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 (or hail, which hit parts of the city early Monday) 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 -- although recent rains should put that off for a while. Sao Paulo was hit with frequent water shutoffs during a drought in 2014 and 2015. All of California faced water-use restrictions during a drought that ended (for now) with the super-wet winter of 2016-2017.
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, 1 National Autonomous University of Mexico (generally known by its Spanish acronym, UNAM) biologists Luis Zambrano, Rodrigo Pacheco-Muñoz and Tania Fernández wrote in a 2017 article in the scientific journal Anthropocene. 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.
I became curious about Mexico City's water problems when, not long after my arrival there last week, the country's richest (and the world's seventh-richest) man, Carlos Slim Helú, launched into an extended discussion of them at a televised news conference. Until recently, agitating for a shift in the city's approach to water had been mainly the territory of academics such as Zambrano and an assortment of architects, engineers and activists. But Slim isn't the only business leader now getting worked up. The nonprofit Agua Capital was launched earlier this month with backing from some of the country's biggest corporations and a goal of finding "nature-based solutions" for Mexico City's water problems. Everybody seems more or less in agreement with Slim's basic diagnosis: "We need to stop over-exploiting the aquifer," he said. "We always have a lot of rain. We need to make it filter back down." 2 Still, that's a lot easier said than done.
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 -- a basin with no outlet to the sea -- that filled up during the wet months and receded when it was dry. Civilization began to develop around these lakes thousands of years ago. In the first few centuries AD, Teotihuacan, about 25 miles (40 kilometers) north of modern Mexico City, grew to be one of the largest cities on Earth, with a population estimated at more than 125,000. As I wandered last weekend around the monumental exhibits devoted to it and neighboring pre-Columbian settlements in the Mexican National Museum of Anthropology, I couldn't help but think that if modern Mexico City had been built at Teotihuacan or pretty much anywhere else in the general area, its water issues might be much less acute today.
But no, Hernán Cortés and his fellow conquistadors had to show up in 1519, when the region's dominant city was situated on an island in the lowest, most brackish of the valley's lakes. After conquering Tenochtitlan, the Spaniards stubbornly stuck with the same location, even after a flood left the city almost entirely submerged from 1629 to 1634. (Most of the historical exposition here is derived from a highly entertaining conversation I had with Manuel Perló Cohen, an urban planning scholar at UNAM's Institute for Social Research and a leading voice on Mexico City water issues. Any errors are of course mine.)
According to legend, the Mexica, aka the Aztecs,
built their capital on the island in 1325 after observing an eagle perched on a cactus, devouring a snake -- an omen that one of their gods had told them to keep an eye out for, and that is today depicted on the Mexican flag. Old maps give one the impression, though, that the militaristic Mexica also chose the location in the way that a spider chooses to perch in the middle of her web. 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 neighboring 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 enabled the city to spread out along the former lakebed, the only significant parts of which to remain undeveloped are the former Lake Xochimilco, now a landscape of farms and canals at the south end of the city, and the salt-encrusted final remnants of Lake Texcoco, which ran dry about a century ago as the city around it sank and is now in the process of being converted into a giant new airport (more on that in a future column). 4
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 (322 kilometer) 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, as already mentioned, 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. 5
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." Perló 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.
What there are, for the moment, are experiments. 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 (which themselves were built atop former waterways) that incorporate water reuse or treatment into their design. Agua Capital is backing a project, still in its early stages, to protect springs and promote sustainable land-use practices in the hills on the southern end of the city. In 2016, the city government, with help from Dutch water experts and others, compiled a hopeful report (warning, it's a huge file) 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.
The volcanic rock of the mountains is much more conducive to groundwater recharge than the clay soils (and sidewalks) of the central city.
Translation (and reporting) by Bloomberg News reporter Andrea Navarro, who was at the news conference.
Archaeologists and historians have settled on Mexica as the better name, since that's what the people called themselves. Although nobody seems to be agitating to change the name of Estadio Azteca.
I wrote a column last year about another former big, shallow lake in California that is now the richest agricultural area in the U.S., and also has big water problems. Yes, there seems to be a pattern here.
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