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Satellite surveys show California’s coastal hotspots for sinking



Satellite surveys show California’s coastal hotspots for sinking

Coastal elevation in California. Coastal areas, which are defined as those with elevations less than 10 m, are shown in red. Coastal segments with elevations higher than 10 m are colored by a yellow gradient. Credit: USGS NED.

A majority of the world’s population lives in shallow recumbent lands near the sea, some of which are predicted to sink 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 rise in sea level – the change in elevation between surface height. of the Earth and the height of the sea surface. For an observer standing on the shore, a relative rise in sea level is the net change in sea level, which also includes the rise and fall of the land under the feet of an observer.

Now, using accurate measurements from state-of-the-art synthetic satellite-based interferometric aperture (InSAR) radar that can detect the ground and fall with millimeter accuracy, a team of Arizona State University research, for the first time the vertical movement of the entire coastline of California.

They identified local coastal hotspots for sinking, 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 a rapid land subsidy, which will be in higher floods during the decades before the projected rise in sea level.

“We have been in a new era of coastal mapping with more than 1,000 times more detail and higher resolution than ever before,” said Manoochehr Shirzaei, who is the lead investigator of the NASA-funded project. “The unprecedented detail and accuracy of the submillimeter resolved in our vertical movement data 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 Advances in Science.

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 at the School of -Geography and Urban Planning).

Em Blackwell had a keen interest in geology, and as Blackwell started graduate school, InSAR applications attracted them to pursue this project. InSAR uses radar to measure the change in the distance between the satellite and the earth’s surface, and produces highly accurate deformation maps of the Earth’s surface with a resolution of 10s m. over a spatial range of 100s km.

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

Since 2005, about 40 million people have been exposed to a coastal flood risk of 1 in 100 years, and by 2070 this number will more than triple. The value of property exposed to flooding will increase to about 9% of the projected global Gross Domestic Product, with the United States, Japan, and the Netherlands being the countries most exposed. These exposure estimates often rely only on projections of mean sea level rise and do not amount to vertical ground movement.

The study measured the entire 1350-kilometer-long coastline of California from 2007-2018, collected 1000 satellite images over time, used to map the vertical motion of the earth by 35 million million. pixel with a resolution of ~ 80 m, which includes a wide range of coastal uplift and subsidy rates. Policy makers of coastal communities and the general public can download the data freely (link in supplementary data).

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

“The vast majority of the perimeter of St. Francis Bay is undergoing suspension at rates reaching 5.9 mm / year,” Blackwell said. “Notably, San Francisco International Airport is shrinking at rates faster than 2.0 mm / year. The Monterey Bay Area, including the city of Santa Cruz, is rapidly flooding without areas of “Subsidy rates for this area reach 8.7 mm / year. The Los Angeles area shows subsidence with small coastal areas, but much of the luxury is occurring inland.”

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

As we move forward in the coming decades, the coastal population is expected to grow to more than a billion people by 2050, due to coastal migration. The risk of future floods that these communities will face is mainly controlled by the rate of relative sea level rise, that is, the combination of sea level rise and vertical movement. of the land. It is vital to include the land subsidy in regional projections that are used to identify potential flood areas for the urbanized coast.

Beyond the study, the ASU research team hopes that others in the scientific community will be able to build on their results to measure and identify coastal hazards more broadly in the United States and around the world.


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More information:
“Coastal tracking for California sinking from space: Implications for a relative rise in sea level” Advances in Science (2020). DOI: 10.1126 / sciadv.aba4551

Provided by Arizona State University



Citation: Satellite survey shows California sinking coastal hotspots (2020, July 31) found on July 31, 2020 from https://phys.org/news/2020-07-satellite-survey -california-coastal-hotspots.html

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