Cities around the world are slowly sinking, and it is not just the rising sea levels that they should be worried about. Their colossal weight is also to blame, recent research found, emphasizing the importance of including subsidence into models of climate change.
According to an article in ESKP, Jakarta was 15 centimeters higher last year than they are now. One reason why they are slowly sinking lies in the enormous groundwater being bumped on the surface that alters the pressure balances underground.
This could occur unnoticed and may happen rapidly, especially in megacities located in river deltas or near the coast. It could be that this could sink a city by up to 30 centimeters a year at extreme rates.
Worsening Case of City Sinking
Tom Parsons, a geophysicist from the United States Geological Service (USGS) agency, takes San Francisco as a case study of how cities could be slowly sinking. His calculations showed that the city might have sunk as much as 80 millimeters or 3.1 inches as the city continue to progress, ScienceAlert reported.
It is estimated that the Bay Area could be under threat from the sea level rise of about 300 millimeters (11.8 inches) by 2050, plus the slow subsidence.
"As global populations move disproportionately toward the coasts, this additional subsidence in combination with expected sea-level rise may exacerbate risk associated with inundation," Parsons wrote.
In addition to that is the inventory of contents that the buildings of cities have, and the population of about 7.75 million, which approximately sums up to 1.6 trillion kilograms (3.5 trillion pounds) or about as heavy as 8.7 million Boeing 747s.
Technically speaking, that weight is enough to bend the lithosphere on which cities sit, or perhaps even more to change the relative levels of floating chunks of rock that make up the Earth's surface.
But the 80 millimeters is just a rough estimation as it does not include the weight of the things outside the buildings, like transportation infrastructure, vehicles, and people. It is believed that the same scenario is likely to happen as well in other cities of the world, Parsons said.
Other Causes of Subsidence
Other causes of subsidence should also be considered. These include the shifting of tectonic plates and the groundwater pumping necessary to support the city's growing population, seen in other countries as significant factors that contribute to city sinking.
Moreover, the study's findings also consider how geography might change over time and which areas are under threat the sea levels begin to get higher.
ESKP identified some processes that could influence land subsidence. These are extraction of groundwater or oil, the weight of structures, vibration, and compaction caused by traffic, underground infrastructure, dikes, or levees that hinder sediment deposition.
Moreover, it also listed some cities under threat of subsidence, such as Shanghai in China, Bangkok in Thailand, Jakarta in Indonesia, and New Orleans in the US.
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