Tracking California’s Sinking Coast From Space: San Francisco, Monterey Bay, Los Angeles, and San Diego Majorly Affected

Sinking California Coasts

Coastal elevation in California. Coastal zones, which are defined to be those with elevations less than 10 m, are shown in red. Segments of the coast with elevations higher than 10 m are colored by a yellow gradient. Credit: USGS NED

A majority of the world population lives on low lying lands near the sea, some of which are predicted to submerge by the end of the 21st century due to rising sea levels.

The most relevant quantity for assessing the impacts of sea-level change on these communities is the relative sea-level rise — the elevation change between the Earth’s surface height and sea surface height. For an observer standing on the coastland, relative sea-level rise is the net change in the sea level, which also includes the rise and fall of the land beneath observer’s feet.

Now, using precise measurements from state-of-the-art satellite-based interferometric synthetic aperture radar (InSAR) that can detect the land surface rise and fall with millimeter accuracy, an Arizona State University research team has, for the first time, tracked the entire California coast’s vertical land motion.

They’ve identified local hotspots of the sinking coast, in the cities of San Diego, Los Angeles, Santa Cruz, and San Francisco, with a combined population of 4 to 8 million people exposed to rapid land subsidence, who will be at a higher flooding risk during the decades ahead of projected sea-level rise.

“We have ushered in a new era of coastal mapping at greater than 1,000 fold higher detail and resolution than ever before,” said Manoochehr Shirzaei, who is the principal investigator of the NASA-funded project. “The unprecedented detail and submillimeter accuracy resolved in our vertical land motion dataset can transform the understanding of natural and anthropogenic changes in relative sea-level and associated hazards.”

The results were published in this week’s issue of Science Advances.

The research team included graduate student and lead author Em Blackwell, and faculty Manoochehr Shirzaei, Chandrakanta Ojha, and Susanna Werth, all from the ASU School of Earth and Space Exploration (Werth has a dual appointment in the School of Geography and Urban Planning).

Em Blackwell had a keen interest in geology, and as Blackwell began graduate school, the applications of InSAR drew them to pursue this project. InSAR uses radar to measure the change in distance between the satellite and ground surface, producing highly accurate deformation maps of the Earth’s surface at 10s m resolution over 100s km spatial extent.

Land subsidence can occur due to natural and anthropogenic processes or a combination of them. The natural processes comprise tectonics, glacial isostatic adjustment, sediment loading, and soil compaction. The anthropogenic causes include groundwater extraction and oil and gas production.

As of 2005, approximately 40 million people were exposed to a 1 in 100-year coastal flooding hazard, and by 2070 this number will grow more than threefold. The value of property exposed to flooding will increase to about 9% of the projected global Gross Domestic Product, with the U.S., Japan, and the Netherlands being the countries with the most exposure. These exposure estimates often rely only on projections of global average sea level rise and do not account for vertical land motion.

The study measured the entire 1350-kilometer long coast of California from 2007-2018, compiling 1000s of satellite images over time, used for making a vertical land motion map with 35-million-pixel at ~80 m resolution, comprising a wide range of coastal uplift and subsidence rates. Coastal communities’ policymakers and the general public can freely download the data (link in supplemental data).

The four metropolitan areas majorly affected in these areas included San Francisco, Monterey Bay, Los Angeles, and San Diego.

“The vast majority of the San Francisco Bay perimeter is undergoing subsidence with rates reaching 5.9 mm/year,” said Blackwell. “Notably, the San Francisco International Airport is subsiding with rates faster than 2.0 mm/year. The Monterey Bay Area, including the city of Santa Cruz, is rapidly sinking without any zones of uplift. Rates of subsidence for this area reach 8.7 mm/year. The Los Angeles area shows subsidence along small coastal zones, but most of the subsidence is occurring inland.”

Areas of land uplift included north of the San Francisco Bay Area (3 to 5 mm/year) and Central California (same rate).

Going forward in the decades ahead, the coastal population is expected to grow to over 1 billion people by 2050, due to coastward migration. The future flood risk that these communities will face is mainly controlled by the rate of relative sea-level rise, namely, the combination of sea-level rise and vertical land motion. It is vital to include land subsidence into regional projections that are used to identify areas of potential flooding for the urbanized coast.

Beyond the study, the ASU research team is hopeful that others in the scientific community can build on their results to measure and identify coastal hazards more broadly in the U.S. and around the world.

Reference: “Tracking California’s sinking coast from space: Implications for relative sea-level rise” by Em Blackwell, Manoochehr Shirzaei, Chandrakanta Ojha and Susanna Werth, 31 July 2020, Science Advances.
DOI: 10.1126/sciadv.aba4551

9 Comments on "Tracking California’s Sinking Coast From Space: San Francisco, Monterey Bay, Los Angeles, and San Diego Majorly Affected"

    Water. Weight. Gravity. Slabs of humongous rocks assembled together to form Earth. Earthquakes. Global warming. More water. More gravity. More quakes that are also more serious. What happens when the North and South Pole melt in about 15-25 years? Can anyone out there please answer this? NASA? Anyone? has something to say about this that all of you should read because all hell is going to break out on Earth in about 20-30 years as the Earth takes a very quick spin into a whole new climate era that will very quickly lead to a weather pattern that will lead to the death of this planet! I’m warning you! You better all wake up and save this planet or you can all kiss your butts goodbye because in 20-30 years you all will be fighting for your lives as you try to survive on a planet that will be daily cooked by the Sun and all water will evaporate, in land first and then the oceans. On that facebook page is why global warming is happening and how to stop it. More info is being added periodically.

  2. I’ve lived from LA county all the way down by the border with Mexico and have literally worked right on the coast for over twenty years. In all of this time, and surely decades before, there have been countless reports of California sinking due to global warming. I’ve kept personal detailed observation of the waterline and to my surprise it seems as though the water is doing the opposite of what is being reported by scientists around the globe. The water used to smash against rocks and splash over 30 feet in the air occasionally getting me wet, that hasn’t been the case in over eight years. I wonder if any of these so called scientists actually ever set foot on any California beaches. I’ve witnessed the water line recede in Mission Bay and Beach in San Diego, San Clemente, San Pedro, Santa Monica, and as far north as Morro Bay. There isn’t an article by any scientist that will prove to me different than what I’ve observed with my own two eyes.

  3. Mario’s eyes vs a ASU’s research dept and NASA using instruments with millimeter accuracy and a decade worth of data. Tough call.

  4. Nick J Monroe | August 5, 2020 at 2:25 am | Reply

    Mario,wake up and smell the coffee pal!
    Your reasoning is so flawed and lacking of any type of reliable data. Do you think your eyes have better vision then a satellite in space?
    If you don’t know the answer to that question, you have far bigger problems than global warming.
    Smh lol.

  5. Bill Wooginowski | August 5, 2020 at 7:08 am | Reply

    The north pole melting will have no impact what so ever. Put some ice cube in a glass of water and let them melt. The level I the glass doesn’t change. The polar ice cap in the north is just ice sitting in water.

  6. ChickenLittle | August 5, 2020 at 1:29 pm | Reply

    “What happens when the North and South Pole melt in about 15-25 years? Can anyone out there please answer this?”
    That should be the least of your worries. It will still be hard floating water. AKA ice.

  7. So if I put ice in a full glass of water, it won’t over flow? ..and when it melts would be the same amount. Got it👍 I was worried there for a moment LOL

  8. They have been saying Calif has been falling in the ocean for 60years.of my life.same old story. But it’s coming out of the ocean.its just like the old story at lakes catfish as big as vw bugs.eyes like car lights.or the old story of bigfoot.just all b.s.

  9. “in 20-30 years you all will be fighting for your lives as you try to survive on a planet that will be daily cooked by the Sun and all water will evaporate…”

    Parody, right? … right?

    Catastrophe is always 20-30 years away, since at least St. Luke. … The actual rate of warming since 1979, the beginning of satellite measurements, has been ~1.5C per century, which if it persists will take us back to the global average temp at the peak of the last interglacial warming period (when catastrophe failed to ensue). Boiling off the oceans could be accomplished in 1,000 years, but you’d need to trap all incoming solar radiation and accumulate it at the surface to do that. Meanwhile, the Milankovitch cycle which largely governs our climate will be trending cooler for the next 1,000 years. Be grateful for the warmth.

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