MAY 26, 2022 4:30 PM PDT

Its All Downhill From Here - Why Coastal Cities Around the World are Sinking

WRITTEN BY: Mandy Woods

It is no secret that some coastlines have seen extreme change over the last several thousand years of human existence. We can see the literal human footprint of this change thanks to today's innovative satellite technology. As the human population increases, it leads to greater use of, and influence on, the environment around us.

Scientist Matt Wei of the University of Rhode Island, and his colleagues, have carried out a study including 99 coastal cities from 6 continents. It is one of the only studies to include this scale of global data.

Most of the teams' observations were made between 2015 and 2020 through two main satellites. The use of microwave signals, the measuring of timing and intensity of their signal bounce-back, determined the height of the ground with accuracy within millimeters throughout this period.

The data in question? With both satellites being in a polar orbit, researchers could get the same data every twelve days to trace deformation over time. Patterns of subsidence showed a rate of at least 5 centimeters a year, primarily within cities like Tianjin in China; Karachi in Pakistan; and Manila in the Philippines. While previous studies' data were limited to one region or city, this time, the study was so geographically different that it revealed a spatiotemporal correlation between events across the globe.

Subsidence is the sinking of the ground surface due to the movement of underground material. Mostly caused by the continuous removal of water, oil, natural gas, and mineral resources. In many of the sinking cities, the areas have been commercially and residentially developed.

Jakarta, Indonesia, was the location of one of the previous studies, and it showed a strong correlation between land subsidence and the surrounding developed urban landscape. Within the Jakarta Basin, four main types of subsidence can be found, and all are heavily impactful. From subsidence due to groundwater extraction, loads of construction, and subsidence from the natural consolidation of alluvial soils and tectonic subsidence, the rates across the area span from 1-15 centimeters a year. The data for this study started in 1982 and ended in 2010.

Out of the 99 cities examined in the more recent study, 33 were reported to see portions of the city sinking around 10 millimeters or more. These cities were in Europe, North America, Africa, and Australia. In Florida, for example, the north shore of Tampa Bay observed 6 millimeters a year of subsidence throughout the study.

The area of subsidence within Tampa Bay consists primarily of groundwater aquifers, sources of freshwater for surrounding areas, suggestive of groundwater extraction as the main reason it is "sinking."

Other scientists have noticed patterns of other environmental change that coincide with these events as well: global warming & coastal flooding. While we see coastal lines sinking due to subsidence, the planet is also met with rising temperatures and sea levels in tandem. This study indicates some coasts are sinking quicker than sea levels are rising. Careful monitoring and policy intervention are one-way humans can start to minimize future problems and their consequences.

Sources: AGUPubs, Science News, Springer, National Ocean Service

About the Author
BA in Anthropology
Mandy (She/Her) is a Scientific Writer and an active Field Archaeologist. She has worked in the Southwest, Midwest, and Great Basin for Historical Archaeology and Resource Management. She received her B.A. from the University of New Mexico with a focus in Archaeology and History. In her free time, she is outdoors with her two dogs, Nala and Nova. She channels her passion for nature and exploration into her career.
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