Subsidence

This week we talk about the raising of Chicago, Jakarta, and sea level rise.

We also discuss groundwater, flooding, and insurance.

Recommended Book: Once Upon a Tome by Oliver Darkshire

Transcript

In the mid-19th century, the city of Chicago, its many sidewalks and buildings and other infrastructure, were hoisted using jackscrews, which are kind of like heavy-duty versions of the jacks you might use to lift your car to replace a tire.

The impetus for this undertaking, which was substantial and paid for with a combination of city and private funds, was Chicago's persistent drainage issues: the city was located at about the same altitude as neighboring Lake Michigan, and the ground upon which it was constructed was consequently pretty swampy to begin with, but became even more so as all those sidewalks and buildings and other human-made environmental objects were installed, putting downward pressure on that swampy soil, which led to widespread and persistent pools of standing water throughout the city.

All this standing water led to the spread of diseases like dysentery and typhoid fever—the sorts of issues that tend to arise when there's opportunity for pathogenic beasties to hang out and spread and come into contact with drinking water sources, not to mention essentially every surface in a city, and in 1854 there was an outbreak of cholera—which is also caused by bacteria getting into peoples' bodies, usually from infected water sources—that killed about 6% of Chicago's total population.

So this was an area that was already prone to what's called subsidence—the sinking of land that can be both natural and sparked or amplified by human activity in various ways—and Chicago's development into a city sped up that process, causing it to sink even further, quite rapidly, and that led to a collection of mostly but not exclusively water-related issues, which at this moment in history, the mid-19th century, meant a lot of disease-spread due to insufficient water sanitation efforts and infrastructure, and a very hit-or-miss understanding of the mechanisms of the diseases that were carried by that insufficiently treated water.

The first brick building to be hoisted in this way was elevated in January of 1858 and required about 200 jackscrews to lift it six feet and 2 inches higher than its previous altitude, and that kicked-off a period of remarkably rapid and successful elevations throughout the city, including all sorts of huge, heavy, at times quite wide and cumbersome buildings of all heights and material composition, installing elements of the city's new sewage systems around the existing buildings, then covering all that up with soil, pouring or reinstalling roads and sidewalks atop that soil at the new height, and then raising all the buildings, filling the space beneath them with soil as they were slowly cranked up to that new baseline.

This wasn't a straightforward effort, and there were several false-starts, initial problems that had to be solved, and quite a few pieces of the old city that either couldn't be elevated, and thus had to be buried and rebuilt, or that were moved to new locations, placed on rollers and shifted to areas, mostly on the outskirts of the city, which kept them aloft without having to raise them using the jackscrew method.

Interestingly, some of the elevated buildings, like the Tremont House hotel, continued to function even as they were raised; guests continued to frequent the hotel, and some of them apparently didn't even realize it was in the process of being elevated while they were staying there.

This process was largely completed in the 1960s, and much of the city, as it existed at the time, was raised by 4 and 14 feet—and that provided space for the new sewage system that would help with all those water and water-borne illness issues, while also establishing a new baseline altitude for future developments, which would be able to use that same sewer system while also being lifted up high enough that flooding and similar water-adjacent, low-lying land issues wouldn't be a problem most of the time.

What I'd like to talk about today is the issue of subsidence in other cities around the world, today, and some of the solutions we're seeing deployed to address it.

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The world is packed with sinking cities: a term typically applied to urban centers that are rapidly losing elevation, sinking into the ground due to a combination of natural and human instigated variables.

Chicago is a sinking city, as though all that lifting back in the 19th century helped it with both immediate and potential future, sinking-related problems, the Chicago metro area is still primarily built atop clay which contracts as it's heated.

This heat-related deformation hasn't always been much of an issue, but as more buildings have been erected and as the shift in our global climate has led to on-average higher temperatures for more of the year, the ground beneath Chicago, and quite a few other cities worldwide, has been slowly but measurably deforming, expanding and contracting more rapidly and dramatically due to temperature swings, which in turn has caused building foundations to shift and the surface, the ground upon which residents walk and build and live, to sink downward, which causes damage to those building foundations and to infrastructure that doesn't flex to accomodate this movement past a certain point, like roads, bridges, power lines, and basically everything else that makes up a city.

The majority of sinking cities, those at the top of the list in terms of ground deformation and elevation loss, anyway, are located on coasts, and because about 2.15 billion people live in near-coastal zones, and around 898 million live within the most directly impacted, low-elevation coastal zones around the world—both of those numbers steadily rising as more people move closer to the world's on-average wealthier and more opportunity-rich coastal areas—this is a significant and growing issue because the costs and dangers associated with such areas are also increasing, in part because larger populations tend to amplify the same.

A study published in 2022 that looked at the subsidence rate in 99 coastal cities from 2015 to 2020, intending to get a more accurate sense of just how rapidly they're sinking, found that while sinkage is occurring most rapidly across Asia, it's also happening on all the other inhabited continents—all of them except non-city-having Antarctica—and while the latent properties of these areas are partly to blame, human activity, especially the extraction of groundwater, is often a primary culprit causing these cities to sink.

Even more alarming, in some ways, is that while experts are already alarmed about rising sea levels, as ice caps and glaciers and other stores of water melt due to higher average temperatures and more frequent and dramatic heat waves, the rate of subsidence in most of these sinking cities is higher than the rate of sea level rise.

In other words, sea level rise is already causing insurance companies to leave some coastal areas and government coffers to run dry as they attempt to shore-up regions that are being lost to global oceans, but it would seem that many cities that are subsiding in this way are sinking faster than the water around them is rising—so the two opposite movements in parallel are amplifying those sea-level-rise-associated issues, but the issue of subsidence, which hasn't been as big a focus in mainstream conversation thus far, would seem to be the larger issue in many cases, and not terribly well addressed in most cities where it's an issue.

Important to note is that just as subsidence isn't a single cause problem, since it's the consequence of both natural features and human activity, it's also not a single consequence issue: just as Chicago suffered from both flooding-related and disease-related problems tied to subsidence, so too do these other sinking cities suffer a portfolio of associated ailments.

Probably the most immediate concern for most sinking cities, today, is similar to that of sea level rise.

While it may be common to imagine that rising sea levels will someday leave threatened cities underwater 100% of the time like a modern Atlantis, the real issue, today, is that as the ocean gets higher, closer to the level of coastal land, it takes smaller and smaller perturbations in that water for it to surge inland, covering more and more territory.

So buildings and roads that previously flooded once every ten years will flood every year, those that were previously inconvenienced by minor floods will be severely, perhaps permanently damaged by deeper and more intense floods that stick around longer, and areas further inland that were previously protected from surging ocean waters will start to flood, despite never having experienced flooding previously, and thus not being built to standards that would allow them to survive even relatively minor flooding.

Again, the combination of sea level rise and subsidence is basically doubling the impact of this sort of issue, causing more intense and regular flooding in these regions earlier than was previously anticipated, and thus messing with or totally screwing over plans made by city governance to handle such problems.

I mentioned earlier that the consumption of groundwater is often a component of this problem, and the general idea is that when modern humans move into a new region, they typically drill wells and start pumping water from deep underground, moving that underground water above ground for all sorts of uses, from drinking to filling our toilets to watering our lawns to manufacturing-related applications.

Moving all that water from underground to aboveground is similar, in terms of consequences, to moving a bunch of rock or soil from underground to aboveground: it causes the remaining ground to sink, because there's less stuff down there to hold everything on the surface up at its existing level.

Some previously sinking cities, like Tokyo, have been able to largely halt their subsidence by reducing the pumping of groundwater, Tokyo officials having implemented regulations to address the issue in the early 1960s, which brought their sinking issues to an end about a decade later.

Shanghai did something similar, but instead of halting all groundwater pumping, they required that these underground supplies of water be refilled after extraction, so the amount of water down there stays roughly equal, even if some is pumped for various uses sometimes—another way to accomplish essentially the same end, and a solution that seems to have not quite halted, but significantly slowed sinkage in Shanghai in the years since that policy was implemented.

Houston, in the US, also introduced groundwater remediation efforts in the 1970s, which seemed to have helped slow its sinkage, as did the Silicon Valley area in the 1960s.

The fastest-sinking cities in the world, today, according to that new study, and other recent research into the same, are Tianjin, Semarang, and Jakarta, the first of which is located in China, and the latter two of which are located in Indonesia.

These three cities are sinking almost 15-times faster than global mean sea levels are rising, and this is a big part of why the Indonesian government decided to move its capital from Jakarta to a new city the government is building on the island of Borneo.

It's estimated that one-third of Jakarta could be completely submerged essentially 100% of the time by 2050, and there are about 10.5 million people living in Jakarta, so that means a lot of people whose homes and businesses and neighborhoods are prone to flood regularly, today, may be gone completely, lost to the ocean, by mid-century—which by any measure is a highly destabilizing sequence of events, and will almost certainly lead to a large number of lost lives and a huge sum of lost wealth, not to mention the secondary issues that may arise as all those people moving out of these no longer habitable areas move elsewhere, stressing the systems in those new areas, including but not limited to the need for more water, which may need to be pumped from underground, causing more urban centers to sink, or to sink faster.

Jakarta is not alone in facing this heightened risk: there are many other big population centers around the world that are prone to similar outcomes, including but not limited to Chittagong and Dhaka in Bangladesh, Manila in the Philippines, Karachi in Pakistan, Kolkata and Mumbai in India, Guangzhou in China, Ho Chi Minh City in Vietnam, Bangkok in Thailand, Miami and New York City and New Orleans in the US, and Mexico City in Mexico, alongside many, many other cities that are built on naturally subsidence-prone land, are draining that land's groundwater or oil or other underground resources, are building heavy infrastructure on the ground which causes it to settle and sink, and in some cases are built atop or near shifting tectonic plates that rumble continuously enough that the sediment is pretty much always naturally compacting, the ground always deforming just a little bit, and all that adds up over time, causing the same or similar issues.

The most immediate consequences we're seeing in many of these areas is that insurance companies are leaving because it's no longer a winning bet to be operating in increasingly disaster prone regions, and that is likely to spread to other industries that no longer want to invest in assets that may be underwater part time or all of the time before they're expected to recoup their investment cost.

People will either leave these areas, fleeing for more secure ground, or they'll stay, putting their lives and their wealth of various kinds at risk as they do so.

Poorer people, so far at least, have tended to bear a disproportionate amount of the burden associated with these sorts of shifts, and resultantly the human and economic costs associated with impoverished populations are tending to increase, as is the number of impoverished people in afflicted areas, because of that aforementioned risk to wealth, an accompanying lack of security, and the increasingly difficult time people and businesses are having insuring their assets in these areas.

There are efforts to mitigate subsidence underway in some of these regions, including the use of advanced tools like LIDAR and satellite imagery to pinpoint the primary regional causes of sinkage, and the passing of policies, like the groundwater regulations introduced in several sinking cities in the 20th century, that then help halt or slow their city's subsidence rate.

Many cities are reorienting around an adaptation strategy, too, in part because sea walls and similar solutions don't work as well when it's not just sea level rise you have to worry about, and in part because the costs are more moderate than completely revamping a city's infrastructure to account for all that sinking.

In most cases this means deploying a series of systemic changes alongside relatively light-touch infrastructural ones, so increasing the ground's capacity to sponge-up water, rerouting, replacing, or removing water-based infrastructure that can reduce a city's capacity to absorb rainfall, planting trees and similar water-breaks in flood-prone coastal areas, introducing early warning systems and evacuation plans in case of severe flooding, and overall attempting to allow flood waters to roll through with the minimum amount of damage, rather than struggling, and failing, to keep it out entirely.

We're in the early days of this sort of adaption and mitigation evolution, though, and a lot of what we're trying now likely won't work as well as we had hoped—not everywhere it's tried, at least—and other solutions will almost certainly emerge in the coming years that turn out to be much more effective, and possibly cost-effective, too.

The sheer expansiveness and significance of the problem, though, will necessarily spark the innovation of a variety of approaches, systems, and technologies, and it's possible we'll see a flurry of new moderating elements deployed and installed in the coming years—alongside a slew of fresh tragedies in cities that suffer essentially continuous problems related to subsidence and flooding, in the meantime.

Show Notes

https://arstechnica.com/science/2024/01/east-coast-ground-continues-to-collapse-at-a-worrying-rate/

https://news.northwestern.edu/stories/2023/07/the-ground-is-deforming-and-buildings-arent-ready/

https://www.cambridge.org/core/journals/cambridge-prisms-coastal-futures/article/population-development-as-a-driver-of-coastal-risk-current-trends-and-future-pathways/8261D3B34F6114EA0999FAA597D5F2E2

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL098477

https://piahs.copernicus.org/articles/372/189/2015/

https://www.pbs.org/newshour/world/why-indonesia-is-moving-its-capital-from-jakarta-to-borneo

https://en.wikipedia.org/wiki/Sinking_cities

https://archive.ph/YVJdq

https://faculty.washington.edu/jwh/207mexic.htm

https://qz.com/2155497/coastal-cities-are-sinking-faster-than-sea-level-rise

https://climate.nasa.gov/news/3285/nasa-led-study-pinpoints-areas-of-new-york-city-sinking-rising/

https://www.washingtonpost.com/climate-environment/2023/05/30/land-sinking-us-subsidence-sea-level/

https://en.wikipedia.org/wiki/Raising_of_Chicago

https://en.wikipedia.org/wiki/Chicago_1885_cholera_epidemic_myth

https://en.wikipedia.org/wiki/Subsidence

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