Seen by satellite and on foot around the city, officials warn that what they call land subsidence poses a grave danger to a country where protests over water scarcity already have seen violence.
“Land subsidence is a destructive phenomenon,” said Siavash Arabi, a measurement expert at Iran’s cartography department.
Over-reliance on ground aquifers has seen increasingly salty water pumped from below ground.
When you pump water from under the ground surface, you cause some empty space to be formed in the soil,” Arabi told The Associated Press.
Iranian authorities say they have measured up to 22 centimeters (8.6 inches) of annual subsidence near the capital, while the normal range would be only as high as 3 centimeters (1.1 inches) per year.
Either way, the numbers are alarming to experts.
German scientists estimate that land under the airport is sinking by 5 centimeters (1.9 inches) a year.
Some 2 million people live in the area, he said.
Already, the drought and water crisis has fed into the sporadic unrest Iran has faced over the last year.
Iranian authorities have begun to crack down on illegal water wells.