INTEGRATED ASSESSMENT OF THE EMERGING RISKS OF HIGH-TIDE FLOODING

Abstract

High-tide flooding (HTF), also called “sunny-day flooding” or “nuisance flooding,” is an emerging coastal hazard that is becoming more frequent as sea levels rise and coastal development intensifies. While typically low in depth and localized in extent, HTF occurs with increasing frequency and persistence, producing cumulative socio-economic impacts that threaten infrastructure, property, livelihoods, and public health. However, understanding of HTF risks, their distribution across groups, and resources for responding to these impacts are poorly understood. As a result, flood risk management systems remain largely storm-centric, with limited capacity to address recurrent, low-intensity events. This dissertation asks: How does the emerging risk of high-tide flooding affect coastal communities, and how do current flood risk management practices respond to these risks? This dissertation is guided by the hazard–exposure–vulnerability–response (HEVR) framework that links the physical and socio-economic aspects of flood risks with the mitigating influence of responses to these risks. The dissertation consists of an Introduction chapter that introduces the topic of HTF, followed by 3 chapters exploring different aspects of HTF risks and their risk management implications, and finally, a Conclusion chapter. After first introduction chapter, Chapter 2 presents a systematic review of 194 studies published between 1985 and 2024 that examine HTF impacts. The review synthesizes evidence of socio-economic consequences across infrastructure, private property, local economies, and vulnerable populations. It identifies major challenges, including inconsistent definitions, limited geographic coverage outside the U.S., and fragmented impact measures that hinder comparability. Chapter 3 draws on semi-structured interviews with 36 planners, engineers, and stormwater managers in coastal North and South Carolina. Results show that practitioners conceptualize HTF through diverse local terms and drivers—tides, wind, rain, and coastal development—and often adapt storm-based strategies to manage it, while recognizing that efforts to develop HTF-specific responses remain in an exploratory stage. Chapter 4 analyzes a household survey (n = 111) in Charleston, South Carolina, stratified by GIS-based exposure. Findings reveal uneven distributions of HTF exposure, perceived impacts, and access to adaptation resources. Households with seniors and that were transit-dependent reported greater disruptions and damages yet had less financial protection through insurance, showing that those most affected have the least financial safeguards against recurring losses. Together, the dissertation reveals that the impacts of HTF as a distinct, non-storm hazard are shaped by multiple interacting drivers beyond tides and are characterized by uneven exposure, interconnected vulnerabilities, and inequitable responses. It advances scholarship and informs practice by highlighting the need for definitions that are both scientifically standardized and locally accurate, for site-specific exposure assessments, and for equity-focused adaptation strategies. Together, these insights support the development of a more comprehensive and equitable foundation for managing the risk of recurrent coastal flooding.