Multi-temporal relative sea level rise scenarios up to 2150 along the Italian coastal plains: new insights from the GAIA Project

The coastal plains of the Italian peninsula and its main islands are highly exposed to the ongoing sea-level rise triggered by global warming and often accelerated by land subsidence. In the frame of the GAIA Project, funded by the Italian Ministry of University and Research, here we focus on the current and expected relative sea level trend at 2030-2050-2100 and 2150 for 39 main coastal plains which are affected by spatially variable rates of Vertical Land Movements (VLM). To estimate the current VLM rates we have used geodetic data from about 27 years of continuous GNSS observations at selected stations located within 5 km from the coast and InSAR data from the Copernicus European Ground Motion Service (https://egms.land.copernicus.eu/). The latter were integrated with additional InSAR data sets to extend the data time series to the last decade. We provide revised sea level rise projections for the entire Italian region by including the estimated VLM in the SL projections released by the IPCC in the AR6 Report for different Shared Socio-economic Pathways and global warming levels (www.ipcc.ch). To reinforce the analysis and the interpretations, we also considered the sea level data recorded at the tide gauge stations belonging to the PSMSL (https://psmsl.org) and ISPRA (https://www.mareografico.it/) networks. Results show the current IPCC projections are often underestimated and not representative of the expected future sea levels since they neglect the effect of VLM due to tectonics and local factors. Finally, we show detailed maps of the expected flooding scenarios for 39 main coastal plains of the Italian region, projected on high resolution DEM obtained by the spatial analysis of LiDAR data available from the Italian Ministero dell’Ambiente e della Tutela del Territorio. The geoprocessing, that included the reanalysis of the vertical datum of the original LiDAR acquisition to project the scenarios on the mean sea level, highlighted that about 10.000 km² of the coasts are yet exposed to multiple coastal hazard. Enhanced impacts on the environment, human activities and coastal infrastructures, are expected, requiring adaptation measures to face the ongoing sea level rise.