For hundreds of years, the ancient Persian empire used sloping tunnels known as ‘qanāts’ to access groundwater and channel it into towns and villages across what is now Iran . Even the capital, Tehran, far from any major rivers, was supplied entirely by qanāts until the 1930s. However, the city has expanded rapidly over the past century, and now comprises a vast urban landscape encompassing over 12 million residents. Despite the construction of dams on the Karaj, Jājrūd, and Lār rivers in the Elburz mountain range, groundwater has continued to be a primary source of water, with the number of city wells escalating from fewer than 4000 in 1968, to more than 32,000 by 2012.
New radar satellite data reveals the dramatic impact this has had on the stability of the city’s foundations. Between 1984 and 2011, groundwater supplies beneath Tehran sunk by as much as 12 metres, causing an area covering more than 700 sq km (270 sq miles) to subside by several metres. These findings were discovered by combining two decades worth of satellite data which monitored changes in subsidence in both agricultural and urban areas, with data obtained by the newly developed European Space Agency (ESA) Copernicus program, which updates every twelve days. As well as irreversibly damaging the groundwater basins and raising the risk of the city running out of water, the subsidence has resulted in the opening of crevices in the ground and buildings cracking under the pressure of the earth collapsing beneath them.
‘Lots of illegal wells have been operating in Tehran and in the country over the last several decades,’ explains Dr Mahdi Motagh, professor of radar remote sensing at Leibniz University Hannover and the GFZ German Research Centre for Geosciences. ‘In recent years the government has tried a lot to close some of those illegal wells. But this is not enough. Other practices like flood spreading, recharging the aquifers through watershed management practices, adapting new types of agricultural products that need less water compared to those already planted, and relocating the industries that heavily depend on water to other areas are among those practices that can be adapted to address the water problem in Tehran.’
Get the best of Geographical delivered straight to your inbox by signing up to our weekly newsletter and get a free collection of eBooks!