## 4 Results and Discussion  
Since the last decade, new studies primarily based on IPCC projections, started to provide future sea-level rise assessments along the global coasts, generally without considering the contribution of VLM ([PERSON] et al., 2010; [PERSON] et al., 2011). [PERSON] et al. (2010), [PERSON] et al. (2011); [PERSON] et al. (2011) and [PERSON] et al. (2011), constrained the spatially variable VLMs based on long-term geological data (mainly the elevation of the marine terraces of the MIS 5.5) to obtain RSLR scenarios for 2100 along low-lying coasts of the Italian peninsula. Recently, instrumental data from GNSS networks, InSAR observations and tide gauges have been considered in these projections for the realization of inundation hazard maps in several areas such as the coasts of California ([PERSON] et al., 2011) and specific coasts of Italy ([PERSON] et al., 2010; [PERSON] et al., 2011; Sicilia et al., 2011; Sicilia et al., 2011; Sicilia et al., 2011; Sicilia et al., 2011), assuming that VLM rates measured by geodetic instruments will remain constant in the coming decades in a specific coastal zone. Figure 6: Multi-temporal shoreline changes observed along at the mouth of Ciane river in the time span 16 September 2002–20 August 2019. In 2019, the southern sector of the beach has been affected by a foredune breaching. In 17 years, the coast retreated up to 70 m due to the effect of RSLR with a loss of surface of 0.07 km\({}^{2}\). Our results underline the importance of a multidisciplinary approach for the RSLR assessment to predict the future submersion of investigated coasts. The multi-temporal maps of the expected submersion for 2050 and 2100 have been obtained through an integrated analysis of SLR projections, VLMs and the detailed representation of the shoreline migrations on high resolution DEMs. The conceptual approach is based on the worst conditions for a mobile coastal system, in which the coastal resilience is not sufficient to contrast the sea-level rise. Such conditions are particularly evident in the coastal areas characterized by low sediment supply and retreatment of the river mouths (for example the Simeto river mouth, Figure 7). Moreover, strong subsidence could act locally, preventing the dynamical response of the coastal system. A negative contribution that affects the Southeastern Sicily coasts is due to the anthropogenic factors [111], which determined the decrease of sediment supply and fluid withdrawal. Obviously, in the attempt to propose a future scenario, it is necessary to make some hypotheses and, in our case, it has been assumed that the ground deformation is linear over time. This velocity rate is considered to be constant and equal to that obtained from 4 years of monitoring with SAR data. This assumption is considered valid as the GNSS data also confirm that over a much longer temporal period (more than 20 years). Furthermore, we showed how the vertical displacement retrieved by the two remote sensing techniques, e.g., InSAR and GNSS, are comparable as well confirming our starting assumption. Finally, considering the tectonic regime of the area, we can state that most of the observed vertical velocities recorded at the GNSS stations show tectonic stability, with the exception in the north of Catania, near the Etna volcano. On the other hand, the low rate of land subsidence recorded south of Catania, fit the GIA values for this region, which have been estimated between \(-0.5\) and \(-1\) mm/year [29]. Results highlight the contribution of sea-level rise to the shoreline retreat at a level lower than 35% (Figure 8). Below are reported the estimated shoreline changes for a set of coastal zones:  
_Catania coastal plain._ A variable shoreline change was estimated between 6.34 and 3.23 m/year (with a linear regression of 4.78 \(\pm\) 2 m/year). In the proximity of the Simeto, Gurnazza and San Leonardo river mouths a fast shoreline retreat, up to 10 m/year, was observed [111].