As sea-level rise accelerates in Africa, African heritage sites are at risk

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Heritage sites are of great cultural, historical, economic, and social value^1,2. Global heritage is at risk from climate change hazards, such as wildfires and heatwaves, river floods, and heatwaves.^3,4,5. Multiple heritage sites, including World Heritage Sites of ‘Outstanding Universal Value’, are located in the low-lying coastal zone and therefore also face threats from coastal hazards due to rising sea levels. The sea level has been rising at a faster pace over the past three decades than in the 20th century.^6,7This is a process expected to pick up pace throughout the twenty-first Century^8,9. Along with changing weather patterns^10,11This is expected increase coastal flooding^12,13Coast erosion and coastal erosion¹⁴, exacerbating damage to coastal zone assets¹⁵. But, this is in contrast to other continents¹⁶, few studies have assessed climate change risks along the 300,000 km African coastline that spans 39 countries^3,4,17. Even sparser is information about the future of the continent’s cultural and natural heritage sites, many of which are found in the coastal zone.

We evaluate the vulnerability of African heritage sites (AHSs) to coastal flooding, erosion and dune destruction along the entire African coastline. We create the continent’s first digitized, geospatial database of 284 coastal African Heritage Sites. This database includes 71 cultural World Heritage Sites and 213 Natural World Heritage Sites. These sites are either currently being considered by the United Nations Educational, Scientific and Cultural Organizations (UNESCO) World Heritage Centre and Ramsar Convention on Wetlands of International Importance.^18,19,20,21. Our analysis focuses only on the coastal area that is exposed to 1-in-100-year coastal flooding and coastal erosion events. We estimate the area exposed at each site for the reference year 2010, as well as through 2021, under moderate (RCP (RCP) 4.5), and high (RCP (RCP (8.5) greenhouse gas emission scenarios. To determine the exposure to coastal flooding, we use a hydrodynamic model that is forced by extreme sea levels (ESLs), which combines sea level, waves tides and storm surges.²². We use the most recent shoreline changes projections to assess coastal erosion.¹⁴This information is combined with site-specific geological information that can limit shoreline erosion. Each site is assessed for erosion and flooding. We then calculate the total exposure as the sum of these two factors. We present the median value of exposed area and the very likely range. These values are expressed as 95th and 5th percentiles. We provide information about each AHS, and present our findings at country and regional levels. (See Methods for more details, including a detailed discussion on any limitations in a dedicated Section).

56 (20%) of 284 AHS are currently exposed at the moment to a 1-in 100-year coastal extreme. Thirty five of the 213 natural Heritage Sites (16%) and 21 out of the 71 Cultural Heritage Sites (30%) are currently exposed to 100-year coastal extreme events (Table 1), corresponding to 1,719 km²419 km²There are two types of cultural heritage areas and a natural area that is exposed. Each site has an average of 4.5% of its surface exposed. Fifty sites have <50% of their area exposed, 3 sites have >50% area exposed and 3 sites have >75% of their area exposed (Fig. 1).

Table 1 Coastal hazards exposure of cultural, natural and total AHS on the entire African coastline

**Fig. 1: Rising seas could expose more AHS coastal hazards to 2050.**

North Africa has the most exposed sites (23, out of a total number of 109; ExtendedDataFig. 1). 18 sites are exposed in West Africa, while 7 are in Southern Africa. East Africa and Small Island Developing States have 4, respectively. Tunisia contains the most heritage sites (34), 7 of which are exposed to a 100-year event, with 2 of them being highly exposed (>75% exposed area). Morocco and Senegal both have 7 sites, while Egypt has 4. Currently, there are no exposed sites in Central Africa.

The number of sites threatened by a 100-year coastal extreme event is projected to more than triple under moderate emissions, reaching 191 (very likely range: 191–196) by 2050 (Table 1). Based on the median estimates, North, West, Southern and SIDS are home to 68, 47 and 23, respectively. High emissions will increase the total number of exposed sites by 2050 to 198 (very likely range: 198–210), with 4 of the 7 additional sites (for the median estimate) found in North Africa and 3 distributed among the SIDS, Southern and West Africa.

The number of exposed sites for both high and moderate emission scenarios is stable in the second half century. However, there is a dramatic increase in the amount of exposure. Under RCP 4.5, the number of very highly exposed sites (that is, fraction of site’s exposed area >75%) increases fivefold from the present-day value, to reach 15 sites (14–20) by 2100; while under high emissions this estimate increases more than sixfold to 20 (17–30; Fig. 1). This is due to the fact that sea-level rise accelerates the growth of heritage areas (Fig. 2). The median additional area exposed to 2050 under high emissions is only about 25% of the baseline (1,719 km).² versus 2,171 km²The increase under moderate emissions is less than 2%. The median additional exposed area under moderate emissions increases by 9.5 times by the end century, reaching 16,638 km² (13,192–22,596; Table 1). The median area of high-emissions is 20,969 km² (15,168–28,051), about 12 times the baseline value (Table 1). These results highlight the benefits of reducing greenhouse gases emissions. Mitigation from high to moderate emissions would result a 21% decrease in the median exposed area and 25% less sites that would be exposed by the end. (Fig. 1).

**Fig. 2: Increased exposure of AHS to the 100-year coastal extreme, during the twenty first century**

On average, AHS will have 11.2% (9.4–14.2) and 13.7% (10.7–18.3) of their area exposed under moderate and high emissions, respectively (Table 1). These percentages are higher for natural sites than for cultural sites; for example, under high emissions, 15% (11.6–20.4) versus 9.7% (7.7–12.0), respectively, by the end of the century (Fig. 2c,d). Note that the mean exposed area is used as a proxy of the overall effect of coastal hazards on AHS, but it doesn’t imply that sites are interchangeable, nor that the characteristics of each site are homogeneous. Each site is unique and has outstanding value. It can be made up multiple components so that potential loss would not be equal across all sites. Projections indicate that at least 151 and 40 cultural sites will be subject to the 100-year event starting in 2050. This is regardless of the scenario (median value, Table). 1). Natural sites take up almost 10 times as much area as cultural sites, so most of the area exposed to them is also theirs. The exposed natural and cultural areas will equal 15,053 km under moderate emissions by the end the century² (11,906–20,545) and 1,585 km² (1,287–2,051), respectively (Table 1Fig. 2a,b). High emissions can lead to the same values rising to 18,930km² (13,652–25,545) and 2,039 km² (1,516–2,507), respectively.

Fig. 3Table 2). Under high emissions and for the worst-case scenario (that is, 95th percentile), four more countries are added to this list: Côte d’Ivoire, Cabo Verde, Sudan and Tanzania. Morocco and Tunisia have at least 13 more sites than currently (and at least 20 more depending on the scenario). Mozambique has the highest heritage area exposure (median value of 5,683 km).² under moderate mitigation; Fig. 3), followed by Senegal (>2,291 km²), Mauritania (>1,764 km²) and Kenya (>822 km²). Tanzania, Mozambique, Côte d’Ivoire, Benin, Togo and South Africa are countries that by the end of the century will have at least 100 times more exposed heritage area than at present. High emissions are expected to expose 51%, 30% 25%, 25%, 21%, and 20% respectively of Ghana, Sierra Leone and Mozambique. 4).

**Fig. 3: Country estimates for the extent of AHS that was affected by the 100 year coastal extreme event of the twenty-first century.**

Table 2 Country level projections for AHS exposure to the 100 year coastal extreme event by century’s end, under moderate (RCP4.5), and high emissions (RCP8.5).

**Fig. 4: Country estimates of how much of AHS was affected by the 100-year-long coastal extreme event in the twenty-first century.**

SIDS heritage sites, in particular, are at high risk. Curral Velho (1.575, Ramsar Site in Cabo Verde), for example, is an important wetland which will be vulnerable to coastal hazards by 2050. Under high emissions and by the end of the century, 44% of the site’s total area will be exposed. Aldabra Atoll (1,887), the world’s second-largest coral atoll, and Kunta Kinteh Island (The Gambia) could both see up to 17% and 46% area exposed by 2100 under high emissions, respectively.

Notable increases of percentage site exposure are also projected for some archaeological and cultural sites, such as the North Sinai Archaeological Sites Zone (189; 91%; RCP 8.5, 2100), Agglomération Aného-Glidji (1,505; 37%; RCP 8.5, 2100), the ancient Punic and Roman trading post, Tipasa (193; 11%; RCP 8.5, 2100), the archaeological site, Sabratha (184; 7.7%; RCP 8.5, 2100) and the archaeological site, Carthage (37; 5.9%; RCP 8.5, 2100). Qaitbay Citadel, the historic site of the Lighthouse of Alexandria (1.822) and one of the Seven Wonders of the Ancient World, is not included.²³It is expected to be exposed to minimal due to existing protections. However, it has already been subject to severe flooding in 2019 which led to the construction coastal defenses.²⁴.

Chat Tboul (1.044) and Parc Nat National du Diawling (666) in Mauritania, are two examples of sites that have been subject to extreme flood events despite efforts made to ecologically restore floodplains^25,26. The vulnerability of the socio-ecological systems of the Densu River Basin might be increased by the predicted total flooding at the Densu Delta Ramsar Site (564) by 2100 in both emission scenarios. This compares with a current value of only 47%.²⁷. Due to coastal erosion, a large portion of the remnants of the Guinean coast forests have already disappeared.^28,29. Parc National du Diawling (666): Future flooding and erosion could affect the entire site compared to a baseline that only exposed 45%. Such a substantial increase may affect the ecological equilibrium of the site’s ecosystem.

Africa is home to some of the most diverse cultural and bio-cultural heritage in the world, internationally recognized for its uniqueness and ‘Outstanding Universal Value’³⁰. Heritage sites have continuously served as ‘living’ heritage³¹ and therefore are deeply interwoven with the people’s identity and tradition, are essential for social wellbeing, safeguarding traditional knowledge and livelihoods, and constituting a prerequisite for sustainable development³². We found that 1 out 5 AHS in coastal areas are already at risk of a 1-in 100-year ESL event. This number is expected to nearly quadruple by end of century.

Flooding is more damaging to heritage than erosion. However, the impact mechanism of both hazards is different so their relative importance will vary depending on the location. Inundation would have a greater effect than erosion, which is dependent on the interaction between the flood depth, flow velocity, and the element inundated. Cultural sites, which are usually archaeological or built heritage, will be affected both by erosion and flooding. Bio-cultural areas and natural areas will be more resilient to episodic flooding. A partially flooded, eroded area of natural land may be able to accommodate these disturbances and maintain ecological equilibrium. It might migrate landwards, or shrink as a result of coastal development.

It is becoming increasingly important to know how much heritage sites can lose to flooding or erosion while still maintaining their value (for example, cultural and ecological, Indigenous, and economic). This question requires site-specific studies. The ability of natural coastal systems, such as those that are prone to salinity changes, to adapt to and absorb other external shocks is another question.¹⁷.

Anthropogenic modification of coastal processes will also affect natural systems’ responses to shoreline change. In West Africa, for instance, the construction dams on Volta River in the Bight, together with lower rainfall, led to a decrease sediments on the coast. This increased the likelihood of coastal flooding and erosion.³³. Many sandy beaches on the continent are protected by ecological elements such as coral reefs and seagrass.^34,35,36. However, coral reefs’ fate depends on future heatwaves in the ocean.³⁷Ocean acidification trends³⁸—both of which are expected to increase all around the continent—while mangroves are also threatened by rising seas. If rising seas exceed the rate of forest movement, then five species of mangrove could be extinct locally in Ghana.³⁹. These effects are also accelerated in Central Africa (Cameroon), as well as other regions, by mangrove logging as well as anthropization⁴⁰. The eastern African coast is considered a region with high diversity of seagrasses.⁴¹, is subject to frequent anthropogenic disturbance, resulting in the loss of about 21% of Kenya’s seagrass cover between 1986 and 2016⁴². These transitions could have additional indirect effects and weaken the natural coastal protection, further increasing flood risk. This could have significant social consequences.⁴³.

Our findings assist in prioritizing sites at high risk and highlight the need to take immediate protective action for AHS. This requires local-scale assessments of vulnerability as well as adaptation options. Relocation or managed retreat might not be an option for many cultural or natural sites due to their intrinsic values and potential impacts on local community.³. If they are technically and financially feasible, coastal protection may be possible through the construction of breakwaters and groins. Protections to Qaitbay Citadel (1.822) in Egypt have been strengthened recently.⁴⁴. However, such ‘hard’ protection strategies need to consider future sea levels and are known to distort the site’s natural ecological and morphological equilibrium⁴⁵. Hybrid protections that include ecological infrastructure such as rock sills and saltmarshes, marinegrasses, or restored mangroves may be more effective.^17,45. Improved monitoring and evaluation of local and Indigenous governance and larger land management actions such as expanded buffer zones can provide additional enabling conditions for site protection to address existing vulnerabilities.^2,46,47.

As climate risk to heritage increases, there is potential for these exposure finding to raise public concern. This could mobilize rapid and ambitious greenhouse gases mitigation to reduce overall risk as well as potential loss and damage.³. Future research will need to quantify climate risk to heritage in a more comprehensive manner, including risks to Africa’s inland culture. It is also necessary to have a better understanding of the potential impacts of compound climate extremes and other climate hazards on heritage. A better understanding of heritage risks and climate change responses is also needed.⁴⁸Migration, managed retreat, ecosystem-based adaption and relocation are all examples.

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