Most of the world’s population lives on low land near the sea, some of which are predicted to be submerged by the end of the 21st century due to rising sea levels.
The most relevant quantity for assessing the effects of sea-level changes on these communities is relative sea-level rise – the change between the height of the Earth’s surface and the height of the sea’s surface. For an observer standing on the beach, the relative sea-level rise is a net change in sea level, including the rise and fall of the land below the observer’s feet.
Now, using precise measurements from state-of-the-art satellite-based interferometric synthetic aperture radars (InSAR), the ground surface can detect rising and falling with millimeter accuracy, which the Arizona State University research team tracked for the first time is. Vertical land motion of the entire California coast.
They have identified sinking coast local 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 a rapid land subdivision, a high Floods will be at further risk of sea level rise during the projected decades.
“We have ushered in a new era of coastal mapping with more than 1,000 times greater detail and resolution,” said Manochehr Shirazai, the principal investigator of the NASA-funded project. “The unprecedented detail and submillimeter accuracy we solve in our vertical land motion dataset can change the understanding of natural and anthropogenic changes in sea level and related hazards.”
Results were published in this week’s issue Science advance.
The research team consists of M. Blackwell and faculty Manochar Shirajei, Chandrakanta Ojha and Susanna, a graduate student and lead author from ASU School of Earth and Space Exploration (Werth has dual appointment) at ASU School of Earth and Space Exploration (School of Geography and Urban Planning). Worth included.
Em Blackwell had a keen interest in geology, and as soon as Blackwell started graduate school, applications from InSAR attracted him to pursue the project. InSAR uses radar to measure the distance between the satellite and the ground surface, creating highly accurate deformation maps of the Earth’s surface at 10 mm resolution over a spatial limit of 100s km.
Land subdivision may be due to natural and anthropogenic processes or their combination. Natural processes include tectonics, glacial isostatic adjustment, sediment loading, and soil compaction. Anthropogenic causes include groundwater extraction and oil and gas production.
By 2005, approximately 40 million people were exposed to 1 in 100-year coastal flood hazard, and by 2070 the number would increase more than three times. The value of property exposed to floods will increase to approximately 9% of estimated global GDP, with the US, Japan, and the Netherlands being the most at-risk countries. These exposure estimates often depend on estimates of global average sea level rise and do not account for vertical land movements.
The study measured the entire 1350-kilometer long coastline of California from 2007–2018, compiling various satellite images over time, used to create a vertical land motion map with 35 million-pixels at ~ 80 m resolution, A wide range was involved. Coastal uplift and subsistence rates. Policy determinants and general public of coastal communities can freely download data (link in supplementary data).
The four metropolitan areas majorly affected in these areas included San Francisco, Monterey Bay, Los Angeles, and San Diego.
“The rate for most of the San Francisco Bay perimeter is undergoing a 5.9 mm / year,” Blackwell said. “In particular, San Francisco International Airport is shrinking at rates faster than 2.0 mm / year. The Monterrey Bay area, including the city of Santa Cruz, is rapidly sinking without any area of uplift. The sub- Rate rate 8.7 mm /. Year. The Los Angeles area shows sub-zones with small coastal areas, but most of the sub-land is moving inland. “
Areas of land uplift included the San Francisco Bay Area (3 to 5 mm / yr) and north of Central California (same rate).
In the coming decades, due to coastal migration, the coastal population is expected to increase to over 1 billion people by 2050. The risk of future flooding that these communities will face is primarily controlled by the rate of relative sea-level rise, namely, a combination of sea-level rise and vertical land motion. It is important to include the land subsection in regional projections to identify potential flood zones for urban estuaries.
Beyond the study, the ASU research team hopes that others in the scientific community can build on their results to measure and identify coastal threats more widely in the US and around the world.
Study says sea can rise faster than thought
“Tracking California’s sinking coast from space: implications for relative sea-level rise” Science advance (2020). DOI: 10.1126 / Sciadv.aba4551
Provided by Arizona State University
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