Depletion of Iran’s underwater aquifers is driving the ground to rapidly sink across the country, new research shows.
Over 12,120 square miles (31,400 square kilometers) of the country (almost the size of Maryland) travels downward faster than 0.39 inches (10 millimeters) per year. In a more extreme case, ground levels have decreased over an annual (34 cm) near Rafsanjan city in central Iran.
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Measurement of settlement
In Iran, approximately 60% of water supply comes from underground aquifers. To study how this affects the surface, Jessica Payne, a doctoral candidate in the Department of Earth and Environment at the University of Leeds in the UK, and her colleagues used radar data from the European Space Agency’s Sentinel-1 satellite constellations to map how Iran’s ground levels have changed over eight years between 2014 and 2022.
The researchers have discovered 106 regions covering a total of 12,120 square miles, or about 2% of the country.
“Iran’s sinking rates are some of the fastest in the world,” Payne told Live Science. “We found about 100 sites across Iran that sinks faster than about 10 mm. [0.4 inches) a year. In Europe, case studies are considered extreme if they exceed 5 to 8 millimeters [0.2 to 0.3 inches] year. ”
The ground is sinking due to groundwater extraction, she said. She said that 77% of the incidence of agriculture and the incidence of settlement faster than 10 mm per year correlates with the presence of agriculture.
For example, near Raf Sandjan city the climate is really dry, with pistachio farms and groundwater supply being used frequently. Paine may not appear to be a major reduction in 13 inches (34 cm) of sinking (34 cm) per year, but “10 years later, the ground is about 3-4 meters down. [10 to 13 feet];It’s really serious. ”
In the Bardaskan in northern Iran, the area found to be affected by subsidence was 429 square miles (1,110 square km). It is 40% larger than recorded in a 2008 survey. The work of Payne and her colleagues was published in the journal Solid Earth on August 27th.
“irreversible” sinking
Much of the sinking at all 106 locations was irreversible, Payne said.
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“The most striking conclusion of the paper is that the majority of groundwater-related subsidence in Iran is irreversible, highlighting the severity of aquifer depletion,” Shirzai said.
Aquifers do not function like reservoirs, she noted. Extracting more water than entering from the reservoir will lower the level. However, if it rains it can fill up again.
Approximately the same amount of water is removed and replaced with precipitation each year, aquifers have a seasonal decline trend called elastic recovery, Payne said. But when far more water is extracted, things change.
“Inside the aquifer it’s like a bucket of sand. There are layers of mud and sand, and the mud and grains of sand are separated by water,” Payne explained. “But if that water has been removed and not removed before, the sand and mud are not strong enough to lift not only the building above, but all the deposits above.”
As a result, the particles are flattened and ground levels result in an irreversible reduction in settlement. If water goes back into the system and penetrates the compressed parts, she said it won’t return the ground level to where it was.
The meaning of this is serious. “Slow slopes create cracks and structural instability, damaging buildings, roads and railroads,” Shirzai said. “Cities like Tehran, Karaj, Mashhad, Isfahan and Shiraz are directly affected. Karaj alone has over 23,000 people living in the Hazard Zone.”
“It’s hard to hear about the impact from outside of Iran, but anecdotely I’ve heard from an Iranian colleague that they have to abandon the building,” Payne said.
The subsidence is not inherent to Iran.
“Unfortunately, the scenario provided to Iran reflects the echoes that characterize many other countries and their metropolitan cities,” Francesca Cigna, a researcher at the Institute of Atmospheric Science and Climate in Rome, Italy, who was not involved in the study, told Live Science.
Other places where you can see a big drop are major cities in central Mexico, the US, China and Italy, she said.
“Iran’s peak rate is a rival to California’s Mexico City and Central Valley, and is placed in one of the world’s most extreme sinking hotspots,” Shirzai said.
Disasters related to subsidence are not unheard of. In Mexico, for example, land subsidence is believed to have contributed to the collapse of the subway world in 2021, resulting in 26 deaths and dozens of injuries.
Another major risk is loss of freshwater supply. “Continuous aquifer compression means that much of the storage capacity is permanently lost,” Shirzai said. “This will exacerbate water shortages during droughts, reduce resilience to climate change and make recovery more and more impossible.”
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