This project analyzed the ways in which natural forces, economic decisions, and public policies interact over long time horizons in coastal settings to determine how the built environment and patterns of human settlement react to rising seas and related coastline changes.  The project used empirical research and modeling to quantify feedbacks between human behavior and coastal landscape change, analyze household risk perceptions and responses to risk, explore future coastal evolution, and inform potential policy responses. 

The empirical work examined feedbacks between natural hazards, adaptation, and community characteristics highlighting the unintended consequences of adaptation and demographic disparities in exposure to environmental risks.  Analysis of coastal development patterns showed that investment in beach nourishment projects accelerated residential development and increased property value at risk to future natural disasters. Hurricanes also reduce the average probability of redevelopment on barrier islands but accelerate oceanfront re-development where structural damage from erosion and hazards is severe.

To ground the modelling efforts in real-world perspectives, the project included multiple waves of coastal household surveys in Dare County, NC and Worcester County, MD, and these data were combined with housing attributes (from tax assessor database) and flood risk measures (from FEMA, National Weather Service, and First Street Foundation). The surveys focused on beliefs and attitudes about environmental change and coastal risk management, risk perceptions, self-protection behaviors (e.g., insurance and mitigation), and included a field experiment to measure individual risk perceptions. These data provide the basis for empirical analysis of risk perceptions and behaviors, exploration of hypotheses about coastal decision-making under risk & uncertainty, and help to ground simulations of coastal evolution in human dimensions. 

An agent-based model was developed using insights from the surveys and previous modeling work.  The model simulates coastal real estate markets and incorporates physical forcing from beach erosion, dune dynamics, and sea-level rise as well as external economic forcing from changes in real estate markets in other locations.  Model results highlight two mechanisms that can dampen climate signals in property values and delay the inevitable collapse of property values with inundation due to sea level rise (SLR): government subsidies to coastal management that maintain wider beaches, and arbitrage opportunities for purchasing real estate in outside markets that attract residents with higher incomes and willingness to pay for coastal living. 

A numerical model focusing on the physical system, with explicit couplings to the human system, was also built that includes representations of barrier island dynamics such as erosion, dune building, and inlet evolution -- as well as modules representing human management actions employed to defend transportation corridors and communities.  Model experiments explored the effects present management practices on barrier evolution. Results suggest that under conditions of SLR, barriers can become uninhabitable (too low or too narrow to support roadways or communities) within decades to centuries of initiation of coastal management. The time to uninhabitability depends on management practices, such as the height to which dunes are rebuilt. In addition, the pathway toward uninhabitability also depends on natural dune growth rates, exogenous conditions (SLR rate and storminess), initial barrier height, and on how management patterns vary alongshore. Results of model experiments involving alongshore-variable management show that system-wide transitions to less vulnerable states are possible through early abandonment of low-lying infrastructure, even under accelerated SLR and increased storminess.

Overall, this research provided conceptual and empirical insights with a suite of modeling tools that can explain how dense coastal settlements arrived at their current configuration and look forward in time when new responses to coastal and environmental changes will necessarily occur.  The results advanced knowledge about how the coupled coastal-economic system will likely respond to an increasingly precarious future.  The theoretical advances translate to other coupled human-environmental systems facing present and future climate pressure and other environmental shocks.  The ramifications of the results for coastal populations living along barrier islands has already begun to resonate with stakeholders and will continue to inform the ways that these regions unwind from a static defense against the rising ocean.  Ideally, results from this project will help to smooth the transition from the current forms of human occupation and interactions along the coastline to a future that avoids sudden, catastrophic changes.

Last Modified: 10/12/2023
Modified by: Dylan Mcnamara