California has lost more than half of its coastal sand dunes over the last 165 years, a new study says.
An estimated 60% of the state’s coastal sand dune systems that were present in the mid-1800s have disappeared due to urban development, land-use changes, and erosion, according to a study conducted by researchers at the University of California, Santa Barbara, and published in the journal Earth’s Future on June 22.
“There are major implications of this loss for the California coast, including reduced habitats for plants, insects and other invertebrates, birds and small mammals,” the paper’s lead author, postdoctoral researcher and physical geographer, Tim Baxter, said in a statement from the university. “Importantly, we also lose coastal protections against storms and sea level rise.”
The study sheds new light on the scale of coastal sand dune loss across the Golden State.
Study’s methodology for tracking dune changes over time
To track the changes in California’s coastal dunes over time, researchers used a combination of historical data and modern technology.
For historical data, researchers looked at topographic survey maps from the mid-1800s to the early 1900s, which provide an early record of coastal environments in the regions, such as beach and dune ecosystems. Researchers reconstructed dune areas by digitizing and georeferencing 140 topographic survey maps, then manually outlined dune habitats.
The research team also mapped present-day dunes (2016) using high-resolution aerial imagery and LiDAR data, with help from a human-guided machine-learning tool (HAML) that identified key features such as the toe and crest, which define a dune’s size, shape, and stability.
By comparing historical and modern maps, researchers quantified how dune areas have changed over time. They also analyzed aerial imagery and land-use data to identify the main drivers of the changes.
Loss varies widely by region, study shows
The extent of coastal dune loss differs significantly across California’s coastline, largely depending on development patterns.
Overall, the study found that the Golden State has lost about 60% of its coastal dune area, going from about 285 square miles in the mid-1800s to about 116 square miles in modern times. Dunes now exist along 22% of the coastline, down from an estimated 33% in the mid-1800s, the study says.
The loss of coastal sand dune systems, however, varies greatly by region, with the greatest losses in areas with dense urban development, the study found.
“The thing that surprised me most was the scale of loss in San Francisco and Los Angeles,” co-author Kyle Emery of UCSB’s Marine Science Institute told the university.
Southern California saw the greatest loss, with about 95% of dunes disappearing, while Central California lost about 60%. Northern California, by contrast, has remained relatively stable, with about a 3% loss.
“Approximately half of what’s left of California’s coastal dune systems are isolated — cut off from coastal processes by infrastructure and transportation networks,” the university said.
Human activity is the main driver of sand dune loss, researchers say
The decline of coastal sand dunes is driven by several factors, including human activity, habitat change, and coastal and river erosion, the study says.
The biggest driver, however, is human activity, “including migration and settlement, which started as early as the Gold Rush (1848), and subsequent development,” the university said.
The team estimates that at least 168 square miles of historical dune ecosystems and about 2 square miles of transitional environments have been lost due to human development, including the expansion of residential communities, industry, and transportation networks, as well as the conversion of dune areas to agricultural land.
Dune loss from development and land-use change is concentrated in Southern and Central California. In Southern California, most losses stem from urban development in the Los Angeles area. In Central California, losses are spread across several regions, including San Francisco, Monterey Bay, Morro Bay, and the Santa Maria Valley.
In Northern California, the biggest driver of dune loss is habitat change, as dunes have been transformed into wetlands, forests or grasslands, accounting for about 3 square miles of loss, the study found.
Statewide, however, losses from habitat change were relatively small, less than 5%, compared with those caused by urban development and infrastructure.
Since the mid-1800s, about 2.7 square miles of dunes have been lost to coastal erosion. In some areas, river erosion has also contributed to losses.
“For instance, it is estimated that the Garcia River in Mendocino County caused the erosion of approximately (0.035 square miles) of the Manchester State Park dunes system,” the study says. “Even greater losses were recorded in other dune systems bordering large rivers in northern California.”
Coastal sand dune loss has also been linked to the creation of waterways for ports, harbors and agriculture, as well as the redirection of rivers, researchers said.
While a small amount of coastal sand dune area was lost to natural processes, “the vast majority of dune loss is the result of human activity, including the development of roads and other infrastructure, agriculture and the introduction of invasive plants,” according to the university.
Decline of sand dunes present challenge for Golden State
The loss poses a growing challenge for California’s coastline, researchers said.
Because coastal dunes help protect communities from flooding, support wildlife and provide many environmental benefits, losing so many of them makes it harder for California to protect its coastline, handle climate change, and meet biodiversity goals, the study says.
Though some large-scale coastal habitat loss and reductions in ecosystem services are irreversible in some cases, researchers said that restoration projects promoting “the development of dynamic coastal dune ecosystems offer a viable adaptation pathway for mitigating climate change impacts and biodiversity loss.”
As some coastal California communities continue to grapple with the impacts of sea level rise, sand dunes have emerged as an appealing restoration strategy, offering sustainable, naturally resilient protection against advancing shorelines, the university said.
However, dunes are not a one-size-fits-all solution, according to the university. Factors such as cost, available space, geographic conditions, and local priorities will ultimately determine whether dunes are a worthwhile option.
This article originally appeared on Palm Springs Desert Sun: Study finds vanishing California dunes raise risk for storms, wildlife
Reporting by Daniella Segura, USA TODAY NETWORK / Palm Springs Desert Sun
USA TODAY Network via Reuters Connect
By Daniella Segura, USA TODAY NETWORK | USA TODAY Network
