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December 06, 2022

It’s The Subsidence

Parts of Pakistan are sinking ten times faster than seas are rising.

Recently-flooded Pakistan is the poster child for “reparations” to be paid to third world countries by the developed world for the damages caused by climate change. However, the scale of the disaster is largely due to poor governance in Pakistan and local practices that won’t be cured by shoveling cash to the same kleptocrats who have swallowed up past foreign aid without improving the lives of their citizens. Almost all press accounts of the disaster fail to mention that so much water has been pumped out from under the areas which flooded that the land is sinking, a process called subsidence, much faster than seas are rising,

The monsoon rains were the worst in 40 years and may have been exacerbated by global warming (responsible scientists don’t attribute individual weather events to climate trends). There is more glacial runoff into the rivers of Pakistan than there used to be, certainly a function of higher temperatures. The seas are slowly rising. However, the disaster was preordained by the flood of people moving into the affected areas recently and deep drilling for water both to support expanded agriculture on the alluvial soil and water-hungry manufacturing in cities like Karachi, parts of which are sinking five times faster than the surrounding sea is rising. As the aquifers are depleted, the sandy soil compresses and the land above sinks. Earthquakes hasten the settling process as does the weight of new structures.

Until recently it has been almost impossible to distinguish rising ocean levels from subsiding land since the sea reaches further in both cases. However, satellite-based measurements now give us an extremely accurate measurement of both sea and land level. An article published by Voice of America in 2019 titled “Cities Sinking in Pakistan's Baluchistan Provincediscussed the sinking problem but without explicitly predicting the flooding:

“Local and American experts warn unchecked groundwater extraction in major urban centers in Pakistan's Baluchistan province has triggered the sinking of the land at a rate of 10 centimeters a year, causing cracks in buildings, roads, and agricultural fields.

“The land subsidence is occurring in numerous locations in northern parts of Baluchistan, including districts of Qilla Abdullah, Pishin, Mastung and the provincial capital of Quetta, the largest population center in the province [nb. an area very hard hit by flooding.]

“The area is arid and groundwater is the only source of water for domestic and agricultural use, said Professor Din Muhammad Kakar of the University of Baluchistan.

“’We have drawn a lot of water from the subsurface and the over-exploration of the groundwater has triggered the phenomenon of land subsidence since 2010,’ said Kakar, who is dean and chairman of the department of seismology.”

The alluvial plain is just above sea level and historically floods frequently; that’s why the soil is rich and doesn’t become depleted of nutrients. People build just above the most recent flood level (and sometimes below it). When the land sinks, the next flood of the same magnitude will reach more land than the one before it. When there is a forty-year flood through land which has sunk and become many times more populated since the last major flood, there is predictably a disaster. That’s what happened in Pakistan.

Subsidence is a major threat in many places beyond Pakistan.  A recent study measured subsidence worldwide:

“Satellite data indicate that land is subsiding faster than sea level is rising in many coastal cities throughout the world. If subsidence continues at recent rates, these cities will be challenged by flooding much sooner than projected by sea level rise models. We measured subsidence rates in 99 coastal cities around the world between 2015 and 2020 using satellite data. Subsidence rates are highly variable within cities and from city to city. The most rapid subsidence is occurring in South, Southeast, and East Asia. However, rapid subsidence is also happening in North America, Europe, Africa, and Australia. Human activity—primarily groundwater extraction—is likely the main cause of this subsidence. Expanded monitoring and policy interventions are required to reduce subsidence rates and minimize their consequences.”

An article in The Washington Post about the barriers built to mitigate flooding in Venice goes on and on about whether the wall will be effective as the sea rises. Buried at the end of the article is the main reason for recent flooding in Venice: the land the city is built on is sinking, largely because of water extraction.

It's politically popular to attribute all disasters to climate change. Ignoring other natural and man-made causes of catastrophe – like subsidence, makes it impossible to take effective avoidance and mitigation measures. No matter how many Teslas we drive or how many dollars we pay in reparations, Pakistan and many other countries will suffer increasingly severe floods so long as water is being pumped out from under collapsible sandy soil.

See also:

How Bad Governance Exacerbated Pakistan’s Flooding (from Foreign Policy)

How NOT to Convince Anyone about Global Warming (about subsidence in Norfolk, VA)

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