California’s Vanishing Sand Dunes Threaten Its Coast

Aerial photos combined with lidar data show the extent of the problem.

California has lost 60% of its coastal sand dunes since the mid-1800s, a new study shows.

In addition to protecting coastal communities from flooding, dunes support a wide range of plants and animals. But they’re also vulnerable. They occupy some of the most favorable land for human development and are also highly threatened by sea level rise.

To protect dunes, scientists need a comprehensive picture of where these ecosystems are located, but existing datasets tend to be incomplete. To get the full picture, Baxter et al. compared historical maps to the current locations of sand dunes to see how their extent and distribution have evolved over time. To find the current locations of sand dunes, the researchers used aerial photographs and lidar data, which they analyzed using a combination of machine learning and manual identification.

California has lost about 442 square kilometers of dunes since the 1850s, which represents about a 60% drop, the researchers found. Dunes that remain have reduced connectivity, making them less favorable as habitat for some species, including federally protected birds like least terns and western snowy plovers. In most cases, those losses occurred because dunes were replaced by human infrastructure such as highways and housing developments. Erosion eliminated others, and invasive grasses further damaged dunes by outcompeting native grasses and hampering restoration efforts.

In some limited cases, dunes actually expanded, usually because of additional sand accumulation on their seaward sides. The researchers estimate that California gained 15.2 square kilometers of new dunes in this way since the 1850s.

But these small gains are not nearly enough to compensate for the large losses sand dunes have experienced over the past 200 years. With winter storms intensifying because of climate change, those losses could soon become problematic for coastal residents, who depend on sand dunes for protection from the sea.

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Source: Earth’s Future, https://doi.org/10.1029/2025EF007790, 2026.

This article originally appeared in EOS Magazine.

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