Mexico City has been featured a few times recently in the New York Times, with a focus on some of the fascinating hydrological history and its implications to modern urban life.  I was very ignorant of the specific characteristics of the city, and while I love Mexico have only had the chance to spend a long layover in Mexico City proper a few years back.  I learned much in these few articles, with a desire to dig deeper as well.

Climate Impacts

An article by Michael Kimmelman from February 17th, “Mexico City, Parched and Sinking, Faces a Water Crisis” is part of the ongoing ‘Changing Climate, Changing Cities’ series and includes a rich interactive experience, along with a compelling long form read (well worth it).

The history of Mexico City as a city has many facets, but two emerge in this context.  First is the concept that the city is built on a lake.  This map shows the configuration of the area around 500 years ago, about the time the Spanish arrived in Mexico.

Tenochtitlán, the major urban center, was established in 1325, a larger island surrounded by smaller areas islands amidst Lake Texcoco – shown as the City of Mexico below.  This aided in defense and provided agriculture using the chinampas, islands floated for growing crops.

The city was rapidly transformed via defeat and colonization:

Then the conquering Spaniards waged war against water, determined to subdue it. The Aztec system was foreign to them. They replaced the dikes and canals with streets and squares. They drained the lakes and cleared forestland, suffering flood after flood, including one that drowned the city for five straight years.

The article focuses on both this concept of geological transformation.  The second part of the story of Mexico City is the Grand Canal.  This infrastructural intervention was completed in the late 1800s, and ” a major feat of engineering and a symbol of civic pride: 29 miles long, with the ability to move tens of thousands of gallons of wastewater per second. It promised to solve the flooding and sewage problems that had plagued the city for centuries.”

The City being built on a lake has led to subsistence due to geological forces, and the need for drinking water has meant well drilling on a huge scale – both leading to elevations of the city being dramatically lowers.  This makes gravity-based infrastructure like the Grand Canal a bit problematic, as they can no longer freely drain.  The city, which occupied a metropolitan area of 30 square miles in 1950, now occupies closer to 3000 square miles, so and the almost 22 million inhabitants exert massive pressures on the land.

Some great interactive graphics from the NYT show the canal in the context of the ancient lake bed that sprawls through the region (see how this relates to the map above).

This plays out in the map below, which highlights the worst place of subsidence – the darkest red portions sinking around 9 inches per year.

[Click maps for larger views or check them out in the original article for overlay]

The problems, as mentioned, are based on some bad decision-making in urban planning back centuries ago.  This have been exacerbated by climate change – meaning lack of drinking water for many and the potential to lead to health issues, mass migrations to other cities, or conflict, which will be played out around the globe.  This example of non-coastal impacts of climate change is one of the most interesting aspects of the story, as much attention has been placed on sea-level rise but less on inland communities.  “Mexico City — high in the mountains, in the center of the country — is a glaring example. The world has a lot invested in crowded capitals like this one, with vast numbers of people, huge economies and the stability of a hemisphere at risk.”

One way this phenomenon is visible is in the architecture, with subtle rolling building forms as seen below creating waves of differential settlement.   An animation of the process shows the action creating this building form, due to differential layers of volcanic soils and clays, which drain and hold water at dramatically different rates.

What happens when the water is drawn down creates instability reflected in the constant sinking and retrofitting of buildings.  Kimmelman explains the impacts: “Buildings here can resemble Cubist drawings, with slanting windows, wavy cornices and doors that no longer align with their frames. Pedestrians trudge up hills where the once flat lake bed has given way. The cathedral in the city’s central square, known as the Zócalo, famously sunken in spots during the last century, is a kind of fun house, with a leaning chapel and a bell tower into which stone wedges were inserted during construction to act more or less like matchbooks under the leg of a wobbly cafe table.”

Aside from the quirky buildings, there are major issues throughout the region, more pressing as climate change increases.  Kimmelman mentions that “development has wiped out nearly every remaining trace of the original lakes, taxing the underground aquifers and forcing what was once a water-rich valley to import billions of gallons from far away.”  That conveyance of water is so difficult, that many residents are unable to get water easily, especially from taps.  This has led to an economy of ‘pipas’, “large trucks that deliver water from aquifers” to fill tanks.  Approximately 40% of residents get water this way.

The other issue is the difficulty of removing sewage and drainage, again because of geology and topography, along with leaks and inefficiencies of the aged infrastructure.  The Grand Canal is no longer able to gravity flow, described as “wide open, a stinking river of sewage belching methane and sulfuric acid”.  Pump stations are installed to assist this, and the canal, albeit ‘visible’ is marginalized, traveling under roadways and being polluted via impervious surfaces along the way.

While portions of the Grand Canal are still visible, the hidden hydrology and it’s implications, heightened by climate change, are evident in sinking buildings, lack of drinking water, and substandard infrastructure, a trifecta of issues that come back to the origins of a water based city from seven centuries back.  I mention long history, and this is a lesson in how quickly the decisions of the past can turn on us with population growth and a changing climate.

Per Kimmelman: “The whole city occupies what was once a network of lakes. In 1325, the Aztecs established their capital, Tenochtitlán, on an island. Over time, they expanded the city with landfill and planted crops on floating gardens called chinampas, plots of arable soil created from wattle and sediment. The lakes provided the Aztecs with a line of defense, the chinampas with sustenance. The idea: Live with nature.” 

The idea at the time, and even today is valid, but the modern challenge is confirmed by Loreta Castro Reguera, “a young, Harvard-trained architect who has made a specialty of the sinking ground in Mexico City, a phenomenon known as subsidence” who was interviewed in the article.

““The Aztecs managed. But they had 300,000 people. We now have 21 million.”

Xochimilco

A follow up from features the further story of the hydrology of Xochimilco, a UNESCO World Heritage Site that was covered by Victoria Burnett in a February 22nd story “An Aquatic Paradise in Mexico, Pushed to the Edge of Extinction” This article picks up the thread of the canals and islands from the original settlement.  “With their gray-green waters and blue herons, the canals and island farms of Xochimilco in southern Mexico City are all that remain of the extensive network of shimmering waterways that so awed Spanish invaders when they arrived here 500 years ago.”

The article focuses on the impacts of water usage in the region, with water from Xochimilco being pumped to other areas of the city, creating sink holes and draining canals which threaten the livelihoods of farmers and tourism industries.   The canals have long supported both industries, and also include wetlands and the infamous farming techniques called chinampas, which date back to Aztec era, and include ‘floating gardens’ in the shallow lakes.  A photo of these from 1912 show the this in action:

The article discusses the residual impacts of development on the aquifers, which impacts the regions waterways, but also, similar to the previous article, creates subsidence that impacts buildings and sinkholes.  The visible whirlpool in January lowered the water level quick enough to cause alarm before it could be stopped.

The water tourism in the area, typified by the trajineras, a blinged out local gondola, has been impacted as well.  One of the operators takes heed of the omens of water, stating:

“Nature is making us pay for what we have done”

In additional to development (building on the chinampas), there is pollution of the canals themselves, which has jump-started some efforts to reduce water use of the aquifer through rainwater harvesting, but the immensity of the problem of supplying water for a region with 22 million people is massive.  The balance between providing water and maintaining the cultural heritage means the possible loss of knowledge of chinampa farming, as well as health issues for locals.  This could quickly become irreversible, unless action is taken, as mentioned by Dr. María Guadalupe Figueroa, a biologist at Autonomous Metropolitan University, who ends the article: “…without a serious conservation effort, the canals will be gone in 10 to 15 years. But much of the damage was reversible, she said, adding: “It’s still a little paradise.”

Invisible Rivers

The two articles reminded me of a couple of articles I had filed away for future posts.  With the interest piqued from the above coverage, I dove into a 2016 CityLab post “Mexico City’s Invisible Rivers” which focuses on the work of Taller 13 and their plans to “uncover the 45 rivers that flow under the Aztec capital, hidden underground for decades.”  The first phase involves the Piedad River, and the idea of daylighting 9.3 miles of the corridor. shown in some detail below (with many more images on their site via the link above or via an online document here).

There’s a lot of similarity to the Cheonggyecheon River in Seoul (mentioned here in the Lost Rivers documentary post) in terms of the final look and feel as well as the transformative potential, as mentioned in the article by urban biologist Delfín Montañana”

““This project shatters paradigms. It proposes to tear down a private road, which you cannot use unless you have a car. What we propose is that we remove the cars, open the pipes, and treat the water. We need to transform the model of our city”

The hidden gem in the post is the document “La Ciudad de México 1952 1964” published by the Departamento del Distrito Federal. México,  This document outlines the public services of the city, including chapters on water and sewer that have some great info (with, in my case, some translation).

Sections on potable water and drainage show ‘modernization’ along with maps of these systems (of passable by not great quality).  The following shows the drainage system of the time, which involved a lot of pipes and images of pipes being built, and people in pipes.

A colored map of the historic Mexico from the document takes us full circle, to the hydrological history, a city literally built on a lake, economies as well built on that watery foundation, and now dealing with the consequences.