Special Report
Managed Retreat: Preparing Coastal Cities for Sea Level Rise
By 2100, sea levels could rise by more than a meter without drastic reductions in our greenhouse gas emissions, according to the latest IPCC report. This global average encompasses diverse local realities, and many uncertainties remain regarding the exact pace and magnitude of the phenomenon. While coastal cities attract a growing population and concentrate numerous activities, they are confronted with coastal erosion, marine submersions, loss of land, flooding, erosion, salinisation of soils, and the degradation of ecosystems. One thing is certain: they must adapt immediately and sustainably.
Several adaptation solutions are possible and can be combined in space and time to meet local needs: hard and soft protections, accommodation, nature-based solutions, or even relocation. Also known as managed retreat, this strategy, although complex to implement, will sometimes be inevitable. Unlike emergency management, managed retreat is defined as a planned effort to permanently relocate people, assets, and infrastructure away from areas at risk.
Because of its complexity, managed retreat is a topic which attracts much debate and resistance among both the populations concerned and policy and decision makers. To better anticipate, design, and implement this adaptation strategy, it is essential to bring about changes in narratives and to work towards a shared understanding of the issues and the methodologies that can accompany its deployment.
With this in mind, the Ocean & Climate Platform, as part of the Sea’ties project, publishes a special report on “Managed Retreat: Preparing Coastal Cities for Sea Level Rise“. Intended for policymakers, and key stakeholders involved in the adaptation of coastlines, this special report proposes an in-depth analysis of managed retreat and methods for its implementation, illustrated and incarnated by the voices of experts and from the field.
The five testimonies below, extracted from the special report, show that while the path of managed retreat is complex, it is not impossible and can even be an opportunity to profoundly and sustainably transform cities for the benefit of societies and biodiversity.
Click on the cover to dive into the Special Report “Managed Retreat: Preparing Coastal Cities for Sea Level Rise”
Voices from the field:
Managed retreat across the world
A proactive response to safeguard
Managed retreat should not be seen as a last-resort solution or a failure of adaptation; rather, it is a proactive adaptation strategy that must be anticipated in order to safeguard vulnerable populations. Given the significant economic, social, and environmental costs of maintaining infrastructure and populations in high-risk areas, managed retreat can often emerge as a more effective and sustainable solution over time. It is already in regions like Saint-Louis in Senegal: a valuable case study in the importance of forward planning. By anticipating the need for managed retreat, we can avoid the unintended and often maladaptive consequences of emergency relocations. Al Hassane Loum, head of the Saint-Louis Municipal Development Agency, highlights that relocation is not merely a process of displacement; it is an ongoing, dynamic project that evolves in close collaboration with local communities, ensuring that the transition is both sustainable and community-centered.
Saint Louis, Senegal: sustainably rehousing after an emergency
Overlooking the Atlantic Ocean, the Langue de Barbarie, a thirty-kilometre sandy peninsula protecting part of the city of Saint Louis, is particularly exposed to climate risks, erosion and flooding. In 2017, while a major five-year project was being prepared by the World Bank to implement an adaptation and resilience strategy for the city, a devastating tidal wave disrupted everything. The situation quickly escalated into an emergency, endangering an entire neighbourhood of fishers. Several dwellings were completely destroyed, displacing close to 1,500 people who were forced to take shelter in makeshift tents under precarious conditions. Those remaining had to be convinced to evacuate quickly. A 4.5-kilometre-long and 20-metre-wide strip was delimited where houses would be demolished, making way for defensive structures to halt the encroaching sea.
A traumatic event for the families who, not only had to cope with the loss of their former way of life, but also had to trust the promises being made to rehouse them. “We undertook a study in an attempt to measure acceptability,” remembers Al Hassane Loum, head of the Saint Louis development agency and researcher at Gaston Berger University in Saint Louis. “At the peak of the emergency, 90% of the families agreed to be rehoused. They had no choice in the matter. In that case, we talk about involuntary rehousing.”
“We quickly realised that we had to provide housing that was an improvement over what had been lost,” explains the researcher. “Architects presented designs that were refined until acceptable.” But adjustments had to be made. “The basic principle for rehousing was ‘one house built for every house destroyed’. But due to the very high density of the original site, we increased the number of homes to be constructed. Particular care was given to the living environment. For instance, former neighbours were allowed to reunite if they wished, and essential amenities like schools, a healthcare centre, roads, and areas for gardening were included.”
Luckily for Saint Louis, the city has a local development agency dedicated to address social engineering issues, and a regional development agency which guides and coordinates actions between local councils. “These two agencies are responsible for finding the right channels (meetings, films, etc.) for communicating with the population of Saint Louis and the other neighbouring municipalities,” indicates Al Hassane Loum. “They are highly skilled.”
[Relocations] can only be done step by step, very progressively.
“In the meantime, before the dwellings are ready, a temporary dyke was built as part of the project to protect Saint Louis. This led certain inhabitants to believe their former homes were now safe, and they no longer needed to move out.” Explaining is a never-ending process.
The next stage involves planning for the year 2050, even 2100, when the entire city of Saint Louis could be at risk. “Once again, if we want to warn and convince the populations, we need to possess all the information. This includes scientific data, simulations and models so that we can explain and gain the populations’ support. Such work can only be done step by step, very progressively. It’s far from being complete.”🟡
An opportunity to collectively redesign coastal cities
Managed retreat goes beyond simply protecting assets and populations; it is a transformative territorial project capable of driving social, economic, institutional, and environmental change. It is not about merely relocating existing coastal infrastructure inland; instead, it offers an opportunity to collectively design a more desirable future for coastal cities. This approach often sparks broader societal and environmental discussions, making it a catalyst for reimagining the future of coastal cities. The examples of Petit-Bourg in Guadeloupe and Le Prêcheur in Martinique highlight the critical importance of engaging residents and all relevant stakeholders. Their active involvement is essential for gaining acceptance of these local transformations, which have the potential to disrupt established lifestyles and reshape both individual and collective histories.
In Guadeloupe and Martinique, public consultations precede relocations
On the islands of Guadeloupe and Martinique, shoreline retreat and collapsing cliffs are now well-known risks. Two localities are particularly affected: Petit Bourg in Guadeloupe and Le Prêcheur in Martinique. Both islands have instigated pilot projects to rehouse populations and thus ensure their safety.
The projects are inevitably different but they share at least one similarity: the idea that involving as many of the inhabitants as possible through early anticipation and regular explanations and dialogue is essential.
Studies in Petit Bourg have shown that, due to prohibitive costs, demolishing rather than consolidating the cliff was the preferred option to safeguard housing. Field assessments determined that around eighty houses, home to forty families, were situated in areas posing a serious risk to human life.
“The co-designing period was vital,” said Virginie Bonot, director of Urban Planning and Development for Petit-Bourg. “During the initial phase we organised public meetings which brought together the entire project team, including representatives and technicians from the town council, the State and the 50 Pas Géométriques Agency, as well as engineers from the French Geological Services (BRGM). Additionally, two representatives from the social housing development body, the MOUS, played an essential role in leading individual meetings with families during the second phase of consultation. These two people from the MOUS established a bridge between the project team and the families to facilitate document collection and keep families informed about meetings and project progress. All inhabitants could contact them directly by telephone. We were lucky to have these people right from the very beginning of the operation, for almost five years!”
Such close contact with the population allowed the team to defuse any disputes, to reassure whenever necessary, and to build trust.
We couldn’t pursue this project without involving the population right from the start
Approximately 200 km away, in the municipality of Le Prêcheur, Martinique, inhabitants find themselves trapped between the encroaching sea and the island’s active volcano. The inhabitants are very familiar with the lahars, these torrential mudflows laden with volcanic debris which race down the volcano’s sides.
“We are going to build a school, which will double as an emergency shelter for the inhabitants, and new housing for those who have to move,” says architect and urban planner Antoine Petitjean who is in charge of the project. The project aims to be an example for France’s overseas territories, offering attractive housing.
“We couldn’t pursue this project without involving the population right from the start,” continues the architect, in particular for choosing locally-sourced, sustainable materials for the future houses (wood, bamboo, gabion walls and rammed earth) and innovative industrial processes. “For more than a year, between 2019 and 2020, we organised two-week-long meetings every two months. We set up forums for working and retired farmers, and students. We established an overview of their lifestyles and surveyed their self-built homes. This allowed us to understand what the inhabitants considered to be essential and what was absolutely necessary to reproduce in the new neighbourhood.”
Persuading the inhabitants to relocate wasn’t the hardest part of the project. The lahars of 2018 were enough to convince them to move away from the coast towards the mornes*.
“Six years have passed since community engagement began and the current climate of hope generated by the project,” warns Antoine Petitjean.
Not all the problems have been resolved. In Martinique, where almost all the technical aspects of the first phase of works are in place and ready to launch, the green light has yet to be given because of a lack of institutional and regulatory support for the project: “If we wait too long, we risk undermining trust, especially if a disaster occurs before the project implementation,” says Antoine Petitjean.
In Guadeloupe, 31 of the 40 families have already been relocated and have settled into their new homes, while four families are completely opposed to moving. Not to mention a rumour that is doing the rounds: what if the local authorities are relocating people so they can get their hands on the land to build a seafront hotel? Virginie Bonot hasn’t thrown in the towel: “We will keep organising workshops to consult people, notably on the project of establishing collective gardens, creating a memorial area, planting mangroves, and so on.”
Ultimately, the rehousing projects in Le Prêcheur and Petit Bourg demonstrate an essential lesson: ensuring the safety of populations is not enough; ongoing dialogue and listening to their needs is indispensable🟡
Coordinate stakeholders and localities around managed retreat
Risk exposure is the primary factor for determining relocation sites. Once these vulnerabilities have been mapped, choosing the appropriate responses requires a comparison of the social, economic, and environmental costs, at short, mid and long terms. Regarding destination locations, while proximity within the same city is often preferable, it may not always be feasible. In any case, relocating assets and populations frequently disrupts connections between territories and involves numerous stakeholders and levels of governance.
The testimony of Gaël Perrochon from the Public Interest Group of Nouvelle Aquitaine, an administrative region of the Southwest of France, demonstrates the importance of integrating managed retreat at all governance and geographic scales – from neighbourhoods to municipalities, municipal partnerships and regional councils, and up to governments – to ensure policy coherence and overcome fragmented initiatives.
In the Southwest of France, managed retreat is being developed collectively
The administrative region of Nouvelle Aquitaine in the Southwest of France, with its 970-kilometre Atlantic shoreline, is particularly exposed to sea level rise impacts. In 2006 a Coastal Public Interest Group (GIP Littoral*), which brings together government bodies, the regional council, and intercouncil partnerships, was set up to provide coherent support to all municipalities concerned with establishing adaptation solutions to flood and erosion risks in Nouvelle Aquitaine.
“Currently, there are 13 local strategies for coastal management and GIP Littoral functions like a toolbox to provide knowledge for local authorities and help them develop their coastal strategies,” explains Gaël Perrochon of GIP Littoral. “We are working on strategies relating to risk management, as well as sustainable development projects for beaches and seaside towns. We also ensure that the recommended management methods correspond to local objectives and are coherent with the region-wide strategy adopted in 2012. For example, there would be no point in building a new defensive structure on the seashore to protect an isolated asset, such as a campsite, that has already been scheduled for relocation.”
GIP Littoral’s purpose is to put forward a proven working method based on the assessment and monitoring of local projects. This approach not only ensures effective project management but also enables elected officials to clearly communicate the rationale behind their decisions to citizens. Once the action plan is approved, local stakeholders can access funding to implement the proposed initiatives.
* GIP Littoral comprises the French State, the Regional Council of Nouvelle Aquitaine, the 4 Departmental Councils in the region (Charente-Maritime, Gironde, Landes, Pyrénées-Atlantique) and the 16 municipal intercouncils.
Up until now, most of the work has focused on publicly owned land. This has facilitated our operations on the ground. [...] Given the risks of disputes in the future, municipal councils don’t have the necessary means to implement actions relating to managed retreat."
Lacanau is one of the very first municipalities to have developed a management strategy for tackling coastal erosion. Considered as a national pilot test, the local strategy provides for the redevelopment of the seaside. The first and second phases involve the consolidation of the existing defences through sand replenishment operations, followed by works to increase the height of the rip-rap by 2050. But the town council is doing much more than that: “As early as 2017, the town council identified a high-risk area in its local urban plan to regulate urbanisation, and subsequently limited the number of buildings that can be built there in the future,” explains Gaël Perrochon. The town’s road network was also reviewed and the main artery, which leads to the beach, was reconfigured in order to benefit shops and businesses while providing space for nature to reinvest the seafront. Also, the town council is working on various timelines and is undertaking a feasibility study on managed retreat.
“Up until now, most of the work has focused on publicly owned land. This has facilitated our operations on the ground,” indicates Gaël Perrochon. But for many towns, executing planning projects and strategies is made considerably more complicated when it involves purchasing private assets. France’s Climate and Resilience law has provided the beginnings of a response with certain tools (tax rebate, special tenancy agreements, etc.). “Nevertheless, these tools can’t be deployed in their current form because there isn’t any funding, and municipal councils don’t have the necessary means to implement actions relating to managed retreat. Given the risks of disputes in the future, they will need to be strengthened from a legal standpoint.” This is a call for the State to address these issues and support municipalities accordingly🟡
Progressing, step by step, towards managed retreat
Adapting coastal cities to rising sea levels involves navigating multiple uncertainties regarding both climate change and the evolutions of our societies. While inevitable, uncertainties rarely align with political agendas. To meet this challenge, the scientific community like Hélène Rey-Valette, researcher at the University of Montpellier, France, recommend a dynamic approach based on the concept of adaptation pathways. This method allows stakeholders to contemplate profound changes, such as managed retreat strategies. In this context, managed retreat is envisioned as a gradual process over time, progressing step by step towards large-scale relocations, thanks to transitional and supportive policies.
Designing the pathway to managed retreat
The high variability that characterises climate change require us to adapt in a flexible manner, especially in coastal areas. Economist Hélène Rey Valette, senior researcher at Montpellier University and specialist in managed retreat, explains: “We need to approach the relocation of populations by developing adaptation pathways.” This involves the establishment of a timeline for what has to be undertaken, an itinerary for achieving an ultimate adaptation goal for a municipality, even if a specific date has not been set. “Initial measures can involve the relocation of public spaces, such as car parks, before focusing on movable assets and ultimately working towards buyouts of housing.”
The speed at which projects progress greatly depends on the level of vulnerability. That is the core idea of the pathway: “For example, the destruction of some buildings can wait ten or twenty years,” explains Hélène Rey Valette, although protection must be ensured during this interim period. “What is certain is that, from now on, local and national governments will no longer agree to help municipalities build dykes, install rip-rap or replenish beaches unless the relocation of buildings has really been planned for in the future.”
“It’s very complicated, especially for local elected representatives”, says the researcher, but also for the inhabitants. “We are not accustomed to thinking 30, 40 or even 50 years ahead.” It is difficult to be part of a transition made up of incremental changes that accumulate over the long term. Especially since a project lasting several decades cannot be set in stone and will inevitably change over time. “We need to think of these itineraries like Russian dolls, with measures that will stack or nest over time.”
We need to approach the relocation of populations by developing adaptation pathways.
One of the priorities for these coastal regions will be to rethink tourism and how it is funded, especially making the latter conditional upon the development of adaptation pathways. The issue is also considerable for the real estate market. “Property values will undoubtedly fall in certain areas, but they must not collapse entirely,” warns Hélène Rey Valette. An intergenerational approach can be key in that regard. It is not necessarily desirable to force elderly people to move but their descendants must be prepared for the fact that they will not be able to inherit, for example, the house.
“We are often lacking in collective imagination,” states Hélène Rey Valette. “Nevertheless, I believe we are on the right track. Fifteen years ago when we started talking about planned relocations, nobody listened. Today, much has changed. We are moving in the right direction.” Future paths cannot repeat past endeavours: “We must build and invent new models of public policies which allow us to anticipate.”🟡
Social justice, at the heart of the challenges of managed retreat
Social justice lies at the heart of every relocation effort. Balancing urgent responses with long-term planning can make it challenging to ensure equity, especially when pre-existing inequalities shape the landscape of adaptation policies. In the United States, cases such as Jean-Charles Island in Louisiana and Grand Forks in North Dakota illustrate how relocations not only expose but can also deepen disparities in power and wealth.
In this interview, A.R. Siders, a researcher at the University of Delaware, underscores the critical need to acknowledge and address these systemic imbalances. Her insights highlight the importance of integrating justice into adaptation strategies, ensuring that managed retreat does not reinforce existing inequities but instead fosters more sustainable and equitable outcomes.
In the United States, like anywhere else, managed retreat is foremost a question of social justice
Around the world, communities are relocated from prone-risk coastal areas, either as an emergency response or – in still very rare cases – as a planned solution. Regardless of the circumstances, those relocated must be rehoused. Do such rehousing plans incorporate social justice? “There are far more cases where social justice is lacking than where it is upheld,” signals A.R Siders, associate researcher at the University of Delaware, USA, “but things are progressing”.
While managed retreat can create situations of injustice, it’s not necessarily the cause. Sometimes it merely exposes pre-existing inequalities. On the Isle de Jean Charles, off the coast of Louisiana, a Native community was relocated in response to rising sea levels exacerbated by nearby oil-drilling operations. Although the relocations were well prepared, federal regulations denied these communities’ official tribal status, thus impeding them from obtaining the right to be rehoused in the new town which had been designated for them. “In this precise case, the lack of social justice pre-dated considerably the question of relocation, yet it had a direct impact,” explains A.R Siders.
A similar injustice occurs when displaced individuals receive financial compensation but are left to navigate the housing market on their own. While wealthier families can manage this transition, low-income households often struggle to secure suitable housing. “Once again, relocation often merely exposes existing social injustices.”
Relocation often merely exposes existing social injustices. [...] We need to learn from these previous experiences.
Another place, a different example: a relocation plan organised in Grand Forks in North Dakota, USA, did indeed offer new housing but came to an abrupt end. “These houses were two to three times more expensive than the ones previously lived in,” reveals the researcher. “The people simply could not afford them.”
Most of the time the people running the rehousing plans do their utmost to help, but find themselves thwarted by a lack of funding.
The objective is to plan ahead. In many places we know precisely what could occur in 20 or 30 years’ time. And yet, nothing is done until the disaster happens. “In the immediate aftermath, families are traumatised and in a great state of distress, sometimes having lost everything. Moreover, they must make the difficult decision to move out. This is not an effective approach. We must plan for the long term. Instead, relocation should be integrated into natural life cycles, such as job changes, retirements, or the desire to move to a different climate, then resettlements could be achieved more smoothly.” It is obviously much easier to regularly help small groups of people to move house than it is to move an entire community in one fell swoop.
“If we look at the example of Grand Forks, the idea of building houses was a good one. But by neglecting to think carefully about who they were being built for rendered the plan ineffective. We need to learn from these previous experiences.” Learn from past failures, therefore, to better manage retreat in the future🟡
Author: Marielle Court
Infographics of the Special Report
To delve deeper ...
Resources of the Ocean & Climate Platform
- Ocean & Climate Platform. (2023). Policy recommendations for coastal cities to adapt to sea level rsie. Sea’ties. 28 pages. https://bit.ly/recommendations_adapt_coastal_cities_SLR
- Ocean & Climate Platform (2021). IPCC Sixth Assessment Report: Sea level rise, impacts, vulnerabilities and adaptation. [Video]. https://youtu.be/IeeHU87SRyE
- Ocean & Climate Platform. (s.d.). Seaties. Ocean & Climate Platform https://ocean-climate.org/seaties/
Reports, guidelines and conferences
- “Agir Autrement”, Guide for co-constructing adaptation pathways for coastal areas (in French)
Rey-Valette H., Richard A., Perrochon G., Michel L., Bawedin V., Geneau E., Boschet C., Heurtefeux H., Robert S., Iziquel Y. André C. Brière C., Lanzellotti P., Bongarts T. Richard-Ferroudji A., d’Anglejan E., Costa S. Cabrit A., Crespy C., Renard M., Piquemal R., d’Artigues A., Hue J.D., 2025. « Agir Autrement » Guide pour co-construire des trajectoires d’adaptation des territoires littoraux. Rapport Projet Trajectoires Fondations de France, 142 p. https://www.cee-m.fr/wp-content/uploads/2025/02/AGIR-AUTREMENT.pdf
- Ademe’s Methodological guide to design local adaptation pathways to climate change (in French)
Ademe. (2019). Guide méthodologique : Construire des trajectoires d’adaptation au changement climatique du territoire. 979-10-297-1186-2. https://librairie.ademe.fr/changement-climatique/1165-construire-des-trajectoires-d-adaptation-au-changement-climatique-du-territoire.html
- New Zealand’s Guidance for Local Governments on “Coastal Hazards and Climate Change”
New Zealand Government, Ministry for the Environment. (2024). Coastal Hazards and Climate Change: Guidance for Local Government. 978-1-98-852535-8 https://environment.govt.nz/assets/publications/Files/coastal-hazards-guide-final.pdf
- PEERS’ Series of webinars on Adaptation Pathways
PEERS. (2022). Adaptation Pathways in Action: Creating Resilience to Sea Level Rise from Uncertainty at the Local Government Level in New Zealand. https://peerscoastal.org/get-involved/adaptation-pathways
IPCC Reports
- Glavovic, B.C., R. Dawson, W. Chow, M. Garschagen, M. Haasnoot, C. Singh, and A. Thomas, 2022: Cross-Chapter Paper 2: Cities and Settlements by the Sea. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp.2163–2194, doi:10.1017/9781009325844.019.
Scientific literature
- Brière, C., & Haasnoot, M. (2020). Gestion des risques littoraux et trajectoires d’adaptation par méthode DAPP. Keynote, JNGC 2020, 847-858. https://doi.org/10.5150/jngcgc.2020.092
- Haasnoot, M., Di Fant, V., Kwakkel, J., & Lawrence, J. (2024). Lessons from a decade of adaptive pathways studies for climate adaptation. Global Environmental Change, 88, 102907. https://doi.org/10.1016/j.gloenvcha.2024.102907
- Haasnoot, M., Kwakkel, J. H., Walker, W. E., & ter Maat, J. (2013). Dynamic adaptive policy pathways: A method for crafting robust decisions for a deeply uncertain world. Global Environmental Change, 23(2), 485-498. https://doi.org/10.1016/j.gloenvcha.2012.12.006
- Haasnoot, M., Lawrence, J., Magnan, A.K. (2021). Pathways to coastal retreat. Science, 372, 1287-1290. https://doi.org/10.1126/science.abi6594
- Mach, K. J., & Siders, A. R. (2021). Reframing strategic, managed retreat for transformative climate adaptation. Science, 372, 1294-1299. https://doi.org/10.1126/science.abh1894
- Rey-Valette H., Richard A., Michel L., Richard Ferroudji A., Heurtefeux H., Lecha V., Barral M., Cabrit A., Netter S. Lanzellotti P. (2024), « Retour sur la co-construction de stratégies de recomposition spatiale. Le cas de l’Occitanie (France) », VertigO – la revue électronique en sciences de l’environnement [En ligne], vol. 24, n°1, mis en ligne le 04 avril 2024, consulté le 20 mai 2024. URL : http://journals.openedition.org/vertigo/42990.
- Siders, A. R., Ajibade, I., & Casagrande, D. (2021). Transformative potential of managed retreat as climate adaptation. Current Opinion in Environmental Sustainability, 50, 272-280. https://doi.org/10.1016/j.cosust.2021.06.007
Authors: Sarah Palazot, Tess Segonds