Iran at a Low Point: TehranIs Sinking, and It May Be Irreversible
A recentstudy based on analyzed satellite data shows that the Iranian capital issinking at a rate of 10 inches per year
Asaf Ronel
05.12.2018 | 01:17
Tehran issinking. This is not a metaphor connected to American sanctions or the drop inoil prices, but the conclusions of a recent study that analyzed satellite dataabout the Iranian capital. It found that some parts of the city are sinkinginto the ground at a rate of up to 25 centimeters (nearly 10 inches) a year.The researchers also found that the sinking areas are expanding and could reachthe city’s international airport.
Theresearch by two scientists from the GFZ German Research Center for Geosciencesat Potsdam was accepted for publication by the scientific journal RemoteSensing of Environment. The findings were also published on the website of thejournal Nature. The researchers used satellite tracking data from 2003 to 2017to track the rate of land subsidence in Tehran. A previous study linked the sinkage to the depletion of the groundwater aquifers under the city, which are being pumped to irrigate the fields surrounding the capital and to supply water to the city’s 13 million residents.
The newstudy describes the extent of the trouble. The western Tehran Plain, whichincludes the western city’s urban areas, farmland and suburbs, is sinking at arate of 25 centimeters per year. The Varamin Plain, an agricultural areasoutheast of the city, is sinking at a similar pace. The international airport,southwest of Tehran, is also sinking, albeit at a slower rate of 5 centimetersa year. Overall, the researchers estimate, about 10 percent of Tehran’s urbanarea is affected by the sinking.
Thesubsidence rate in Tehran is among the highest documented in an urban area,although this is a widespread global problem. Earlier studies have shown thatJakarta, the capital of Indonesia, is sinking at a rate of 20 centimeters ayear, while California’s San Joaquin Valley, whose cities include Stockton andFresno are located, is sinking by as much as 60 centimeters a year.
Alongwith the land subsidence, huge fissures, some of them several kilometers longand up to four meters wide and deep, have appeared in the ground southeast ofTehran. Some of these crevices threaten to bring down power lines and to damagerailways. Sometimes the cracks appear underground, creating sinkholes that area safety hazard. They also make farming unviable as irrigation water drainsthrough the cracks, leaving the soil dry.
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In aneffort to slow the subsidence, the authorities are trying to restrictgroundwater pumping. It is estimated that some 100,000 illegal wells acrossIran have been sealed in recent years, but in metropolitan Tehran alone thereare 30,000 such wells operating.
Theresearchers say the subsidence may be irreversible. Groundwater measurementsshow that the land does not rise back up when the groundwater increases, aftera heavy rain, for example. The findings show that the rock under the soil alsoloses some of its porosity when the ground sinks. This change could lead toanother worrisome phenomenon – more intense flooding because rainwater is notseeping into the ground.
