Four Letter Word: Subsidence

Four Letter Word: Subsidence

Subsidence must be a four-letter word because it’s rarely used in media stories about flooding.

Miami is the poster child for flooding, supposedly caused by climate change.

Bloomberg Businessweek published a lengthy story in its September 3 issue about flooding in Miami, where it mentioned climate change 15 times, but never mentioned subsidence.

The USGS reports: 

“More than 80 percent of the identified subsidence in the Nation is a consequence of our exploitation of underground water.”

“In the United States, more than 17,000 square miles in 45 States, an area roughly the size of New Hampshire and Vermont combined, have been directly affected by subsidence.”

Subsidence from using water from aquifers is the major cause of flooding in Miami, and in other states, such as North Carolina.

Sea level rise will contribute to flooding in Miami over the next 100 years, but at a very slow pace.

Sea levels will continue to rise, as they have for the last several thousand years, at a rate of 8-10 inches per hundred years. The IPCC, a group favored by AGW enthusiasts, showed that, from 1901 to 2010, i.e., 109 years, sea levels rose at the rate of slightly over 8 inches per hundred years.

The following data is from the paper, Contribution of land subsidence to the increasing coastal flooding hazard in Miami Beach.

“Portiona of Miami have subsided at the rate of 12 inches per hundred years, but since subsidence from the aquifer covered less time, it’s been estimated that subsidence has amounted to around 7 inches over the past 80 years.”

“Miami Beach satellite data showed subsidence at the rate of 7 inches per hundred years from 1993 to 2005.”

While the USGS has considerable data on the Everglades, it hasn’t published subsidence data on Miami.

A detailed paper by Kip Hansen, Wattsupwiththat, showed that Miami is also suffering from having built portions of Miami below mean higher high water (MHHW). 

“MHHW is the level of the water at the higher of the two daily high tides” or what could be called the High Tide Mark. Some of the pictures routinely published by the media are from areas built below the high tide mark, i.e., MHHW. 

Meanwhile, the USGS has published data on the Chesapeake Bay and on the Galveston areas.

Quoting from USGS: 

“A new interactive web application illustrates how groundwater, sediment compaction, and land-elevation change are related in the Houston-Galveston region in Texas.”

Subsidence for Galveston Area, from USGS website

Some of the subsidence along the East Coast of the United States is from isostatic rebound, where the Earth has risen or subsided due to the lifting of the weight of glacial ice from North America.

The National Geographic magazine published an article on flooding in New York City that ignored several inches of isostatic rebound when its cover showed a picture of the Statue of Liberty with sea water up to its waist.

Quoting Forbes Magazine, 

“This [isostatic rebound] has resulted in the East coast of America to slowly but steadily sink relative to the Atlantic Ocean.”

Subsidence is a major contributor to the apparent rise of sea levels along the East coast, and has been ignored by the media when it has published articles about coastal flooding … including flooding in Miami, Florida.

Sea levels will continue to rise at around 10 inches per century, while subsidence will continue as long as we draw water from the aquifers and the Earth continues to rebound from the last Ice Age.

Flooding in Miami, North Carolina, Galveston or New York City has nothing to do with global warming and CO2.

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8 Replies to “Four Letter Word: Subsidence”

    • While it actually takes place around the world, it is primarily noticeable along the East and Gulf coasts of the US because of subsidence.

  1. Thank you for the article. I am more than a little confused, however. Subsidence is the “sinking” of earth due to the reduction of groundwater, which had helped to support the earth above the aquifer. However, I thought “isostatic rebound” was the rise of earth due to the elimination of the ice sheet which previously weighted on the earth and “pushed” it down..

    If that is correct, then the two terms are in opposition. It seems they are used to compliment each other in the Forbes article quote used above?

    • Thanks for the question. Isostatic rebound has two effects. At the center of where the ice had been located, the earth would have been pushed down, while at the edges it would have risen. Now, with the removal of the ice, the earth at the center of where the ice was located would be rising, while at the edges it would be subsiding.
      In Stockholm Sweden, for example, it would seem as though sea levels were getting lower, while in New York City they would seem to be rising.

    • Think of the continental crust as like a semi-rigid plate. Push down on one side and the other side goes up. Then when that glacial weight is removed, the opposite occurs.

  2. The land is sinking all around Chesapeake Bay. The relative sea rise at several tidal stations ranges over ~3 to 6 mm/yr, but the land subsidence ranges over ~1-4 mm/yr. Land subsidence is about half (38-69%) of the measured tidal sea rise rate. Thus, the real rate of sea rise around Chesapeake Bay is only around 2 mm/yr.
    The sea rise rate since 1905 at Galveston TX has an average value of 6.47 mm/yr. But the land there is sinking at ~4.76 mm/yr, so the real sea rise rate is only 1.71 mm/yr.