What do you understand by Sinking cities?
1. What do you understand by Sinking cities? Give example and discuss (150 words)
2. What issues have been raised in the video related to London? (220 words) List at least 3 and discuss.
3. What has been done to improve the situation in London? (100 words)
4. List 5 keywords from the video.
Watch the video on LONDON https://video.alexanderstreet.com/watch/london-5/details?context=channel:public-broadcasting-service-pbs Links to an external site.
or https://www.pbs.org/wnet/peril-and-promise/video/watching-sinking-cities-london/Links to an external site.
While sea level rise seems increasingly inevitable, a separate but more solvable problem faces many of the world’s coastal cities: how to stop their gradual sinking into the ground.
Subsidence, or the gradual sinking of landscapes under their own weight, has long been associated with agricultural areas.
Years of pumping groundwater for irrigation caused parts of California’s San Joachin Valley to sink by nine metres in the space of 50 years during the twentieth century, according to the United States Geological Survey (USGS).
“The main cause of subsidence, in general, in the world, not even in cities, is lowering the groundwater table,” says Herbert Einstein, a professor of rock mechanics at the Massachusetts Institute of Technology (MIT).
However, a separate type of subsidence gave residents of San Francisco’s Millennium Tower a very different kind of sinking feeling, after the northwestern corner of the luxury high rise sank by more than 40 centimetres over the course of a decade.
According to Tom Parsons, a research geophysicist at the USGS, buildings like the Millennium Tower may be causing the entire city to sink, exacerbating the impacts of climate change-induced sea-level rise.
Parsons found general ranges of subsidence to be between five and 80 millimetres in the San Francisco Bay Area, with the most subsidence recorded around San Francisco International Airport, the region’s heaviest building.
He attributed this to the rapid increase in the mass of these buildings and its effect on the earth underneath.
“There’s the additional weight and then there’s the ability of the water underneath that is allowed to flow away,” says Jaap Nienhuis, a geomorphologist at Utrecht University who studies coastal subsidence. “If the water is allowed to flow away, then you suddenly have excess space, which can cause the land to sink.”
Parsons warns this problem will likely be worse in the developing world as more people migrate to coastal cities.
The Flanders Marine Institute, a non-profit organisation, estimates that 60 percent of the world’s population already lives in coastal areas, with an additional 65 percent of the world’s most populated cities also located on the coast. The United Nations expects these figures to rise, along with sea levels.
“In a lot of countries it is considered a very big issue,” says Nienhuis. “It is important and needs to be highlighted more, definitely in comparison to climate change-driven sea-level rise.”
Perhaps the most prominent example of where urbanization-driven subsidence is exacerbating the impacts of sea-level rise is Jakarta, the capital of Indonesia.
Jakarta is sinking faster than any other major city in the world, mostly as a result of groundwater being pumped out faster than it can be replenished. An estimated 40 percent of the city is already below sea level.
Nienhuis believes that cities such as Jakarta exemplify why increased awareness should be given to subsidence.
“Subsidence is easier to manage [than sea level rise] because it is a local problem and in many cases is also much bigger,” he says. “In cities like Jakarta, you are going to have tens of centimetres of subsidence each year, whereas sea level rises only a couple of millimetres per year, so that’s a factor difference of 10 or more.”