Reconstructing patterns of coastal risk in space and time along the US Atlantic coast, 1970–2016

Scott B Armstrong,Eli D Lazarus

doi:10.5194/nhess-19-2497-2019

Scott B Armstrong, Eli D Lazarus

Open Access

https://doi.org/10.5194/nhess-19-2497-2019

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Abstract

Abstract. Despite interventions intended to reduce impacts of coastal hazards, the risk of damage along the US Atlantic coast continues to rise. This reflects a long-standing paradox in disaster science: even as physical and social insights into disaster events improve, the economic costs of disasters keep growing. Risk can be expressed as a function of three components: hazard, exposure, and vulnerability. Risk may be driven up by coastal hazards intensifying with climate change, or by increased exposure of people and infrastructure in hazard zones. But risk may also increase because of interactions, or feedbacks, between hazard, exposure, and vulnerability. Using empirical records of shoreline change, valuation of owner-occupied housing, and beach-nourishment projects to represent hazard, exposure, and vulnerability, here we present a data-driven model that describes trajectories of risk at the county scale along the US Atlantic coast over the past 5 decades. We also investigate quantitative relationships between risk components that help explain these trajectories. We find higher property exposure in counties where hazard from shoreline change has appeared to reverse from high historical rates of shoreline erosion to low rates in recent decades. Moreover, exposure has increased more in counties that have practised beach nourishment intensively. The spatio-temporal relationships that we show between exposure and hazard, and between exposure and vulnerability, indicate a feedback between coastal development and beach nourishment that exemplifies the “safe development paradox”, in which hazard protections encourage further development in places prone to hazard impacts. Our findings suggest that spatially explicit modelling efforts to predict future coastal risk need to address feedbacks between hazard, exposure, and vulnerability to capture emergent patterns of risk in space and time.

Highlights

Risk reduction in developed coastal zones is a global challenge (Parris et al, 2012; Sallenger et al, 2012; Witze, 2018; Wong et al, 2014)
Our data-driven model generates a pattern of coastal risk that varies in space and time at the county scale along the US Atlantic coast (Fig. 1)
Our data-driven, spatio-temporal model of risk along the US Atlantic coast produces trajectories that vary in space and, on average, rise over time for all four chronic hazard scenarios that we test (Fig. 5)

Summary

Introduction

Risk reduction in developed coastal zones is a global challenge (Parris et al, 2012; Sallenger et al, 2012; Witze, 2018; Wong et al, 2014). Risk can be expressed as a function of hazard, exposure, and vulnerability. Vulnerability can reflect a wide variety of dimensions, but in physical terms (relative to social metrics) vulnerability generally represents the susceptibility of exposed property to potential damage by a hazard event (NRC, 2014). The reduction of disaster risk – across all environments, coastal settings – is an intergovernmental priority (UNISDR, 2015), a paradox has troubled disaster research for decades. Even as scientific insight into physical and societal dimensions of disaster events become clearer and more nuanced, the economic cost of disasters keeps rising (Blake et al, 2011; Mileti, 1999; Pielke Jr. et al, 2008; Union of Concerned Scientists, 2018)

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