Can It Happen Here? Managed Retreat for US Cities
Update for an INC project - Feedback welcome!
For several months John and I have been studying what's known and done about "managed retreat," to understand how US cities might be prompted to adopt this ignored strategy for climate adaptation. We've developed some initial ideas, a hypothesis, and some framing of the landscape within which decisions about managed retreat are made. And there's more research and thinking to do. Here's what we have so far:
The typical dynamics of urban development block most US cities from planning—or even considering—a “managed retreat” strategy to prepare for climate changes that could cause parts of the city to be uninhabitable or unusable in this century. Retreat-- removing development and relocating people, businesses, and infrastructure—would produce a great deal of political, financial, and community pain and little tangible gain in the short run. This is true even in cities that have undergone a horrendous climate disaster; their instinct is to rebuild their development/spatial footprint, perhaps protecting it more, but not adjusting its expanse to avoid future risks.
And yet, climate changes are projected to make parts of many cities inhabitable and unusable during this century. Rising sea levels and more frequent and intense rainfall will cause chronic flooding and erosion in coastal and riverside communities. By 2060, more than 270 coastal US communities will be chronically inundated, given moderate sea-level rise, according to a 2017 study by the Union of Concerned Scientists. More rapid sea-level rise could chronically inundate nearly 670 coastal communities by 2100, including 50 heavily populated cities, among them: Oakland, Miami, New York City.[1] Prolonged droughts will cause severe water shortages and waves of extreme heat will make it dangerous to be outside. El Paso, Las Vegas, Phoenix, and other cities in the southwest US are located in arid environments that have natural scarcity of water and precipitation and are becoming hotter and drier, a 2017 Arup report noted, adding that the nation’s arid zone is expanding.[2]
Cities that do anticipate these climate risks usually plan to build their way out of the problem: build more barriers to sea and river surges, more capacity for storm water drainage and water delivery, and more electricity-generation capacity to power more air conditioners to cool buildings. They also plan to move out of climate-harm’s way any underground and street-level infrastructure that could be inundated.
Only a few US cities have included managed retreat in their plans, and some of these are hardly examples of best practice. In April 2018, California’s Coastal Commission forced Del Mar, with about 4,100 residents, to include a retreat strategy in its coastal resilience plan or lose local authority over future development.[3] New Orleans started a retreat strategy (property buy outs) after Hurricane Katrina, but then abandoned it. The US Army Corps of Engineers included retreat—“real estate acquisition and/or relocation”—in its October 2017 flood management recommendations for coastal Norfolk, Virginia, along with many structural defenses, but the overall plan’s $1.8 billion price tag is bigger than the city’s annual budget and depends in large part on receiving a special federal appropriation.[4]
In view of this situation, the Innovation Network for Communities is creating a framework to help answer this question: how can managed retreat become a general planning practice of US cities? The framework redefines managed retreat, describes four pathways that can lead cities to choose to retreat, and identifies the city capacities needed to prepare, implement, and defend decisions about which pathway(s) to managed retreat are being taken. It examines an initial hypothesis: that market dynamics are the most likely force that will lead cities to consider and embrace managed retreat. And it proposes several next steps.
| An Initial Hypothesis
Based on initial research, our hypothesis is that city consideration of managed retreat may follow any or a combination of four pathways, each of which has different instigating actors and approaches to retreat, with different implications for what a city will have to deal with. The pathways are:
The Market Dynamics pathway appears to be the one most likely to be taken in many cities—with distinct implications for what cities will need to do. |
Defining Managed Retreat
Most literature and news reports about managed retreat focus on the elimination of existing physical infrastructure and housing and the subsequent relocation of people due to retreat-inducing threats posed by flooding due to rising seas and rivers. For research purposes, we have framed managed retreat more broadly in two ways. Our definition includes the prevention of future development, not just the dismantling of existing development, because relinquishing development is also a consequential retreat from a city’s future land-use footprint. And we have considered the climate risks that, in addition to chronic flooding, may be posed by extreme heat and drought as another potential driver of city retreat.
“Managed retreat” is the use of public policies, including regulation and investment, to over time eliminate or prevent development from areas that are:
- At significant risk of recurrent or permanent damage or destruction from climate effects
- Needed in an undeveloped, natural condition in order to protect other development that is at significant climate risk (e.g., green space designed to absorb flood waters)
When eliminating development also involves relocation of people and businesses, managed retreat may include resettlement and engagement of “receiving communities” where relocation is to occur.
“Development” means physical uses of land, especially the building of physical infrastructure. These uses generate economic, social, and environmental impacts, as well as various risks from disruption, damage, and destruction that are not just due to climate change (e.g., other natural disasters, accidents, economic cycles, warfare).
“Climate risks” that may trigger managed retreat are new, regularly recurring or prolonged—chronic—climate patterns, such as extreme high tides and sustained extreme heat waves or increased aridity, which can overwhelm a city’s resilience and damage or destroy physical, social, economic, and environmental assets.
Essentially, managed retreat changes the use of and development of land and/or water in anticipation of climate hazards the city cannot sufficiently manage or afford through other means or chooses not to pay for. It involves an engineering, financial, social, and political calculation.
Managed retreat is one of four approaches to climate adaptation focused on preparation and prevention, rather than post-disaster emergency response and rebuilding. Cities may plan and use these approaches in various combinations.
| Protection | Protecting physical, social, economic, and environmental assets by reducing their exposure to climate events (e.g., building barriers to inundation, adding green infrastructure to reduce storm surges or heat). |
| Accommodation | Adjusting assets to reduce their potential vulnerability to climate events (e.g., moving building systems to roofs, increasing the air conditioning of buildings, “day lighting” waterways) |
| Creation of Usable Land | Making more developable or arable land and protecting it (e.g. reclaiming land from the sea; increasing the amount of irrigated agricultural land near city). |
| Managed Retreat | Using public policies to over time eliminate or prevent development from areas at significant risk of recurrent or permanent damage from climate effects or needed in an undeveloped condition to protect other at-risk development. |
Retreat may occur at multiple scales, including:
- Individual properties/parcels, sites
- Public infrastructure (roads, wastewater treatment plants, etc.)
- Sub-districts/neighborhoods of cities
- Entire cities
- Urban metropolitan regions
- Regions of a country (rural and urban areas)
Managed retreat should be differentiated from climate migration, which involves the (largely) unplanned and unrequired movement of individuals and businesses away from areas that are under extreme climatic stress or perceived to be at high risk and to areas of greater safety and viability.
US cities have a critical role to play in determining whether and how to use managed retreat as a part of their climate adaptation plans, because they have substantial control over local land uses and, therefore, over development, and they are the primary locus of retreat’s benefits, burdens, and challenges. However, cities operate in policy contexts set by state and federal governments and in the US legal context, which substantially affect the use of managed retreat.
Although managed retreat may be triggered proactively by analysis that anticipates a city’s climate risks, in most cases to date it has occurred reactively, in the wake of a damaging climatic experience such as a storm surge, which then leads to analysis of future risks and recognition that an unmanageable chronic risk is emerging.
Climate-Risk Drivers that Lead to Consideration of Retreat
In general, it is easier to strengthen a city’s resilience to acute climate shocks and therefore hope to avoid retreat choices, than it is to manage chronic climate shocks. However, acute risks may just be the prelude to chronic risks—what appears to be an episodic and manageable pattern may become an accelerating, intensifying, and unmanageable pattern.
The great majority of serious retreat planning has taken place in response to either riverine flooding or sea-level rise. In delta cities, riverine flooding and sea-level rise may combine to exacerbate risks. Some smaller, low-lying islands are at risk of complete, long-term inundation from sea-level rise. Other types of climate impact that may motivate retreat include:
- Extreme rain events (e.g., “cloudbursts”) pose the risk of chronic flooding of low-lying area infrastructure and buildings.
- Prolonged extreme heat poses the risk of illness and death of vulnerable populations such as children, the elderly, and people with chronic diseases. At certain levels of heat, it can become unsafe for humans to be out of doors or indoors without effective cooling systems.
- Droughts and increased aridity (dry, barren land) pose the risk of insufficient water for household, agricultural, or industrial use, a potential limit to a city’s carrying capacity.
Potential Benefits of Managed Retreat
Cities can achieve several potential benefits through managed retreat:
- Protect the Safety and Health of People. Retreat can prevent future injuries, loss of life, and health problems.
- Maintain the Usefulness of Physical and Business Assets. Retreat can ensure the continuing usefulness of physical assets (rerouting a coastal highway), prevent disruption of business, or protect other development from climate risks (e.g., removing development from a floodplain so that more of the flooding will be soaked up before it reaches parts of the city).
- Avoid Future Financial Costs. Retreat can prevent the need for spending on emergency responses to climate disasters and on recovery/rebuilding after disasters. It can also reduce/eliminate financial costs that would be needed instead to protect and accommodate development against climate risks.
- Prevent and Reduce Inequities. Retreat can ensure that the city addresses and prioritizes, rather than overlooks or discriminates against, the interests of disadvantaged individuals, households, and neighborhoods, which are often the most vulnerable to damage due to climate events.
- Preserve Community Cohesion. Retreat can allow the relocation of a group of people in a place as an intact community, rather than the piecemeal abandonment of at-risk properties that might otherwise occur.
- Enhance Ecosystem Services. Retreat can allow enhancement of the capacity of local ecosystems (e.g., wetlands) to provide environmental benefits in addition to improvement in climate resilience (e.g., habitat restoration).
Retreat Strategies
Cities can use multiple strategies to eliminate or prevent development from areas where chronic, potentially disastrous climate risks rule out other climate-adaptation approaches.
To eliminate existing development:
- Invest in Property Acquisition. Cities can purchase property in at-risk areas from voluntary sellers and then remove development and prevent additional development.
- Mandate Removal of Development. Cities can use legal and regulatory processes to require relocation from at-risk areas—immediately or over the long term—but they must compensate property owners and may need to facilitate resettlement of individuals, communities of people, and businesses.
- Prohibit Protection and Accommodation Actions. Cities can preclude property owners from taking certain protection or accommodation actions (e.g., building sea walls), which over time may result in the owners voluntarily retreating from the property.
To prevent future development:
- Constrain Future Development and Post-Disaster Rebuilding. Cities can place conditions on future development that could preclude development activities, such as by increasing the cost of development beyond what the market is willing and able to pay, or restricting rebuilding after a disaster in at-risk areas.
- Prohibit Future Development. Cities can regulate land use to prevent new or additional development in at-risk areas—in order to preserve environmental services for climate resilience, support agricultural uses of land to secure food supply, or foster increased densification of the already built city.
To both eliminate and prevent development:
- Limit Support and Services for Development. Cities can limit/reduce/eliminate suport for infrastructure and services in high-risk areas, such as availability of roads, water, and electricity. Some limitations may be due to factors cities cannot control, such as lack of water or electricity generation to support certain levels of population and agricultural or industrial activities in cities in arid areas.
[1] The study defined “chronic inundation” as flooding that occurs 26 times per year (on average, once every other week) or more over at least 10 percent of the land in a community. https://www.ucsusa.org/sites/default/files/attach/2017/07/when-rising-seas-hit-home-full-report.pdf
[2] https://www.arup.com/publications/research/section/cities-alive-cities-in-arid-environments.
[3] http://www.sandiegouniontribune.com/communities/north-county/sd-no-managed-retreat-20180417-story.html.
[4] https://insideclimatenews.org/news/30102017/norfolk-sea-level-rising-flood-protection-plan-army-corps-engineers-climate-change
