Rate of Beach Loss Greatest with Near-term Sea Level Rise

Abstract

Shoreline hardening threatens beaches globally and is a problem that is expected to accelerate with sea level rise (SLR). Modeling risk of hardening for future beaches provides important data for resource managers, communities, and other stakeholders. However, few comprehensive studies of this issue exist. For all sandy beaches on Oʻahu, Hawaiʻi, we model modern (2015) and future (0.25, 0.46, 0.74 m of SLR) erosion hazard zones. We identify the relationships between coastal land use patterns and erosion hazard zones to define areas at risk of hardening. Our results show half of the beachfront shoreline will be at risk of hardening at 0.74 m of SLR. Shorelines become increasingly at risk of hardening throughout all SLR scenarios, with the largest increase (+7.4% island-wide) occurring between modern-day and 0.25 m of SLR. Modern-day and near-term hardening under 0.25 m of SLR pose maximum risk of beach loss because of heavy development on some shoreline segments. Coastal communities in other settings may be facing significant modern-day and near-term threats to beach resources that have not been identified. Adaptation to SLR should be considered an immediate need and not solely a future issue.