New research shows that California has lost about 60% of its coastal sand dunes since the mid-1800s, reshaping one of the state's most important natural buffers. The study estimates a decline of roughly 442 square kilometers, even as a small amount of new dune area formed in some places through sand buildup on the seaward edge.
These landscapes do more than define the shoreline. They help shield coastal communities from flooding and provide habitat for native plants and wildlife, including protected birds such as least terns and western snowy plovers. But dunes often sit on land that is also attractive for roads, housing, and other development, making them especially vulnerable over time.
To build a fuller picture of how the coastline has changed, researchers compared historical maps with modern aerial imagery and lidar data. They combined machine learning with manual identification to locate current dune systems and track how their extent has shifted across nearly two centuries.
The findings show that many dunes were replaced by infrastructure, while others were worn down by erosion. Invasive grasses also reduced the resilience of some dune systems by competing with native species and complicating restoration efforts. The remaining dunes are now more fragmented, which can weaken their ecological value.
Published in Earth's Future, the study highlights how climate-driven changes, including stronger winter storms and rising sea levels, may increase the importance of healthy dune systems in the years ahead. Protecting and restoring these coastal landscapes could become a key part of future shoreline resilience.