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Satellite surveys show the sinking of California coastal hot spots



Satellite surveys show the sinking of California coastal hot spots

Coastal rise in California. Coastal zones, defined as those with a height of less than 10 m, are shown in red. Coastal segments with heights higher than 10 m are colored by a yellow gradient. Credit: USGS NED.

Most of the world’s population lives on low-lying land near the sea, some of which are predicted to collapse by the end of the 21st century due to rising sea levels.


The most relevant volume for assessing the effects of sea level change on these communities is the rising sea level — the rising elevation between the surface of the Earth and the surface of the sea. For an observer standing on the shore, the relative increase in sea level is the net change at sea level, which also includes the rise and fall of land under the observer’s feet.

Now, using accurate measurements from state-of-the-art satellite-based interferometric synthetic aperture radar (InSAR) that can detect ground rise and fall with millimeter accuracy, an Arizona State research team The University has, for the first time, monitored the entire land movement along the California coast.

They identified local coastal hotspots, 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 flooding, which would be increased flooding risk in the decades ahead of the expected sea level rise.

“We have begun a new era of coastal mapping with more than 1,000 higher details and resolutions than ever before,” said Manoochehr Shirzaei, who is the chief investigator of the NASA-funded project. “The unprecedented detail and submillimeter accuracy resolved in our vertical ground motion can alter the understanding of natural and anthropogenic changes at relative sea level and related hazards.”

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

The research team included graduate student and leading author Em Blackwell, and faculty Manoochehr Shirzaei, Chandrakanta Ojha and Susanna Werth, all from the ASU School of Earth and Space Exploration (Werth with an appointment at School of Geography and City Planning).

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

Landslides can occur due to natural and anthropogenous processes or a combination of these. Natural processes consist of tectonics, glacial isteratic adjustment, sediment loading, and soil compaction. Anthropogenic causes include groundwater extraction and oil and gas production.

In 2005, approximately 40 million people were exposed to a 1 in 100-year coastal flood risk, and by 2070 this number will more than triple. The value of property exposed to flooding will increase to almost 9% of the expected global Gross Domestic Product, with the US, Japan, and the Netherlands being the countries with the most exposure. Estimates of this exposure often rely solely on the expectations of the global average sea level rise and do not account for vertical land motion.

The study measures the entire 1350-kilometer-long coastline of California from 2007-2018, combining about 1000 satellite images over time, used for creating a vertical ground motion path with 35-million-pixels at ~ 80 m resolution, consisting of a wide range of coastal rise and subsidence rate. Baybayin community policy developers and the general public are free to download the data (link to supplementary data).

The four metropolitan areas most affected by these areas include San Francisco, Monterey Bay, Los Angeles, and San Diego.

“Most of the San Francisco Bay perimeter is subject to subsidence with rates reaching 5.9 mm / year,” Blackwell said. “Interestingly, the San Francisco International Airport is declining with rates faster than 2.0 mm / year. The Monterey Bay Area, including the city of Santa Cruz, is sinking rapidly without any increase zones. Subsidence rates for this area reach 8.7 mm / year. The Los Angeles area shows subsidence along small coastal areas, but most subsidence occurs on land. “

Landfills include the northern San Francisco Bay Area (3 to 5 mm / year) and Central California (same rate).

Going forward in the coming decades, the coastal population is expected to grow to more than 1 billion people by 2050, due to shoreline migration. The future flood risk that these communities will face is largely controlled by the relative rate of sea level rise, in particular, the combination of sea level rise and vertical land movement. It is important to include land subsidence in regional projections used to identify areas of potential flooding for urbanized coastline.

Beyond the study, the ASU research team hopes that others in the scientific community can come up with their results to measure and identify coastal hazards more widely in the US and around the world.


The study said the sea could rise faster than previously thought


Additional information:
“Monitoring the sinking of the California coast from outer space: Implications for relative sea level rise” Advancing Science (2020). DOI: 10.1126 / sciadv.aba4551

Provided by Arizona State University

Mention: Satellite survey shows sinking of California coastal hot spots (2020, July 31) obtained July 31, 2020 from https://phys.org/news/2020-07-satellite-survey-california- coastal-hotspots.html

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