Most of the world’s population lives in lowlands near the sea, some of which are expected to sink by the end of the 21st century due to rising sea levels.
The most relevant measure for assessing the impacts of sea level change on these communities is the relative rise in sea level — the change in elevation between the Earth’s surface height and sea surface height. For an observer lying on the shore, the relative rise in sea level is the net change in sea level, which also includes the rise and fall of the earth beneath the observer’s feet.
Now, using accurate measurements of state-of-the-art satellite-based synthetic interferometric aperture (InSAR) radar, which can detect the rise and fall of the earth’s surface with millimeter accuracy, a research team from the University of Arizona has tracked for the first time. all the vertical movement of the California coast.
They have identified points of local origin 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, which they will have a higher flood. risk during the decades prior to the expected sea level rise.
“We have created a new era of coastal mapping with more than 1,000 times more detail and resolution than ever before,” said Manoochehr Shirzaei, who is the lead researcher on the NASA-funded project. “The unprecedented detail and accuracy of the submillimeter solved in our vertical ground motion dataset can transform the understanding of natural and anthropogenic changes in relative sea level and associated risks.”
The results were published in this week ‘s issue of Scientific advances.
The research team included graduate student and lead author Me Blackwell, and professors Manoochehr Shirzaei, Chandrakanta Ojha and Susanna Werth, all of the ASU School of Earth and Space Exploration (Werth has a double appointment at the School of Geography and Urbanism).
Me Blackwell had a keen interest in geology and when Blackwell started graduate school, InSAR applications attracted them to continue this project. InSAR uses radar to measure the change in distance between the satellite and the earth’s surface, producing highly accurate deformation maps of the earth’s surface at a resolution of 10s m over a spatial extent of 100 km.
Soil subsidence can occur due to natural and anthropogenic processes or a combination of these. Natural processes include tectonics, glacial isostatic adjustment, sediment loading, and soil compaction. Anthropogenic causes include groundwater extraction and oil and gas production.
As of 2005, approximately 40 million people were at risk of coastal flooding every ten years, and by 2070 that number will grow by more than three. The value of property exposed to floods will increase to approximately 9% of projected global gross domestic product, with the United States, Japan and the Netherlands being the countries with the most exposure. These exposure estimates are often based solely on projections of rising global mean sea levels and do not take into account vertical land movements.
The study measured the entire 1350-mile coastline of California between 2007-2018 and collected thousands of satellite images over time, used to make a 35 million-pixel vertical ground map. at a resolution of ~ 80 m, comprising a wide range of coastal elevation and subsidence rates. Those responsible for coastal communities and the general public can download the data for free (link in supplementary data).
The four metropolitan areas affected mostly in these areas included San Francisco, Monterey Bay, Los Angeles and San Diego.
“The vast majority of the perimeter of San Francisco Bay is undergoing with rates reaching 5.9 mm / year,” Blackwell said. “Mostly, San Francisco International Airport is shrinking at faster rates of 2.0 mm / year. The Monterey Bay area, including the city of Santa Cruz, is rapidly sinking without areas of “The subsidence rates in this area are 8.7 mm / year. The Los Angeles area shows subsidence along small coastal areas, but most of the subsidence occurs inland.”
The land elevation areas included north of the San Francisco Bay Area (3 to 5 mm / year) and Central California (same rate).
Over the next few decades, the coastal population is expected to grow to more than 1 billion people by 2050, due to coastal migration. The future flood risk that these communities will face is mainly controlled by the relative rate of sea level rise, i.e. the combination of sea level rise and vertical land movement. It is critical to include land subsidence in regional projections that are used to identify potential flood zones of the urbanized coastline.
Beyond the study, the ASU research team hopes other people in the scientific community can leverage their findings to measure and identify coastal risks more widely in the U.S. and around the world.
The study says the seas may be rising faster than previously thought
“Tracking California’s Sinking Coast from Space: Implications for Relative Sea Level Rise” Scientific advances (2020). DOI: 10.1126 / sciadv.aba4551
Provided by Arizona State University
Citation: Satellite Survey Shows California Coastal Landmarks (2020, July 31) Retrieved July 31, 2020 at https://phys.org/news/2020-07-satellite-survey-california -coastal-hotspots.html
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