Sea Level Rise

The Humboldt Bay area is experiencing the fastest rate of relative sea level rise on the West Coast. That's because tectonic activity is causing the ground beneath the bay to sink at the same rate that the ocean is rising. According to the California Ocean Protection Council's 2024 Science & Policy Update, sea level in the Humboldt Bay area is expected to rise approximately 1.5-2 feet above 2000 levels by 2060 and 3.9-5.5 feet by 2100. 
The primary impacts from sea level rise are increases in flooding, erosion, and rising groundwater. Sea level rise will expand areas vulnerable to flooding during major storms, as well as in the rare but catastrophic event of a major tsunami. The term 100-year flood is used as a standard for planning, insurance, and environmental analysis. But these extreme storms are happening with increasing frequency, in part due to rising seas. Sea level rise will cause more frequent—and more damaging—floods to those already at risk and will increase the size of the coastal floodplain, placing new areas at risk to flooding.
To view sea level rise scenarios for the Humboldt Bay area, visit NOAA's 2022 Sea Level Rise Viewer and go to the local scenario for the North Spit.     

Interactive Map of King Tide Photos

The California Coastal Commission's King Tide Photo Project features photos from the Humboldt Bay area and across the state. Anyone can upload photos online or via a smartphone app.

Click HERE to upload yours.

Left: Erosion along New Navy Base Road in Samoa during the December 23-24, 2022 King Tides. Photo by Jen Kalt.

The edges of Humboldt Bay are on the verge of being overrun by the sea. It laps at the boundaries of Highway 101, surrounds the Arcata Marsh, and sneaks around the corners of low-lying industrial areas in Eureka. 

SINKING SHORELINE

Humboldt’s location at the end of the Cascadia Subduction Zone makes the area more vulnerable to sea level rise than any other location on the California coast. Due to its position in a very active tectonic area and the specific activity of the surrounding plates, the Humboldt County region is steadily sinking, or subsiding. 

The Humboldt Bay Vertical Reference System Working Group is a research group focused on identifying geology’s role in Humboldt Bay sea level rise. In a 2017 report, they found that land subsidence contributes to sea level rise 2 to 3 times more in Humboldt County than anywhere else in California. Of the 18 inch rise in sea levels that has occurred locally in the past century, an estimated 50% is due to tectonic subsidence.

“The ocean isn’t rising any faster off of our coast than it is down in San Francisco, but we have subsidence that the rest of California doesn’t have,” said environmental planning consultant Aldaron Laird. 

The county is planning on mitigating the risks of sea level rise along a particularly vulnerable stretch of Highway 101 between Eureka and Arcata by restoring salt marsh.
Restoring about 17 acres of salt marsh along a 1.25-mile stretch of Highway 101 between Brainard and Bracut would reduce the risk of flooding and the erosion of the shoreline for at least a century, Humboldt County Public Works Deputy Director Hank Seemann told the commissioners of the Humboldt Bay Harbor, Recreation and Conservation District on Thursday.
“If sea level rise continues to accelerate, there would be some point in the future where the salt marsh could get flooded out, but our study concluded it would likely have benefits for several decades,” Seemann said.
The Humboldt Bay Natural Shoreline Infrastructure Feasibility Study, which was completed in September, illustrated the most feasible designs and what the shoreline is expected to look like once the project is complete.
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Sea level is rising more rapidly in the Humboldt Bay region than in any other place on the US West Coast. Cal Poly Humboldt’s Center for Sea Level Rise has been looking at the implications and last Monday, the San Francisco Chronicle gave us feature treatment.Sea level is rising more rapidly in the Humboldt Bay region than in any other place on the US West Coast. Cal Poly Humboldt’s Center for Sea Level Rise has been looking at the implications and last Monday, the San Francisco Chronicle gave us feature treatment.
Sea level rise became news in the 1970s. Studies were published and in 1988 the UN formed the Intergovernmental Panel on Climate Change was formed. Since 1993, satellite altimetry has provided a global picture of the rising oceans. The current estimate of average sea level rise is 3.4 millimeters (.13 inches) per year. There is no gray area here, it is a measured fact.
But the ocean isn’t a bathtub, and the rise is not uniform, rising more rapidly in some areas and dropping in others. How water level changes locally is a function of many variables. The three most important are thermal expansion, the supply of water, and deformation of the sea floor.
Water expands as it warms. A warmer ocean raises sea level with no additional water. Expansion rates are complex and depend on salinity, temperature, and pressure. There are seasonal changes and longer ones. Thermal expansion in strong El Niño years can raise the background tide levels by nearly a foot.

Anchored by the cities of Eureka and Arcata and known for its redwood forests, cannabis tourism and cool, misty beaches, Humboldt Bay also has an unwelcome distinction: It has the fastest rate of sea level rise on the West Coast.
Tectonic activity is causing the area around the bay roughly 300 miles north of San Francisco to sink, which gives it a rate of sea level rise that is about twice the state average. Compared to 2000, the sea in the area is expected to rise 1 foot by 2030, 2.3 feet by 2050 and 3.1 feet by 2060, according to California Ocean Protection Council.
Residential areas, wastewater treatment plants and a segment of Highway 101 that connects Eureka and Arcata are all at risk — especially when the frequent and intense storms associated with climate change trigger more flooding. There are even long-term worries about a nuclear waste storage facility on the bluffs. Yet the region also has become a test case for how to adapt to a problem that faces all of coastal California, including by restoring wetlands that were filled in for logging and farming in earlier eras.
“We say the bay is going to take back from us what we borrowed for the last hundred years or so,” said Jennifer Kalt, director of the nonprofit group Humboldt Baykeeper and a member of the Cal Poly Humboldt Sea Level Rise Institute.
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New York City is vulnerable to rising seas and larger, more powerful storms that result in more frequent and intense flooding and what was once a 500-year flood prior to human-induced climate change now occurs on average once every 24 years. This is according to a study published in the Proceedings of the National Academy of Sciences.
“Flood heights are increasing and have increased since the pre-anthropogenic era, not only because of rising sea levels but also because of the impact that climate change is having on tropical cyclones,” said lead author Andra Reed of Penn State University.
Reed and colleagues made their conclusions based on climate models that simulated tropical storms and subsequent flooding for the region beginning in 850. They found that average flood height increased by more than 4 feet from 850 to 2005.
When Hurricane Sandy hit New York in 2012, it caused an estimated $50 billion in damage and destroyed at least 650,000 houses. Prior to 1800, such a flood could be expected to hit the city every 3,000 years. Today, a flood of that magnitude will occur on average every 130 years, Reed said. 
“Our planning is not designed to look forward,” said Melanie Gall, a University of South Carolina professor who studies disaster risk and emergency management. “When you look at flood insurance or how flood zones are mapped, it is always based on past events. It never looks at how storm surge will change in the future. There needs to be more proactive planning.”
Continuing development in New York and other coastal areas is also making the impact of such floods worse, similar to how water in a bathtub rises when displaced by a person entering the tub.
“The area that will be affected is larger because there is more development,” Gall said.
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More Articles …

  1. 44 Feet: The de-facto nuclear waste site on the edge of Humboldt Bay and one group's efforts toward an atomic-ally correct future
  2. The Sea Also Rises: Humboldt County Grand Jury Report on Sea Level Rise 
  3. It’s time to start planning for sea level rise, says Humboldt County grand jury
  4. Crucial Antarctic Glacier Likely to Collapse Much Earlier than Expected

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