Assessing the full costs of floodplain buyouts.

Given projected increases in flood damages, managed retreat strategies are likely to become more widespread. Voluntary buyouts, where governments acquire flood-damaged properties and return the sites to open space, have been the primary form of federally funded retreat in the USA to date. However, little attention has been paid to the cost structure of buyout projects. Using a transaction cost framework, we analyze the costs of activities that comprise floodplain buyouts. Federal data do not distinguish transaction costs, but they do suggest that the cost of purchasing properties often accounts for 80% or less of total project costs. Through a systematic review (n = 1103 publications) and an analysis of government budgets (across n = 859 jurisdiction-years), we find limited sources with relevant cost information, none of which reports transaction costs. The absence of activity-level cost data inhibits more targeted policy reform to support community-driven and efficient buyout programs. Better data collection and reporting can inform more impactful and equitable buyout policy.

The effect of information about climate risk on property values.

Floods and other climate hazards pose a widespread and growing threat to housing and infrastructure around the world. By reflecting climate risk in prices, markets can discourage excessive development in hazardous areas. However, the extent to which markets price these risks remains poorly understood. Here we measure the effect of information about flood risk contained in regulatory floodplain maps on residential property values in the United States. Using multiple empirical approaches and two decades of sales data covering the universe of homes in the United States, we find little evidence that housing markets fully price information about flood risk in aggregate. However, the price penalty is larger for commercial buyers and in markets where buyers are more risk aware, suggesting that policies to improve risk communication could influence market outcomes. Our findings indicate that houses in flood zones in the United States are currently overvalued by a total of $43.8 billion (95% confidence interval: $32.6 to $55.6 billion) based on the information in publicly available flood hazard maps alone, raising concerns about the stability of real estate markets as climate risks become more salient and severe.

Risk screening methods for extreme heat: Implications for equity-oriented adaptation.

Morbidity and mortality impacts of extreme heat amplified by climate change will be unequally distributed among communities given pre-existing differences in socioeconomic, health, and environmental conditions. Many governments are interested in adaptation policies that target those especially vulnerable to the risks, but there are important questions about how to effectively identify and support communities most in need of heat adaptations. Here, we use an equity-oriented adaptation program from the state of California as a case study to evaluate the implications of the currently used environmental justice index (CalEnviroScreen 3.0) for the identification of socially vulnerable communities with climate change adaptation needs. As CalEnviroScreen is geared towards air and water pollution, we assess how community heat risks and adaptation needs would be evaluated differently under two more adaptation-relevant vulnerability indices: the Social Vulnerability Index and the Heat-Health Action Index. Our analysis considers communities at the census tract scale, as well as the patterns emerging at the regional scale. Using the current index, the state designates 25% of its census tracts as "disadvantaged" communities eligible for special adaptation funds. However, an additional 12.6% of the state's communities could be considered vulnerable if the two other indices were considered instead. Only 13.4% of communities are vulnerable across all three vulnerability indices studied. Choice of vulnerability index shapes statewide trends in extreme heat risk and is linked to a community's likelihood of receiving heat-related California Climate Investments (CCI) projects. Tracts that are vulnerable under the current pollution-focused index, but not under the heat-health specific index, received four times the number of heat-related interventions as tracts vulnerable under the reverse scenario. This study demonstrates important nuances relevant to implementing equity-oriented adaptation and explores the challenges, trade-offs, and opportunities in quantifying vulnerability.

Managed retreat through voluntary buyouts of flood-prone properties.

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.

High-tide flooding disrupts local economic activity.

Evaluation of observed sea level rise impacts to date has emphasized sea level extremes, such as those from tropical cyclones. Far less is known about the consequences of more frequent high-tide flooding. Empirical analysis of the disruption caused by high-tide floods, also called nuisance or sunny-day floods, is challenging due to the short duration of these floods and their impacts. Through a novel approach, we estimate the effects of high-tide flooding on local economic activity. High-tide flooding already measurably affects local economic activity in Annapolis, Maryland, reducing visits to the historic downtown by 1.7% (95% confidence interval, 1.0 to 2.6%). With 3 and 12 inches of additional sea level rise, high-tide floods would reduce visits by 3.6% (3.2 to 4.0%) and 24% (19 to 28%), respectively. A more comprehensive understanding of the impacts of high-tide flooding can help to guide efficient responses from local adaptations to global mitigation of climate change.