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Retreat from some areas will become unavoidable under intensifying climate change. Existing deployments of managed retreat are at small scale compared to potential future needs, leaving open questions about where, when, and how retreat under climate change will occur. Here, we analyze more than 40,000 voluntary buyouts of flood-prone properties in the United States, in which homeowners sell properties to the government and the land is restored to open space. In contrast to model-based evaluation of potential future retreat, local governments in counties with higher population and income are more likely to administer buyouts. The bought-out properties themselves, however, are concentrated in areas of greater social vulnerability within these counties, pointing to the importance of assessing the equity of buyout implementation and outcomes. These patterns demonstrate the challenges associated with locally driven implementation of managed retreat and the potential benefits of experimentation with different approaches to retreat.

F aced with global warming, rising sea levels, and the climate-related extremes they intensify, the question is no longer whether some communities will retreat-moving people and assets out of harm's way-but why, where, when, and how they will retreat. To the extent that retreat is already happening, it is typically ad hoc and focused on risk reduction in isolation from broader societal goals. It is also frequently inequitable and often ignores the communities left behind or those receiving people who retreat. Retreat has been seen largely as a last resort, a failure to adapt, or a one-time emergency action; thus, little research has focused on retreat, leaving practitioners with little guidance. Such a narrow conception of retreat has limited decision-makers' perception of the tools available and stilted innovation. We propose a reconceptualization of retreat as a suite of adaptation options that are both strategic and managed. Strategy integrates retreat into long-term development goals and identifies why retreat should occur and, in doing so, influences where and when. Management addresses how retreat is executed. By reconceptualizing retreat as a set of tools used to achieve societal goals, communities and nations gain additional adaptation options and a better chance of choosing the actions most likely to help their communities thrive.We argue for strategy that incorporates socioeconomic development and for management that is innovative, evidence-based, and context-specific. These are not radical alterations to adaptation practice-adaptation planning often starts with identifying the goals people have, and context-specific implementation has long been a central tenet of adaptation-but they have been underapplied to retreat. Retreat is hard to do and even harder to do well, for many reasons: short-term economic gains of coastal development; subsidized insurance rates and disaster recovery costs; misaligned incentives between residents, local officials, and national governments; imperfect risk perceptions; place attachment; and preference for the status quo (1-6). A reconceptualization could make strategic, managed retreat an efficient and equitable adaptation option.

High-tide flooding reduces customer access to businesses, and impacts are projected to increase sharply with sea level rise.

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Tide gauge water levels are commonly used as a proxy for flood incidence on land. These proxies are useful for projecting how sea‐level rise (SLR) will increase the frequency of coastal flooding. However, tide gauges do not account for land‐based sources of coastal flooding and therefore flood thresholds and the proxies derived from them likely underestimate the current and future frequency of coastal flooding. Here we present a new sensor framework for measuring the incidence of coastal floods that captures both subterranean and land‐based contributions to flooding. The low‐cost, open‐source sensor framework consists of a storm drain water level sensor, roadway camera, and wireless gateway that transmit data in real‐time. During 5 months of deployment in the Town of Beaufort, North Carolina, 24 flood events were recorded. Twenty‐five percent of those events were driven by land‐based sources—rainfall, combined with moderate high tides and reduced capacity in storm drains. Consequently, we find that flood frequency is higher than that suggested by proxies that rely exclusively on tide gauge water levels for determining flood incidence. This finding likely extends to other locations where stormwater networks are at a reduced drainage capacity due to SLR. Our results highlight the benefits of instrumenting stormwater networks directly to capture multiple drivers of coastal flooding. More accurate estimates of the frequency and drivers of floods in low‐lying coastal communities can enable the development of more effective long‐term adaptation strategies.

The year 2020 saw further devastating floods, caused by storms such as Cyclone Amphan in South Asia and a record-breaking hurricane season in the Atlantic Ocean. It is now clear that the changing climate is making coastal flooding more frequent, downpours heavier and storms wetter. Less appreciated is that the impacts of increased flooding are distributed unequally and unfairly. The greatest burdens fall on the most vulnerable.