Mexico City, one of the world’s most expansive megacities, is situated within a unique geographical basin at a high altitude. This distinctive setting, surrounded by mountains, has profoundly influenced its development and the environmental changes it has experienced. The city’s rapid growth has introduced complex environmental challenges.
From Lake to Megacity: Historical Environmental Shifts
Mexico City’s origins trace back to the Aztec capital, Tenochtitlan, built upon a system of lakes. This historical foundation significantly shaped the region’s environmental trajectory. Following the Spanish conquest, lakes were drained for urban expansion and flood control. This transformed the landscape, replacing natural water bodies with urban infrastructure and agriculture.
This historical alteration of the hydrological cycle has had enduring consequences. The city sits on a soft, clay-rich lakebed, and the draining initiated land subsidence. This ongoing subsidence continues to affect the city’s infrastructure and its ability to manage water.
The Challenge of Air Pollution
Human activities have degraded Mexico City’s air quality. Vehicle emissions are a primary source of air pollution, with millions of cars circulating daily. Industrial activities also contribute pollutants from factories and power plants. The city’s mountain basin topography traps pollutants, hindering their dispersal and creating a “bowl effect.”
Common pollutants include ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen oxides. Ozone forms from photochemical reactions in the city’s high altitude and intense sunlight. While air quality has improved since its peak in the 1980s and 1990s, concentrations of ozone and particulate matter often remain above acceptable standards.
Managing Water Resources: Scarcity and Subsidence
Mexico City’s growing population and industries strain its water resources. The city relies on groundwater from aquifers for much of its water supply. Over-extraction has led to water scarcity, necessitating the import of water from distant sources like the Cutzamala system.
Groundwater depletion directly causes land subsidence. As water is pumped from the soft, clay-rich lakebed beneath the city, the soil compacts, causing the city to sink. Some areas have experienced subsidence rates of up to 20 inches per year, damaging infrastructure like roads, buildings, and the metro system. This sinking also complicates wastewater management and can worsen flooding during heavy rains, as the altered landscape affects drainage.
Urban Sprawl and Waste Management
Mexico City’s urban growth has significantly altered its surrounding environment. Urban sprawl has converted natural habitats, agricultural lands, and green spaces into developed areas. This expansion contributes to biodiversity loss and reduces ecosystem services, such as groundwater replenishment.
The large population generates thousands of tons of solid waste daily. A large portion, potentially up to 90%, ends up in landfills. Managing this volume is difficult, as the city has limited disposal sites and transfers waste to neighboring states. Landfills emit methane, a potent greenhouse gas, and can lead to soil and water contamination.