Sinking Cities and Rising Sea Levels – Rise for it?

Guest essay by Kip Hansen – April 21, 2022

The field of sea level rise, as a scientific enterprise, is rife with all sorts of factors that make published, as published, scientific results unreliable. The most unfortunate thing is that these unreliable results are then considered as proven fact and translated into talking points by activists and seen by policymakers as Sciencealthough tentative statements and warnings are included in the original research report.

The media are always complicit. Active journalists, with a predetermined story given to them by their Editors, catch up with each little research and sift it to find points that match the story they have been told to write. .

Sidebar: You might think this is conspiracy thinking. Let me quote an email newsletter I received earlier this week from Including climate right nowissued marching orders for journalists from the week of April 11 to April 22, 2022:

This is the latest product from Katherine Kornei written in Scientific news:

“Coastal cities around the globe are sinking – Subsidence makes coastlines even more vulnerable to sea level rise.

“Coastal cities around the globe are sinking an average of a few centimeters per year, satellite observations reveal. The one-of-a-kind punch of subsidence and rising seas This means these coastal areas are at greater risk of flooding than previously thought, researchers report on April 16. Geophysical research letter. ”

“By measuring the duration and intensity of those reflected waves, the team was able to determine the height of the ground with millimeter accuracy. And because each satellite passes over the same part of the planet every 12 days, the researchers were able to track how the ground deforms over time.”

“The greatest rates of subsidence – up to 5 cm per year – are mainly in Asian cities such as Tianjin, China; Karachi, Pakistan; and Manila, Philippines, the team found. Furthermore, a third or 33 of the cities analyzed are sinking in some places by more than a centimeter per year. ”

This is valuable information for cities to know if they are over-exploiting water (or gasoline, oil, etc.) from beneath their city causing serious subsidence problems. Cities that are 30 feet (10 meters) above sea level in their locality don’t have to worry about flooding due to subsidence – they need to worry about Valley were already too close to local sea level and were likely to be inundated by exceptional high tides and storm surges from the storms they experience today. Cities need to worry about their locality Relative sea level change – represent combine their local absolute sea level changes and local land subsidence. As you will see above, many areas of the coastal cities studied are located not on the coast, but inland away from the sea.

Some places have caused The situation itself is quite dire due to the pumping of water from below the cities. Jakarta is one, I wrote about it here. I point out that of the six cities in the image below (from another study), “Jakarta led the group that sank over 3.5 meters (almost 12 feet) in the ten years from 1990 to 2000.” Of course, that’s just a specific part of Jakarta that’s subsided so much. The subsidence – subsidence – of Asian cities is nothing new. It is not news.

In a new study by Wei et althey found that cMajor cities around the globe are sinking an average of a few centimeters per year. It would be great if there were science journalists who didn’t fall into the knowledge black hole where unrelated things can be averaged to a single meaningful number. The statement is not even true for the example cities in the original study. Here is an example of what is being discussed in the article:

Here we see Tampa, Florida, in two versions. The one on the left is the average velocity of Vertical earthquake motion (VLM) according to the authors and to the right a satellite version of Google Map. I’ve moved the white squares representing the satellite groundwater wells to the VLM graphic as black squares and added a red square where the tide gauges for Tampa Bay are located. The red line that cuts across the northwest portion of the bay is a causeway and is shown to be sinking about 5mm/year, equivalent to the thickness of 3 stacked US$1 coins or 2 €50 cents. . We see that for Tampa/St. Petersberg (St Pete), the northern part of the Gulf is shrinking in the range of 4-6mm/year, but other areas east of the bay are increasing and the southern tip of the St Pete peninsula is also increasing . Looking at the area with Google Earth, we see that the subsidence areas have formed small lakes of holes, many of which will be formed by sinkhole. Absorbing water from the porous rock beneath this area causes the surface to sink. The area to the north and west of the causeway is Dunedin, which sits atop about 80 feet above sea level.

SONEL gives VLM for St Pete/Tampa Bay tidal station (red box) at -0.5 to -1.8 mm/year (depending on GPS solution used), generally agree with figure research photo.

And “average” for Tampa/St Pete? Who knows. There’s nothing to mean by averaging. For a city like this, it seems likely that subsidence could be caused by pumping groundwater reserves or possibly due to the general porous nature of Florida’s subsurface rock.

So as the data from the study sounds, there are areas of Tampa/St Pete that are sinking at a rate of ~5mm/year. However, this Not and cannot one “one or two punches to subsidence and rising seas“.

The sea level of concern for Tampa/St Pete is a measure of Relative Sea Level using a tide gauge there. It shows that the combination of sea level rise and subsidence at the tide gauge is about 3 mm/year – that is combine character. That actual measurement is about what would be expected from the generally accepted absolute sea level of 1.7/1.8 mm/year and settlement of 1 to 2 mm/year at tide gauge. In a century that would result in a relative sea level rise of less than 1 foot.

One of the study’s authors, Matt Wei, is quoted as saying: “We tried to strike a balance between population and geographic location,” he said. While the subsidence has been measured in previous cities, previous research tended to focus on only one city or region. This investigation is different, Wei said. “This is one of the first to really use data with global coverage.”

Of course, the author admits: “We measured subsidence rates in 99 coastal cities around the world between 2015 and 2020 using satellite data. The subsidence rate is very different in cities and from city to city. “That’s right, because subsidence is purely a local problem – local to the city’s subdivisions. Interestingly, they determined flood risk based on: “To estimate the subsidence areas most likely to increase the risk of future flooding, we estimated the total area in each metropolitan area. The urban area has an elevation of less than 10 m above sea level and subsides faster than the LOS 2 mm/year (Figure 1b). The 2mm/year threshold is comparable to the global average sea level rise rate. We have chosen a 10 m elevation threshold because the flood is up to 9.1 m during Hurricane Katrina in 2005 (Fritz et al., 2007) and high tides will continue to increase as sea level rises (Garner et al., 2017). ”

The subsidence data in the study were obtained from the Sentinel series of satellites. The latest Sentinel-6 – the most accurate – has a measurement uncertainty that, according to its official specifications, has “The combined standard measurement uncertainty is 3.46 cm [ 1.36 in ] for LR ALT-NRT and products 3.35 cm [ 1.32 in ] for HR products ALT-NRT. ”

[NRT = Near Real Time,   ALT = Altimetry,  LR =  Low Resolution,  HR = High resolution   Combined standard uncertainty should be notated as  +/- ]

“Wei and his team relied on observations made between 2015 and 2020 by a pair of European satellites. Onboard devices emit microwave signals towards the Earth and then record the reflected waves back. By measuring the duration and intensity of those reflected waves, the team determine the height of the ground with millimeter accuracy. ” [ source ]

The study authors, like many groups of sea level satellites, argue that the Sentinel series satellites can determine altitude (of ground or sea level) with millimeter accuracy. That is likely not true according to the satellite system specifications, cited above. However, combined with ground mounted GNSS stationthey can tend to VLM in millimeters within 5 years.

Overall, research full here, which is annoying to read and watch. All illustrations use magenta for the alarm effect, and the color index varies from image to image, so they cannot be easily compared – for example, in some colors magenta the VLM is -10 mm year, in another it is -2 mm/yr.

Bottom line:

1. Some coastal cities were found to have areas that are sinking. The same is true for non-coastal cities. This has been known from other studies. Rapidly growing megacities in less developed countries suffer from more severe subsidence problems due to the extraction of groundwater from just below these rapidly growing megacities. Although this has been known before, it is important that local authorities and planning agencies know and understand.

2. No groundwater extraction subsidence problems are strongly related to sea level rise, if any.

3. Almost every riparian property in the world that is not on a foundation, especially ports with docks and piers, is sinking to some degree because they are often built at the confluence of rivers and seas lying on artificial land filled with the original shoreline. This subsidence combined with absolute sea level rise (sea level rise) increases the risk of flooding.

4. Even just idea of the averaged subsidence from disjointed, geographically widely separated cities worries me about how science is being done today.

# # # # #

Author’s comment:

In fact, the article under discussion causes me to be treated as an article written for the sole purpose of being “published”. It’s filled with keywords to attract attention from magazines: Global, (alert about) sea level, human activity… can be the main cause, etc. all lead to one child. alarming number.

The authors exacerbated my sense of rightness by the foolish unscientific act of averaging various unrelated data – used to create a prime example of One number to rule them all wrong (the tendency to try to reduce complex problems to a single number).

Longtime readers will know that I have written many times about cities being threatened by sea level rise (and many are) and that most of the sea threats are actually caused by subsidence. land.

Thanks for reading.

# # # # #