What a paradox! Mexico City is always either too wet or too dry

There may be other major global metropolises (Los Angeles springs to mind) that have invested more effort and money than Mexico City to bring in water from afar. But there is surely none that has invested as much effort and money to send the water back out.
Mexico City’s hydrological paradox is that (unlike Los Angeles) it gets more than enough rain to, in theory, keep the 21 million people who live in and around it adequately supplied with water. Its average annual precipitation is about twice that of Los Angeles, and even exceeds that of famously damp London. But most of the rainfall comes during the summer, and often during just a few epic storms. So when it’s wet, it’s way too wet, and the city has built a massive infrastructure over the past five centuries to get the water out quickly. To keep hydrated during the drier months, Mexico City imports water from other regions but mainly just pumps from underground, which causes land subsidence, which makes flooding worse.
A number of major world cities have run into big water problems lately. Cape Town has begun planning for “Day Zero,” when the municipal water supply runs out. Sao Paulo was hit with frequent water shutoffs during a drought in 2014 and 2015.
Climate change is often cited as contributing to these water shortages around the world, and maybe it has. But up to now, its effects appear to have been minor compared with more local causes, such as deforestation, pollution, population growth, sprawl and poor planning.
Mexico City is a perfect illustration of this: Warming global temperatures are likely to bring more rainfall to the mountains south of the city that are key to its water supply. But if current development patterns continue, the water will be squandered. Barring a significant change in approach, “the city will have a huge problem with water availability in very few years,” Zambrano told me.
Nature did once provide a straightforward way to store the area’s rainwater, with a network of big, shallow lakes in the heart of the Valley of Mexico that filled up during the wet months and receded when it was dry.
According to legend, the Mexica, aka the Aztecs, built their capital on the island in 1325. They built long causeways to link their island to other parts of the valley, allowing them to control a large, prosperous region from one central base. The causeways also did their part to preserve water quality, sequestering the saltiest, most polluted water in Lake Texcoco to the east of the city.
Even the Mexica struggled with frequent flooding, though, and their Spanish conquerors soon began trying to engineer their way out of the problem, building a channel in the 1600s that drained the northernmost of the lakes in the Valley of Mexico into a neighbouring valley. That was supplanted by a succession of bigger, better but never quite sufficient drainage canals and then tunnels, the latest being the Túnel Emisor Oriente, which has already cost more than $2 billion and still isn’t quite done.
This great draining also left the city with a lot less water, the lack of which began to pose problems around the turn of the 20th century. A succession of projects to bring water in from elsewhere, culminating with the 200-mile-long Cutzamala system completed in the 1990s, partially addressed that. But pumps played an even bigger role, with groundwater extraction now providing about 70 percent of the area’s water. That has made the ground sink. It also may be increasing the city’s vulnerability to earthquakes. And it has been delivering water of increasingly poor quality; in some poorer parts of the city, it isn’t reliably delivering water at all. In a city with ample precipitation, this seems not only perverse, but also like it ought to be easily fixable.
Here’s another press-conference comment from Slim: “We need to take advantage of all the rain water. It’s a problem that can be solved with a relatively low investment.” Manuel Perló Cohen, an urban planning scholar at UNAM’s Institute for Social Research and a leading voice on Mexico City water issues isn’t so sure about that: “We have plenty of rainfall, but it’s not easy to translate that into systems.” That is, the city has built a vast, complex system to bring water in and ship it out. There is at this point almost no infrastructure for water reuse or rain capture within the city.
Perló and architect Loreta Castro Reguera Mancera are the driving forces behind a still-under-construction park in a former flood basin on the east side of the city that enables groundwater recharge and recently won a top global sustainable-design award. There are a couple of recently built linear parks in the middle of roadways that incorporate water reuse or treatment into their design. In 2016, the city government, with help from Dutch water experts and others, compiled a hopeful report cataloging the ways in which different neighborhoods could contribute to building a more rational and resilient water system.
Meanwhile, what Perló calls the ‘pathological-stable hydraulic system’ of Mexico City lumbers on. “I believe that the current system should be changed,” he says. “It doesn’t have any sustainability, and it’s going down. Slowly, but it’s going down.” The question is whether a motley crew of billionaires, reformers and city officials will be able to cobble together a replacement before it does.
—Bloomberg

Justin Fox is a Bloomberg View columnist. He was the editorial director of Harvard Business Review and wrote for Time, Fortune and American Banker. He is the author of “The Myth of the Rational Market”