Not only are rising sea levels a concern – they are also slowly declining under the pressure of their own development, according to a new study, which underlines the importance of influencing models of climate change risk.
Geologist Tom Parsons, of the United States Geological Survey (USGS), looked at San Francisco as a case study of how major urban developments could affect and lower the Earth’s surface.
With its numbers, San Francisco could have sunk as much as 80 millimeters (3.1 inches) as the city has grown over time. Assuming that the Bay Area is at risk of sea level rise of as much as 300 mm (11.8 inches) by 2050, the additional variability added by slow growth is important enough to be anxious.
“As global numbers move unevenly towards the coasts, this further forecast combined with the expected rise in sea level could pose the associated risk. to exacerbate dehydration, ”Parsons wrote in his paper.
Taking into account a list of all the buildings in the city and their contents, the study calculated the weight of San Francisco (population: 7.75 million) as about 1.6 trillion kilograms – about 3.5 trillion pounds, or approximately 8.7 million Boeing 747s.
That could be enough for both the real lithosphere on which the urban center bends, and perhaps more importantly, altering reasonable levels of fissure blocks – the floating rocky fragments that it makes up the Earth’s surface.
The 80 mm slope seems to be a maintenance estimate, as the weight calculation did not include objects outside buildings – including transport infrastructure, vehicles. or people. The same species appears to be declining in other parts of the world, although it is largely dependent on the geology of the area.
“The unique results found for the San Francisco Bay Area are likely to apply to any major urban center, but with a different weighting,” Parsons wrote.
“The effects of anthropogenic loading at tectonically active continental margins are more likely than in more stable continental interiors where the lithosphere tends to be thicker and harder.”
There are plenty of other reasons for courtship to think about as well, including the movement of a tectonic plate and the pumping of groundwater necessary to support a growing population – something we seen causing a city to sink in other parts of the world.
Although this current study only looked at San Francisco, and made some broad assumptions about modeling, the findings are well-known enough to bring the weight of a city to another attention when scientists find out how geography may change over time, and which areas are at risk as sea levels rise.
There is still enough information to dig it in, especially in cities that are already at risk from aches. Sediment and rainwater systems under San Francisco International Airport on the coast – the heaviest building in the city – have already been congested causing 4 mm (0.16 inches) of annual subsidence.
“It should be possible to improve the techniques presented here by using satellite or aerial imagery to perform more detailed analyzes in similar flood zones,” Parsons wrote.
“Such detailed analyzes may provide better insights into changes in subsurface porosity changes and resulting flow rates.”
The research was published in AGU Advances.