsidence, whereas GNSS provide precise measurements in well-defined, ground-based, reference frame, to which InSAR measurements can be referred. Assuming that VLM rates estimated from geodetic data will remain constant for the next few decades in a specific coastal zone, i.e., in absence of any relevant tectonic event, relative sea-level rise projections and flooding scenarios for the coming years (2100) can be reasonably realized. Scenarios can be mapped on high resolution 3D topography of the investigated zones, supporting the analysis of the flooding extension and the assessment of the coastal impacts. Digital Elevation Models (DEM) extracted by LiDAR data are the most suitable tools to realize realistic scenarios. Here, we report on accurate observations of VLM along the coast of southern Sicily between the city of Catania and the village of Marzamemi, from a combination of GNSS, InSAR and tide gauge observations at an unprecedented resolution and accuracy (Figures 1 and 2).