Shifting Baselines May Undermine Shoreline Management Efforts in the United States

Rising sea levels, extreme weather events, and unsustainable coastal zone development pose threats to coastal communities. Shoreline development and hardening in at-risk areas can damage nearshore ecosystems, exacerbating existing risks to coastal populations. A comprehensive understanding of changes in response to development, storm events, and sea-level rise is needed to effectively mitigate coastal hazards and promote resilient coastlines. Informed mitigation and adaptation decisions require accurate and current coastal data. Lacking such data, coastal communities risk accepting increasingly degraded coastal zones and making poor management decisions based on shifted baselines. To determine whether human modification of shorelines can be accurately quantified over time, we evaluated shoreline classification efforts in the United States. Using these data, we estimated the current extent of US shoreline modification. However, we found that quantifying shoreline modification over time nationally is currently infeasible due to shoreline resolution changes associated with advances in mapping methodologies and a lack of regularly updated shoreline maps. We coupled this analysis with a survey of coastal planners and managers involved with US state shoreline mapping programs, which revealed that 20 US coastal states have undertaken shoreline mapping projects. However, of the 36 projects identified, only 18 had planned updates. Thus, we recommend increasing the scale and funding for several ongoing shoreline mapping efforts focused standardizing mapping techniques and establishing accurate shoreline condition baselines. Without accurate baselines and consistent updates to data, shorelines cannot be managed in a way that effectively mitigates coastal hazards while promoting socio-ecological resilience in a changing climate.