Mexico City could become the Aztec Waterworld if it keeps sinking every year

MEXICO CITY —  Seven hundred years ago, ancient Mexicans achieved an ancient engineering marvel: founding the city of Tenochtitlan on top of a lake surrounded by mountains.

They did not, however, anticipate that centuries later modern chilangos, as Mexico City residents are known, would have to deal with their complicated land choice. Mexico City, which now sits on top of Tenochtitlan, is sinking and it’s sinking fast

Today some of the capital’s churches are sinking into their foundation, seemingly swallowed up by sidewalks. Historic buildings are cracking, sagging, or tilting. Now, major restoration efforts are underway to help offset the damage.

“The subsidence problem in Mexico City is on record as being the most severe in the world,” Devin Galloway, chair of UNESCO’s Working Group on Land Subsidence and a hydrogeologist for the U.S. Geological Survey, told Fusion.

“Mexico is a point of reference for us, in part because of the severity of the problem, but also because of the cultural impact of the damage.”

He said the situation is also endangering many of Mexico City’s World Heritage sites.

What’s causing Mexico City’s ground to sink? The aquifers that supply the city’s groundwater are being depleted faster than they can be refilled, causing the ground to sink. Mexico City and the surrounding urban sprawl of more than 20 million people consume close to 287 billion gallons of water a year, 70 percent of which is drawn from its subterranean aquifers.

Before Mexico City became the world’s fourth largest city, before the vast subway system and bustling sidewalks, the Aztecs developed an intricate network of dikes and canals to manage interconnected fresh and saltwater rivers. But when the Spaniards arrived in 1521, the Aztec aqueducts and levees were destroyed during the siege of Tenochtitlan.

What had been a sustainable islet lake system gradually became solid — but iffy — ground, as the Conquistadors drained the lake. Five centuries later, the modern city still hasn’t become much smarter about its groundwater resources.

The European Space Agency recorded the subsidence over the course of two months in late 2014, noting that some areas are now sinking more than an inch a month.

The shifting land is wreaking havoc on the city’s plumbing and drainage systems, breaking pipes and leading to further collapse and cave-ins. It is estimated that more than 40 percent of the water pumped into the city is lost to leaks.

So how can Mexico City solve the problem and stay afloat? Well, there’s no easy answer.

“If you were really aggressive about replenishing [the subterranean aquifers] you could cause uplift, which itself could cause damage to these structures that have already equilibrated themselves to the current situation,” Galloway said.

So, parts of the city will likely remain crooked. And buildings will continue to lean.

The city is finally beginning to recognize the importance of water collection systems and other possible solutions, but apart from sealing off wells located directly under the historic center, Mexico City is still seemingly decades away from weaning itself off its groundwater dependency. And the city continues to drill wells to meet the needs of its residents, thousands of whom still lack access to running water.

If nothing changes and no significant engineering measures are implemented, well, you can just speculate that future chilangos might be eating tacos with the fishes.

Andrea Noel is a freelance journalist based in Mexico