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Tehran is sinking, and with it, much of Iran. This is a plain fact, not a metaphor for the country’s political and environmental crises. Because of excessive groundwater withdrawal, worsened by a structural water shortage, the soil beneath large areas of the capital is sinking by up to 30 centimetres a year, threatening buildings and infrastructure.
The situation, just one of several environmental problems affecting the city, has become so serious that President Pezeshkian has revived an old and highly improbable idea: relocating the capital to the Gulf of Oman.
An accelerating crisis
Cracks in buildings and roads, windows and doors that no longer shut properly, and constant repair work on the rail network. These are familiar scenes for 3 out of the 12 million residents in the Tehran metropolitan area, and an almost daily reality for the 350,000 people living in the most severely affected zones.
Subsidence, the lowering of the ground caused by the compaction of part of the subsoil, primarily due to excessive extraction from aquifers, has been ongoing for around thirty years, but is now accelerating: 18 centimetres a year on average, with peaks of over 30. The phenomenon is particularly acute in Shahriar, a predominantly agricultural area northwest of the city, and in the southwest (including historic, densely populated neighbourhoods such as Yaft Abad). It also affects the international airport, 14 metro stations, and key railway lines.
"The damage varies with the characteristics of the buildings, and geological conditions", explains Mahdi Motagh to Renewable Matter, from the Helmholtz Centre for Geosciences in Potsdam. "The damage is not necessarily high where the subsidence is greatest; the gradient caused by differential settlements between infrastructures and surrounding areas plays a significant role."
The environmental causes of subsidence and the dream of moving the capital
In general, subsidence can be triggered by various factors: the natural compaction of sediments, the weight of buildings, or the extraction of hydrocarbons. But in Tehran, the over-extraction of groundwater is practically the only factor to blame. Today, the capital’s aquifers are severely overdrawn by agriculture, industry, and domestic wells, while their natural replenishment is hindered by excessive concrete coverage. Although agriculture contributes little to the city’s GDP, it remains by far the biggest culprit.
Subsidence and water scarcity are not the only environmental issues surrounding the capital. Tehran sits in a highly seismic zone. Its location, over 1,000 metres above sea level in a semi-arid region, combined with uncontrolled urban sprawl and heavy traffic, makes it one of the most polluted capitals in the world.
This combination of risks led the government last March to dust off a project that had been dreamt of since the Islamic Revolution of 1979: relocating the capital to the Makran region, on the coast, in what is seen as a strategic position. After Indonesia, Iran would become the second country to move its main city (also) due to subsidence.
Between enormous costs and the fact that even on the coast fresh water is scarce, the idea seems unrealistic for now. However, the picture of an uninhabitable Tehran painted by the authorities themselves highlights the urgent need for more concrete plans to find a solution.
Subsidence, a national problem
Subsidence in Iran is far from limited to Tehran. The country ranks among the five worst affected globally, both in terms of the scale and speed of land sinking. According to a recent study (which includes an interactive map) that counts Motagh among its authors, it affects 3.5% of the national territory: some 56,000 square kilometres, of which 3,000 at rates exceeding 10 centimetres per year.
These may seem like small areas compared to the country's overall landmass, but they correspond to the most densely populated and economically productive inland plains, home to 14 million people (around one-fifth of the population) and the heart of Iran’s agricultural and industrial output. Fifteen percent of the national rail network and 8 of the country’s 61 medium-sized airports are considered at risk. Even sites of immense historical value, such as Persepolis, are threatened by ground collapse.
“All of Iran is affected because all developed areas are sinking. Only one province, Gilan, is spared," explains Motagh, who adds: "The causes of subsidence and water scarcity in Iran are all man-made, but climate change will make them worse. The level reached is such that today, I would say, it’s impossible to truly address."
As in Tehran, the phenomenon is largely driven by agriculture, particularly in regions dominated by water-intensive yet highly profitable crops. In Rafsanjan, famous for its pistachios, the land is sinking by more than 37 centimetres a year.
A thermometer for the water crisis
Subsidence is also a stark indicator of the ongoing depletion of Iran’s aquifers. Each year, according to the study by Motagh, more than 1.7 million cubic metres of water are missing from aquifers. The arid climate, political isolation, and the rhetoric of agricultural self-sufficiency exacerbate the situation.
The government is primarily focusing on large-scale projects such as desalination (with 65 plants already in operation and 95 under construction or planned) and huge water diversion projects to developed regions in difficulty.
"Technological solutions help, but what is needed above all is a shift from resource-extraction-driven development to a sustainability-centered model. And this means implementing new policies and economic models for agricultural development in Iran that look not at the next 5 or 10 years, but at the next 50 or 100. And this is still lacking”, Motagh sighs.
Subsidence, a global problem
Subsidence is a global phenomenon: over 2 billion people live on land that sinks by more than half a centimetre per year, mainly concentrated in East Asia (in China, 45% of urban areas and a third of the population are affected). In coastal areas and river deltas, its effects are combined with rising sea levels, exponentially increasing flooding and inundation.
While Iran is paying the price for this phenomenon, at the other end of the geopolitical spectrum, the United States is discovering that 25 of the country's 28 largest urban areas are sinking. When the ground gives way beneath our feet, even historical enemies find themselves on the same side. Or at least they should.
Cover: Teheran, Milad Fakurian, Unsplash