80 Years of Coastal Erosion and Accretion in Aotearoa New Zealand

Understanding historical coastal change over multi‐decadal timescales is fundamental for coastal hazard assessment and adaptation planning. In Aotearoa New Zealand (NZ), national‐scale coastal change information has historically been fragmented, limited in spatial resolution or constrained to relatively short timeframes. Here, we present an overview and initial analysis of New Zealand's Coastal Change Dataset (NZCCD), a nationally consistent dataset of manually mapped historical coastline positions (with relatively low positional uncertainty averaging 4.1 m, depending on scale) and coastal change rates spanning the 1940s to 2024 for most of NZ's open coast beaches and soft cliffs. Results demonstrate that NZ's coastline is highly dynamic over multi‐decadal timescales. Approximately 42% of the mapped coastline has undergone net accretion, 40% net erosion, with 18% showing no resolvable long‐term trend. Rates of erosion and accretion are generally <2 m y −1 , but localised hotspots of rapid change (both erosion and accretion) exceeding ±10 m y −1 are identified. Multi‐decadal and low temporal resolution baseline datasets with national coverage, such as the NZCCD, are complementary to high temporal resolution, semi‐automated satellite‐derived studies. The dataset enables national‐scale and locally relevant decision‐making in the context of climate change and relative sea‐level rise.