The CoastLine project, created by the Laboratório de Arqueologia e Conservação do Património Subaquático [Laboratory of Archaeology and Conservation of Underwater Heritage] at the Polytechnic Institute of Tomar, aims to recognize archaeological sites located in areas subjected to climate risks along the Portuguese coastline, as well as contribute to mitigating the impact of climate change on this heritage. By highlighting the issue and analyzing these sites, the project seeks to establish action priorities and strategies for more informed decision-making by competent authorities and the community, for the future safeguarding of these sites.

Based on these premises, a set of comprehensive analyses was carried out on the existing sites, considering their chronologies, the nature of the remains, proximity to or overlap with areas likely to be affected by environmental risks, the type of predicted impact, among other relevant factors.

Based on these analyses, a first classification proposal was developed, taking into account the incidence of impacts, in order to establish intervention priorities and raise awareness of the vulnerability of these sites, as well as encourage the implementation of more effective protection measures.

One of the direct measures proposed is the inclusion of sites marked by the PC-IP as requiring emergency intervention, so that they can be addressed with concrete solutions. This could involve the development of appropriate study and protection projects in collaboration with local authorities to safeguard these sites.

It is also necessary to vigorously begin integrating this issue into national strategies for Integrated Coastal Zone Management. While recent texts emited are sensitive to sustainable development and monitoring and identification of risk areas, aligning with other strategies such as the National Territorial Planning Policy Program, the National Sustainable Development Strategy, Tourism, and others, they do not reflect direct strategies for the safeguarding of cultural heritage.

 

General context and climate change

The perception of abrupt climate changes that we are facing is widely accepted by the scientific community and has been the subject of significant debate. The latest report from the Intergovernmental Panel on Climate Change (IPCC), underscores beyond doubt that human influence "has warmed the atmosphere, ocean, and land" (IPCC, 2023, p. 5). The report also highlights the growing severity of erosion and sea level rise. According to it, the global mean sea level increased by 0.20 [0.15 to 0.25] meters between 1901 and 2018, at a rate of 1.3mm/year from 1901 to 1971, and 1.9mm/year from 1971 to 2006, drastically increasing to 3.7mm/year in recent years. Furthermore, the report addresses other climate impacts on the oceans, such as the increase of extreme weather events or "increased ocean acidification (virtually certain) and deoxygenation (high confidence)" (IPCC, 2023, p. 13). And, as it has already been pointed out by various specialists and researchers (Lehner and Peacock, 1988; Lighfoot, 1992; Culley and Meade, 2004; Monteiro, 2015, Rosado, 2019) these changes in the chemical parameters of water, for instance, have significant consequences for the preservation of submerged archaeological remains, both organic and inorganic.

In recent decades, several studies have highlighted the relevance of these parameters in Portugal, where a systematic degradation of the coastline is evident (Dias, 1990). The coast, predominantly sandy, is even more vulnerable to the various threats arising from both natural factors, such as highly energetic waves, and anthropogenic actions (Barros, 2023; Rosa-Santos, 2009). The sea level, excluding the potential acceleration of the phenomenon, was estimated in 1992 to rise by 14 to 57 cm by 2100 in Portugal (CNADS, 2001). This phenomenon exacerbates the erosion effect, which is already significantly impacted by human activities such as the construction of dams and sand extraction (Rosa Santos, 2009). Sediment sources from rivers have been diminishing over the years, and it has been established that human actions are responsible for an 80% reduction in sand transport from rivers to the coastal sea (Dias, 1990). Sustainability-oriented policies have been implemented in recent decades and have had a positive impact, although results are still far from the desired outcomes (Dias, 2014).

This brings us to our actual project as we still lack of a clear understanfing of the impact of climate change on the portuguese archeological sites, hindering effective action in the short, medium, and long terms for the preservation and safeguarding of Portuguese heritage

Previous Study

Basing the study on the climate data provided by the Agência Portuguesa do Ambiente (APA) [Portuguese Agency for the Environment] and the Patrimônio Cultural, Instituto Público (PCIP) [Cultural Heritage, Public Institute] database of heritage sites, we decided to cross-reference both sources in order to create a map of sites at risk due to climate change and an urgency chart for these sites. The goal being to assist in the management of these sites and minimize the associated risks.

A first map has been created, integrating data from the APA, over a 50 years span. For sandy coastlines, the following have been considered:

•     Coastal Erosion Safeguard Zones: These correspond to “areas potentially affected by coastal erosion and coastline retreat” over a 50-year time horizon, based on the extrapolation of observed evolutionary trends in the recent past.

•     Safeguard Zones for Coastal Flooding and Inundation: These correspond to “areas potentially affected by overtopping and coastal flooding” over a 50-year time horizon, “resulting from the combined effect of the mean sea level, astronomical tide elevation, meteorological over-elevation, and wave overtopping, including the rise in mean sea level in the context of climate change” (Id.).

For cliffed coastlines, the following data was considered:

•     Safeguard Zones for the Sea: These correspond to areas at the foot of the cliff, or other slopes in the coastal domain, that may be affected by debris resulting from mass movements along the slope.

•     Safeguard Zones for the Land: These correspond to areas adjacent to the cliff crest, or other slopes in the coastal domain, that are more likely to be affected by mass movements of various types and scales (Agência Portuguesa do Ambiente - SNIAmb, n.d.).

•     Potential Instability Areas: These correspond to any slopes (natural or artificial) “with potential instability and susceptibility to mass movements” (Id.), without being directly related to erosion caused by waves.

It is important to note that, due to a lack of climate information concerning the Algarve region, this study does not yet include this area of Portugal, even though it has been shown to be a sensitive region, especially due to intense construction along the coastline (Dias, 2014).

 

The archeological sites have been provided by the database of the PC-IP, and have been considered only the sites up to a hundred meters from the coastline.

It is important to note, some limiting characteristics of this database, namely:

a) The geographical point used as a reference for the location of archaeological sites represents only a small part of the total area (a single point). It is important to emphasize that human occupation sites often extend more broadly and are more dispersed (in area), potentially covering significantly larger zones that may go beyond the indicated location.

b) Some of the points identified as archaeological sites are located outside the areas initially defined as at risk. However, it is important to highlight that the dispersion of archaeological remains, typical of human settlements, may cover these areas. Therefore, these archaeological sites may not have been adequately considered in our analysis, being classified under lower risk categories or even excluded. Other situations occur in nearby areas, such as river mouths, which are subject to similar influences and were not analyzed (figure...).

c) Many of the references used for identifying the archaeological sites are several years old and may not have been recorded with precision using modern geospatial positioning mechanisms or tools.

Results and improvments

The map resulting from this cross-reference gives us alarming results. Indeed, it has been established that, considering a 100-meter stretch from the coastline, 486 archaeological sites have been included, of which 246 are at risk (50.6%). If we exclude sites located in the Algarve region, this brings us to 288 sites, with 246 at risk, which results in 85.4% of archaeological sites within 100 meters of the coastline being at risk over the next 50 years.

Using buffers, we established three levels of emergency:

•     High risk: Sites located directly or up to 100 meters from the risk zone delimited by the APA.

•     Medium risk: Sites up to 200 meters from the risk zone delimited by the APA.

•     Low risk: Sites up to 300 meters from the risk zone delimited by the APA.

 

In total, 214 of the 246 sites at risk are in the high-risk category, 22 in medium risk, and 10 in low risk. This significant discrepancy between the number of sites at high risk and those in other categories can be easily explained: the area considered by the LabACPS-IPT extends up to 100 meters from the coast. Therefore, the buffer zones included in the medium and low-risk categories (200 and 300 meters) can only extend laterally and cannot reach further inland. This analysis should be incorporated into the present project to allow for a more comprehensive evaluation of the data.

We can also note that the most affected periods are the Paleolithic, with 76 sites, and the Mesolithic, with 43 sites.

Finally, we highlight the overwhelming predominance of open-air sites, which underscores the urgency of the work that needs to be done and the significant loss of information that could occur if these locations are not urgently studied. This classification often reveals the absence of surveys and research on these sites, where remains were found on the surface—often following an extreme climatic event.

Conclusion

In conclusion, this initial study provides a general view of the situation, but it would require substantial improvement in order to become an effective support tool for sustainable management and safeguarding of Portugal's coastal heritage. It is in this context that we present this project. Several areas for improvement are identified:

•     Integration of more comprehensive climate change data, such as temperature rise, water acidity changes, and extreme weather events.

•     Precise verification of archaeological sites in the database.

•     Integration of the Algarve region.

•     Study and proposals for coastal management.

•     Consideration of various climate change scenarios, such as those used by the Cultural Heritage - Public Institut.