Before the flood

'If no measures are taken, World Heritage Sites will possibly be destroyed or even disappear due to rising sea levels.’

The effects of the changing global climate can already be seen in archaeology. Glaciers and permafrost, for instance, are melting at faster rates, exposing artefacts once preserved by the ice. Rising sea levels, too, bring with them an increased risk of floods and coastal erosion at seaside sites.

Around the Mediterranean, there are many sites within easy reach of the sea, which aids travel and trade, and provides food and other resources. A study published in Nature Communications in 2018 examined the risks at the 49 Mediterranean UNESCO World Heritage Sites in low-lying coastal areas, among them the Greek island of Delos, Venice, and Diocletian’s Palace in Split. Most, the study found, are at risk from hazards from the sea.

UNESCO World Heritage Sites in low-lying coastal areas of the Mediterranean such as Venice (above) and Tyre (below) are at risk from flooding and/or erosion. The levels of risk are likely to increase as sea-levels rise.

After producing a spatial database of the World Heritage Sites in these coastal areas, researchers led by Lena Reimann from Kiel University combined this data with simulations on the coastal floodplain of storm surge events under different sea-level rise scenarios, also used by the Intergovernmental Panel on Climate Change (IPCC), until 2100. The same sea-level rise scenarios were also used to project the risk of coastal erosion as the waters come closer to the sites. The study found that 37 of the 49 World Heritage Sites are already at risk from floods, and 42 from erosion, although the level of risk varies from site to site, with Venice and Ravenna particularly at risk from flooding, and Samos and Tyre from erosion. By the year 2100, this flooding risk may increase by up to 50% and erosion by 13% across the region, with the changes more pronounced at certain sites.

What can sites do to reduce the effects of these hazards? Management plans for World Heritage Sites vary, but few consider the impact of sea-level rise, the study points out, and although climate change has been recognised as a danger to sites, there has been little research on this threat. Reimann said, ‘The results of our study illustrate that adaptation is urgently needed at World Heritage Sites to ensure that their Outstanding Universal Value is not threatened by sea-level rise. However, adequate adaptation measures for different World Heritage Sites will depend on the location, the characteristics, and the type of the site. Further (national- and local-scale) studies need to explore measures suited for each site. Conventional measures (e.g. dykes) are likely to be less suitable as these may compromise the aesthetic value of the site. I would expect that different disciplines need to contribute for designing non-conventional, innovative solutions, e.g. architecture, arts, and engineering.’

The increased risks can also be limited, to a certain extent, by reducing climate change, and in turn the potential sea-level rise. Reimann added, ‘If rigorous climate change mitigation is pursued as planned under the Paris Agreement, future increases in flood risk and erosion risk could be kept to a minimum. Even with a temperature increase of 1.5°C, the impacts of climate change will be tremendous, as shown in the IPCC Special Report on Global Warming of 1.5°C. So it is important to keep the increase in flood risk and erosion risk at World Heritage Sites as low as possible to ensure that we can protect our common heritage from the impacts of sea-level rise, at least to a large degree. If the outstanding value of the affected sites is lost, we will not be able to simply restore it.’ 

‘The iconic nature of World Heritage Sites can be used to emphasise the severity of their loss in order to raise awareness of policymakers and heritage managers and to promote climate change mitigation. This requires considerable effort, willingness and, first of all, awareness, which we aim to raise with this study. Additional future research is needed at different spatial scales to further characterise the risks that sea-level rise poses to our common heritage. If no measures are taken, World Heritage Sites will possibly be destroyed or even disappear due to rising sea levels.’

Further reading
Lena Reimann et al (2018) ‘Mediterranean UNESCO World Heritage at risk from coastal flooding and erosion due to sea-level rise’, Nature Communications 9, 4161 (https://doi.org/10.1038/s41467-018-06645-9).

Images: Martin Falbisoner, Wikimedia Commons [CC BY-SA 4.0] / Heretiq, Wikimedia Commons [CC BY-SA 2.5].