Mexico City sits in a closed mountain basin where a network of shallow lakes once covered the valley floor. Over roughly five centuries, human activity has drained those lakes, pumped the aquifer dry beneath them, paved the exposed lakebed, and packed the basin with more than 20 million residents. The result is one of the most radically altered landscapes on Earth, with consequences that extend from the ground literally sinking underfoot to the near-extinction of species found nowhere else.
The Lakes That Disappeared
The single most dramatic transformation was the deliberate destruction of the Valley of Mexico’s lake system. Before Spanish colonization, several interconnected lakes filled much of the valley floor. The Aztec capital of Tenochtitlán was built on an island in Lake Texcoco, the largest of them. Colonial authorities, eager to prevent the chronic flooding that plagued the city, embarked on centuries of drainage projects. By the twentieth century, Lake Texcoco had dried up almost completely, and the basin had been re-engineered into what researchers describe as a “megabasin” in which water is shuttled from distant sources to serve the urban region and then drained away again to prevent floods.1Land. Water Diversion in the Valley of Mexico Basin: An Environmental Transformation That Caused the Desiccation of Lake Texcoco
The dry lakebed did not simply sit there quietly. For much of the twentieth century, it generated dust storms that choked the city. Government officials and residents treated these storms as an ordinary nuisance, not an environmental crisis. It was not until international bodies began reframing what counted as “air pollution” in the late 1960s and early 1970s that the connection between the desiccated lakebed, industrial smog, and automobile exhaust was taken seriously as a public-health problem.2Sage Open. The Development of Air Pollution in Mexico City
A City Sinking Into Its Own Foundations
Draining the lakes solved the flooding problem but created a new one. With the surface water gone, the rapidly growing city turned to groundwater. Mexico City now depends mainly on a regional aquifer for its water supply, and that aquifer sits beneath thick layers of highly compressible clay, the soft sediments left behind by the vanished lakes. Pumping water out of the aquifer compacts those clays, and the ground above drops. One recent study measured total settlement of about 3.7 meters at one monitoring site, averaging roughly 30 centimeters per year.3Groundwater for Sustainable Development. Land subsidence in Mexico City: New insights from field data and numerical modeling
Across the city more broadly, subsidence rates reach up to 50 centimeters per year in the worst-affected areas. An analysis integrating over a century of ground-level surveys with satellite radar and GPS data found that these rates have held roughly constant since at least 1950. Critically, the study showed that almost no elastic rebound occurs when pumping slows, meaning the sinking is essentially irreversible. The researchers estimated it will take about 150 more years for the upper clay layer to finish compacting, during which the ground could drop by an additional 30 meters in some zones.4Journal of Geophysical Research: Solid Earth. Over a Century of Sinking in Mexico City: No Hope for Significant Elevation and Storage Capacity Recovery
The consequences of this sinking are everywhere. Water and sewer pipes crack, buildings tilt, roads buckle, and the drainage system that was built to move water out of the basin loses its gradient, sometimes flowing backward. Subsidence also reshapes how earthquakes hit the city. The soft lake clays amplify seismic waves, which is a major reason the 1985 and 2017 earthquakes caused such devastating damage in specific neighborhoods. Research on the seismic behavior of these high-plasticity clays confirms that the old lakebed sediments respond to shaking in ways hard rock does not, turning moderate ground motion into something far more destructive at the surface.5Soil Dynamics and Earthquake Engineering. Seismic response of high plasticity clays during extreme events
Trapped Air and Persistent Smog
Mexico City’s geography would challenge air quality even without heavy industry and millions of cars. The city occupies a basin surrounded by mountains on nearly all sides, which generally prevent polluted air from venting away. Daily industrial activity, transportation, and other urban emissions release gases and particulate matter that either harm health directly or combine in sunlight to form secondary pollutants like ozone and fine particles. The result is a metropolitan area highly prone to poor air quality, sometimes severe enough to trigger government-imposed environmental contingencies that restrict activity.6Atmospheric Environment. Circulation patterns influencing the concentration of pollutants in central Mexico
The city has tried policy interventions. The most famous is Hoy No Circula (“No Driving Today”), a program launched in 1989 that restricts which vehicles can be driven on which days based on license-plate numbers. An impact evaluation of the program found that its initial implementation and later modifications produced short-term decreases in carbon monoxide and nitrogen oxide concentrations, but those gains were followed by increases over the medium and long term.7Semantic Scholar. Is the Remedy Worse Than the Disease? An Impact Evaluation of Mexico City’s Flagship Air Pollution Control Program One widely discussed explanation is that many families simply bought a second, often older and dirtier, car to get around the restrictions. The episode illustrates how human modifications to one part of the environment can trigger behavioral changes that undercut the intended fix.
The Urban Heat Island
Replacing lakes, wetlands, and agricultural land with concrete and asphalt changes how a city absorbs and radiates heat. Mexico City has experienced a measurable urban heat island effect that has grown in both spatial extent and intensity as the population swelled from roughly 12 million to over 20 million and the built-up area expanded from about 1,050 to over 1,600 square kilometers.8Academia. The actual urban heat island in Mexico City Nighttime temperatures in the densest urban core can be several degrees warmer than in the surrounding countryside, affecting energy use, water demand, and human comfort. Because the city already sits at a high elevation (about 2,240 meters) with relatively mild temperatures compared with lowland tropical cities, residents sometimes underestimate how much the local climate has shifted. But the trend is clear: more pavement, fewer trees, and less water all push temperatures up.
Xochimilco and the Vanishing Axolotl
In the southern part of Mexico City lies Xochimilco, the last remnant of the pre-colonial canal and lake system. For centuries, farmers here used chinampas, floating garden beds built from layered vegetation and lake mud, to grow food. These wetland agricultural plots were so productive they fed most of the population in pre-Hispanic times. But modern land-use change has taken a heavy toll. Research documents a loss of roughly 2,500 hectares of chinampas, largely replaced by plastic greenhouses used for commercial flower production. Although the greenhouses are more profitable, they eliminate tree cover, fill in canals, and stop providing the food or ecosystem services the chinampas once did.9Academia. Environmental and socio-economic sustainability of chinampas (raised beds) in Xochimilco, Mexico City
The most famous casualty of Xochimilco’s degradation is the axolotl, a salamander found naturally nowhere else on Earth. Wild axolotl populations have been dramatically reduced and now persist only in isolated pockets of the canal system.10Biological Invasions. Food web overlap among native axolotl (Ambystoma mexicanum) and two exotic fishes: carp (Cyprinus carpio) and tilapia (Oreochromis niloticus) in Xochimilco, Mexico City The threats are layered: urban expansion has eaten away at surrounding land, greenhouses have replaced open fields, and the water itself has been invaded by non-native fish such as carp and tilapia that compete with axolotls for food. A connectivity analysis found that once you account for urban sprawl, greenhouse expansion, and the loss of cropland and grassland, the area actually suitable for axolotl habitat restoration shrinks to less than 40 square kilometers.11Urban Ecosystems. A connectivity analysis to find areas for habitat restoration of the axolotl (Ambystoma mexicanum) in its natural habitat
A recent environmental DNA survey of Xochimilco’s waterways painted a grim picture: the wetland is now a low-diversity ecosystem dominated by alien fish species. Researchers found no genetic evidence of axolotls at any wild sampling site, detecting them only in a managed wildlife refuge. The study characterized Xochimilco as a “severely degraded wetland” and emphasized the role refuges play in preventing total extinction in the wild.12Environmental DNA. Persisting at the Edge of Ecological Collapse: The Impact of Urbanization on Fish and Amphibian Communities From Lake Xochimilco The axolotl has become an international symbol of conservation, with captive breeding programs worldwide, but the animal’s survival in its actual home waterway hangs by a thread.
Where the Wastewater Goes
A city of this size produces enormous volumes of sewage, and Mexico City’s disposal strategy has environmental consequences that reach far beyond the basin. Much of the city’s wastewater flows north through a massive drainage system and ends up in the Tula Valley in the state of Hidalgo, one of the world’s largest agricultural areas using wastewater for irrigation.13PubMed. Delivering on sustainable development goals in wastewater reuse for agriculture: Initial prioritization of emerging pollutants in the Tula Valley, Mexico Historically, much of this wastewater arrived untreated. About half of the irrigation water infiltrates into the ground and reaches aquifers from which local communities extract drinking water.14Environmental Pollution. The removal of microorganisms and organic micropollutants from wastewater during infiltration to aquifers after irrigation of farmland in the Tula Valley, Mexico
The long-term result is contamination. Studies of soils irrigated with Mexico City’s wastewater have found that certain heavy metals, including chromium, cobalt, and copper, are present at levels considered potentially hazardous. Copper shows up not just in the soil but in plants at concentrations that exceed toxicity thresholds.15Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. Heavy metal accumulation in plants and soil irrigated with wastewater from Mexico city In effect, the city has exported part of its pollution problem. New wastewater treatment capacity has come online in recent decades, but the legacy contamination in soils and aquifers will take much longer to address than the time it took to create it.
Forests and Green Space Under Pressure
Mexico City’s southern and western edges include forested hills that serve as critical watersheds, recharging the very aquifer the city depends on. These peri-urban forests face deforestation, unplanned urban sprawl, and environmental degradation. A study modeling land-use change in four southern watersheds found that infrastructure development is the most important driver of forest loss, and under a business-as-usual scenario, forest cover will continue to decline over the next two decades.16PubMed Central. Forest fates: Unraveling the peri-urban social-ecological trajectories in Mexico City’s conservation land This creates a vicious loop: removing forests reduces aquifer recharge, which deepens the water deficit, which intensifies pumping, which accelerates subsidence.
Inside the city, green space is both scarce and unequally distributed. Research has found that access to urban green space is directly correlated with demographic features common in lower-income neighborhoods, aligning with environmental justice concerns that urban amenities are distributed inequitably against more marginalized populations.17EconomÃa, sociedad y territorio. Inequitable distribution of green public space in Mexico City: an environmental injustice case A separate analysis during the COVID-19 pandemic confirmed the pattern statistically, finding a strong relationship between a neighborhood’s poverty level and whether residents had access to green space within walking distance. The poorest groups were significantly less likely to have a park or green area within 300 meters.18Urban Forestry & Urban Greening. Rethinking the distribution of urban green spaces in Mexico City: Lessons from the COVID-19 outbreak In a city where heat, air pollution, and stress are pervasive, who lives near a tree and who does not matters for physical and mental health.
What Survives in Urban Parks
Despite all the damage, Mexico City’s remaining green spaces still support surprising biodiversity, particularly for birds. A study spanning 31 green spaces across the city, from natural protected areas to manicured parks, found meaningful variation in bird diversity depending on how transformed each space was. Less-modified areas with native vegetation hosted more species and a wider range of ecological roles than heavily landscaped parks.19Frontiers in Ecology and Evolution. Taxonomic, Phylogenetic and Functional Diversity of Bird Assemblages in Urban Green Spaces
A more recent survey of nine urban parks recorded 108 bird species, five of which are under special protection status. Park size and noise pollution emerged as the two most influential variables shaping which birds showed up. Seed-eaters and omnivores tolerated noisy environments, while insect-eaters and fruit-eaters preferred quieter areas with denser vegetation.20Birds. Influence of Park Size and Noise Pollution on Avian Species Richness in Urban Green Spaces: A Case Study from Mexico City The practical takeaway is that protecting larger parks and reducing noise around them does more for biodiversity than simply counting the total square meters of green paint on a city planning map. Habitat quality, not just quantity, determines what can survive in a landscape this heavily shaped by human hands.