Managed retreat involves the purposeful, coordinated movement of people and buildings away from risks. This may involve the movement of a person, infrastructure (e.g., building or road), or community. It can occur in response to a variety of hazards such as flood, wildfire, or drought.
Politicians, insurers and residents have started paying increasing attention to managed retreat from low-lying coastal areas due to the threat of sea-level rise via climate change. Trends in climate change predict substantial sea-level rises worldwide, leading to coastal erosion that can significantly damage human infrastructure or put communities at risk of severe coastal flooding.
The type of managed retreat proposed depends on the location and type of natural hazard, and on local policies and practices for managed retreat. In the United Kingdom, managed realignment through removal of flood defenses is often a response to sea-level rise exacerbated by local subsidence. In the United States, managed retreat often occurs through voluntary acquisition and demolition or relocation of at-risk properties by government. In the Global South, relocation may occur through government programs. Some low-lying countries, facing inundation due to sea-level rise, are planning for the relocation of their populations, such as Kiribati planning for "Migration with Dignity".
In the United Kingdom, the main reason for implementating managed realignment is generally to improve coastal stability, essentially replacing artificial ‘hard’ coastal defences with natural ‘soft’ coastal landforms. According to University of Southampton researchers Matthew M. Linham and Robert J. Nicholls "one of the biggest drawbacks of managed realignment is that the option requires land to be yielded to the sea." One of the benefits, however, is that the process can help protect areas of land further inland by creating natural spaces that act as buffers to absorb water or dampen the force of waves.
Managed realignment has also been used to mitigate for loss of intertidal habitat. Although land reclamation has been an important factor for salt marsh loss in the UK in the past the majority of current salt marsh loss in the UK is believed to be due to erosion. This erosion may involve coastal squeeze, where protective sea walls prevent the landward migration of salt marsh in response to sea level rise when sediment supply is limited. Salt marshes are protected under the EU Habitats Directive as well as providing habitat for a number of species protected by the Birds Directive (see Natura 2000). Following this guidance, the UK’s biodiversity action plan aims to prevent net losses to the area of salt marsh present in 1992. It is, therefore, a legal requirement that all losses in marsh area must be compensated by replacement habitat with equivalent biological characteristics. This equates to the need to restore approximately 1.4 km² of salt marsh habitat per year in the UK. One of the major reasons cited for the slow pace of current salt marsh restoration in the UK is the uncertainty associated with the practice (Foresight).
There are no agreed protocols on the monitoring of MR sites and, consequently, very few of the sites are being monitored consistently and effectively. Due to the low levels of monitoring there is little evidence on which to base future managed realignment projects. This has led to the results of Managed Realignment schemes being extremely unpredictable.
Managed retreat in the form of relocation has been used in inland and coastal areas in response to severe flooding and hurricanes. In the United States, this often takes the form of "buyout" programs, in which government acquires and relocates or demolishes at-risk properties. In some cases, individual homes are purchased after disasters. In other cases, such as Odamah and Soldiers Grove, Wisconsin, or Valmeyer, Illinois, the entire community has relocated.
Managed retreat can be very controversial. A law suit in Del Mar California brought on by residents was initiated to stop a managed retreat program based on worries that home values, insurance costs and restricted home expansion have been effects of the policy. Some areas included in managed retreat are above sea level and are recommended based primarily on estimated engineering costs and by studies financed by the California Coastal Commission itself.
Despite the controversy, as the costs of climate change adaptation increase, more communities are beginning to consider managed retreat. One such community is Marina, California, adjacent to Monterey Bay. Marina's general acceptance of managed retreat became the subject of a Los Angeles Times feature article, published in 2020.
In the UK, the first managed retreat site was an area of 8,000 square metres (86,000 sq ft) at Northey Island in Essex flooded in 1991, followed by larger sites at Tollesbury and Orplands (1995), Freiston Shore (2001) and Abbott's Hall Farm, at Great Wigborough in the Blackwater Estuary, it is one of the largest managed retreat schemes in Europe. It covers nearly 280 hectares (690 acres) of land on the north side of the estuary (2002) and a number of others. The programme was started by the Essex Wildlife Trust (EWT) who own Abbott's Hall Farm. They made five breaches in the original old sea wall to allow the held-back sea to flood through to create salt marshland. The marshland over time reverted to its original state before cultivation, providing excellent bird habitat and breeding grounds.
- Salt marsh – Coastal ecosystem between land and open saltwater that is regularly flooded
- Restoration ecology – Scientific study of renewing and restoring ecosystems
- Environmental migrant – People forced to leave their home region due to changes to their local environment (an involuntary, forced case)
- Space and survival – Idea that long-term presence of human presence in the universe requires a spacefaring civilization (a hypothetical extreme case in science fiction)
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- Leatherman, S. P., Zhang, K., & Douglas, B. C. (2000). Sea level rise shown to drive coastal erosion. Eos, Transactions American Geophysical Union, 81(6), 55-57.
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- Hino, Miyuki; Field, Christopher B.; Mach, Katharine J. (May 2017). "Managed retreat as a response to natural hazard risk". Nature Climate Change. 7 (5): 364–370. Bibcode:2017NatCC...7..364H. doi:10.1038/nclimate3252.
- Mach, Katharine J.; Kraan, Caroline M.; Hino, Miyuki; Siders, A. R.; Johnston, Erica M.; Field, Christopher B. (1 October 2019). "Managed retreat through voluntary buyouts of flood-prone properties". Science Advances. 5 (10): eaax8995. Bibcode:2019SciA....5.8995M. doi:10.1126/sciadv.aax8995. PMC 6785245. PMID 31633030.
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- Ajibade, Idowu (2 September 2019). "Planned retreat in Global South megacities: disentangling policy, practice, and environmental justice". Climatic Change. 157 (2): 299–317. Bibcode:2019ClCh..157..299A. doi:10.1007/s10584-019-02535-1. S2CID 201716223.
McNamara, Karen E (May 2015). "Cross-border migration with dignity in Kiribati". Forced Migration Review.
The 'migration with dignity' policy is part of Kiribati's long-term nation-wide relocation strategy.
- Pethick, J. (2002). Estuarine and tidal wetland restoration in the United Kingdom: policy versus practice. Restoration Ecology, 10(3), 431-437.
- Linham, Matthew M.; Nicholls, Robert J. "Managed Realignment". ClimateTechWiki. Archived from the original on 17 October 2011. Retrieved 29 August 2018.[unreliable source?]
- Allen, J. R. L., & Pye, K. (1992). Coastal saltmarshes: their nature and importance. Saltmarshes: Morphodynamics, conservation and engineering significance, 1-18.
- Morris, R. K. A.; Reach, I. S.; Duffy, M. J.; Collins, T. S.; Leafe, R. N. (2004). "On the Loss of Saltmarshes in South-East England and the Relationship with Nereis diversicolor". Journal of Applied Ecology. 41 (4): 787–791. doi:10.1111/j.0021-8901.2004.00932.x. JSTOR 3505709.
- Hulme, Philip E. (28 September 2005). "Adapting to climate change: is there scope for ecological management in the face of a global threat?". Journal of Applied Ecology. 42 (5): 784–794. doi:10.1111/j.1365-2664.2005.01082.x.
- Crooks et al. 2001[full citation needed]
- Atkinson, Philip W.; Crooks, Steve; Drewitt, Allan; Grant, Alastair; Rehfisch, Mark M.; Sharpe, John; Tyas, Christopher J. (2004-09-23). "Managed realignment in the UK–the first 5 years of colonization by birds". Ibis. 146 (146): 101–110. doi:10.1111/j.1474-919X.2004.00334.x.
- Wolters, Mineke; Garbutt, Angus; Bakker, Jan P. (May 2005). "Salt-marsh restoration: evaluating the success of de-embankments in north-west Europe". Biological Conservation. 123 (2): 249–268. doi:10.1016/j.biocon.2004.11.013.
- Freudenberg, Robert (2016). Buy-in for buyouts: The case for managed retreat from flood zones. Cambridge, MA: Lincoln Institute for Land Policy. ISBN 978-1-55844-354-9. OCLC 1078995484.[page needed]
- Binder, Sherri Brokopp; Greer, Alex (28 December 2016). "The Devil Is in the Details: Linking Home Buyout Policy, Practice, and Experience After Hurricane Sandy". Politics and Governance. 4 (4): 97. doi:10.17645/pag.v4i4.738.
- Hersher, Rebecca (August 15, 2018). "Wisconsin Reservation Offers A Climate Success Story And A Warning". NPR.
- FEMA, Village Locals Reflect Moving Was Best Flood Protection
- Elam, Stephanie. "A flood forced this town to move. It could be a model for others hit by the climate crisis". CNN.
- Koslov, Liz (2 May 2016). "The Case for Retreat". Public Culture. 28 (2 79): 359–387. doi:10.1215/08992363-3427487.
- "Del Mar stands firm against 'planned retreat'". San Diego Union-Tribune. 22 May 2018.
- Local Assistance Grant Program, California Coastal Commission
- San Diego Union Tribune Article "Del Mar stands firm against 'Planned Retreat'"
- ESA Cost Benefit Presentation "Cost Benefit Analysis Methodology Overview" slide 24
- Gopal, Prashant (September 20, 2019). "America's Great Climate Exodus Is Starting in the Florida Keys". Bloomberg.
- Xia, Rosanna (24 February 2020). "Most California cities refuse to retreat from rising seas. One town wants to show how it's done". Los Angeles Times. Archived from the original on 1 March 2020.
- Information on Abbott's Hall from Essex Wildlife Trust
- Pictures of the Tollesbury and Orplands managed retreat sites
- Board on Environmental Studies and Toxicology, 2001. Compensating for Wetland Losses Under the Clean Water Act
- The UK Environment Agency’s Managed Realignment Electronic Platform
- The Online Managed Realignment Guide (OMReG): A website designed to act as a 'collecting point' for information about coastal Managed Realignment and Regulated Tidal Exchange projects in the UK and Northern Europe
- Managed Coastal Retreat: A Legal Handbook on Shifting Development Away from Vulnerable Areas
- Animation explaining basic principle of Managed Realignment