Shifting Baselines May Undermine Shoreline Management Efforts in the United States

Riordan Correll-Brown,Carter S Smith,Devon O Eulie,Mariko A Polk,Emory H Wellman,Rachel K Gittman,Steven B Scyphers

doi:10.3389/fclim.2022.719109

Abstract

Rising sea levels, extreme weather events, and unsustainable coastal zone development pose serious threats to growing coastal communities. Human actions, such as shoreline development and hardening in at-risk areas, can damage nearshore ecosystems and exacerbate existing risks to coastal populations. A comprehensive understanding of shoreline changes in response to development, storm events, and sea-level rise is needed to effectively mitigate coastal hazards and promote adaptive and resilient coastlines. To determine whether human modification of shorelines can be accurately quantified and assessed over time, we evaluated past and present shoreline mapping and classification efforts in the United States. We coupled a review of available US shoreline data with a survey of coastal planners and managers involved with US state shoreline mapping programs. Using these data, we estimated the current extent of shoreline modification along the Atlantic, Pacific, and Gulf US coasts. However, we found that quantifying shoreline modifications over time nationally—or even within a single state—is currently infeasible due to changes in shoreline resolution associated with advances in shoreline mapping methodologies and a lack of regularly updated shoreline maps. State-level analysis from surveys revealed that 20 US coastal states have undertaken shoreline mapping projects, with sixteen tracking shoreline type and/or condition. However, of the 36 shoreline maps and databases identified, only half (18) were updated regularly or had planned updates. Lacking shoreline change data, coastal communities risk accepting increasingly degraded coastal zones and making poor management decisions based on shifted baselines. Thus, we recommend increasing the scale and funding for several ongoing innovative shoreline mapping efforts. These efforts are particularly focused on improving and standardizing shoreline mapping techniques, as well as establishing accurate baselines for shoreline conditions in the United States. Without accurate baselines and regular, consistent updates to shoreline data, managers cannot manage shorelines in a way that effectively mitigates coastal hazards while also promoting socio-ecological resilience in a changing climate.

Highlights

Global coastal zones are home to dense and increasing populations
Environmental Sensitivity Index (ESI) data are derived from a variety of sources at the local and national levels; including pre-existing datasets provided by state agencies and universities, aerial imagery, National Oceanic and Atmospheric Administration (NOAA) Continually Updated Shoreline Product (CUSP) data, NOAA national shoreline data, data from NOAA’s coastal change analysis program (C-CAP) and data collected for the ESI update effort (Petersen et al, 2019)
“solid man-made structures” (ESI types 1B and 8B) were the most prevalent type of shoreline modification, representing 17,211 km or 61% of hard structures; this category includes “[solid, non-riprap] revetments, seawalls, piers, and docks constructed of concrete or wood” (NOAA, 2019)

Summary

Introduction

Global coastal zones are home to dense and increasing populations. the world’s coast represents only 20% of the global land area, it hosts 41% of the world’s population (Martínez et al, 2007). From 2003 to 2015 alone, the US coastal population increased by 14.3 million people (Martínez et al, 2007), and there is no indication that this growth will slow in the coming decades (Neumann et al, 2015). On the US East Coast, roughly 60% of land lying below the benchmark of one meter above sea level is projected to be developed and populated, according to current state and local government land-use plans (Titus et al, 2009). In these areas of low elevation, the threats of storm surge, sea-level rise (SLR), and flooding are most acute. Alterations in storm climatology are expected to increase the frequency and severity of these flood events (Trenberth, 2005; Elsner et al, 2008)

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