Assessing the Exposure of Coastal Cultural Heritage Sites to Sea Level Rise Phenomena in the EU Mediterranean Countries using open access data

The Mediterranean Sea has a long record of cultural heritage sites located near its coast, reflecting each nation’s historical continuum and identity. These monuments also attract tourism and provide financial benefits to local communities. However, they are subject to structural damage and decay exacerbated by climate-change-related phenomena including extreme weather events, sea-level rise, etc. Sea Level Rise (SLR) is a major threat to coastal heritage sites as it can  lead to extensive inundation and soil erosion. SLR projections are constructed by studying representative pathway scenarios (RCP), which try to deliver possible alternatives about the future atmospheric composition.  SLR has escalated from an average of 1. 2 mm/year before 1990 to 3 mm/year between 1993 and 2010, with projections indicating a rise of 1–2 meters by 2100 across different scenarios.

The ongoing Triquetra Project, funded by the European Union, aims to design a toolbox for assessing and mitigating climate-related risks and natural hazards, expected to affect Heritage Sites. A methodology has been developed to evaluate future exposure of coastal heritage sites SLR in EU Mediterranean Countries. This workflow uses open-access data to produce SLR projection maps for 2050 and 2100 based on the IPCC (2019) report for RCP 2.6, 4.5, and 8.5. Four main sources of data were used: a hybrid coastline vector file combining national fine-scale datasets with the European Environment’s Agency (EEA) coastline file, FABDEM as the primary source of elevation information,  the European Ground Motion Vertical Service’s (EGMS) L3 product which measures vertical ground movements using Synthetic Aperture Radar Interferometry (InSAR) data from the Sentinel-1 mission, and, finally, NASA’s Sea Level Projection Tool which provides information on all RCP scenarios. Coastal Heritage Sites and Assets were identified using OpenStreetMap and UNESCO’s Word Heritage Site point layer.

The pre-processing stage of the algorithm involves the projection of all datasets into a common coordinate reference system, the clipping of the data into the area of interest (AOI), defined as a 2km buffer zone from the coastline, and the conversion of EGMS and NASA’s SLR data units to meters. The algorithm proceeds with raster calculations to determine the AOI’s elevation for the target years 2050 and 2100 under different RCP scenarios by adding the elevation values to the EGMS data and subtracting NASA’s SLR projected values. Raster calculations and Boolean algebra are performed to identify sub-areas affected by these scenarios. Finally, spatial queries are conducted to find coastal heritage sites at risk from Sea Level Rise, organized by monument type and country for vulnerability assessment.

The results demonstrate that Greece, France, and Italy are expected to be more affected by SLR phenomena due to their extensive coastline and unique geomorphology, with the impact being more severe on Greece and Italy between 2050 and 2100. Finally, more than 240 heritage sites appear to be at risk primarily on the Greek and Italian coast, including UNESCO sites like Delos, the Medieval City of Rhodes, et al.