Mexico City is digging in to prepare for a wetter—and rapidly sinking—future. Like Jakarta and New Orleans, much of the metropolis of twenty-two million is literally falling under the weight of its own growth. A century of unrelenting groundwater pumping has led to runaway land subsidence, with no clear short- to medium-term solution.1 This undermines the city’s combined sewers and drainage canals (which carry stormwater and sewage together) even as the climate crisis brings more frequent and intense rainstorms. In response, the government has undertaken ambitious tunneling projects to drain the city. While initially transferring the city’s flooding problems elsewhere, they are themselves unlikely to be sufficient to weather the storms to come. This means that the city’s streets will continue to flood. The key political question, however, is whose streets will bear the brunt of this flooding. 

While flooding patterns owe much to local rainfall distribution, topography,2 and the design of infrastructures, policymakers and the public in cities around the world frequently overlook the ways the operation of drainage infrastructures exacerbates the effects of already inequitable flood protection for marginalized residents. Mexico City’s long struggle against flooding shows not only how the operation of drainage systems exacerbates inequity but also points to ways more equitable operating protocols might be implemented to effectively socialize not just the costs of flooding (as is often done through insurance schemes), but the spatial distribution of floodwaters themselves. 

The Mexico City metropolitan region is built largely on a series of artificially drained lakes in a closed basin with no natural rivers flowing in or out. Decades of excessive groundwater extraction have caused the city to sink, rendering major drainage canals nearly useless. The region therefore depends instead primarily on one of the world’s largest and most complex deep drainage tunnel systems to artificially drain water from the basin every time it rains. These tunnels—ranging between four and seven meters in diameter—snake deep underneath the city and capture water from both the city’s rivers and local sewers, which themselves carry a toxic mix of sewage, industrial waste, and—during storms—rainwater. The system, known as the Deep Drainage System (Sistema de Drenaje Profundo), is like a subway network for stormwater and sewage, which nearly every inhabitant depends on, but no one sees. 

The system’s primary tunnels were inaugurated in 1975 and immediately reduced flooding in downtown Mexico City, which had previously faced regular and catastrophic floods. Nevertheless, the city’s subsequent growth rapidly outpaced the government’s expansion to the system. This growth meant that even typical storms (occurring multiple times a year) would generate far more stormwater than the system could handle. The core problem was that the government had expanded the urban area served by the tunnel system without expanding the capacity of the system’s backbone: its outlet conduits, which gathered the entire system’s water and ejected it from the watershed entirely. 

As a result, these outlets increasingly became bottlenecks during heavy storms, which caused backups throughout the drainage system. By 1999, the system was in a generalized crisis, as evidenced by a disastrous overflow of water from an oversaturated drop shaft of the tunnel, which flooded Ejército de Oriente, a working-class neighborhood on the city’s eastern periphery. In the wake of a series of similar disasters, government engineers began to carefully ration access to the drainage system to avoid letting it become oversaturated. This improvised operational practice had previously been largely unheard of; the engineers who built the system did not imagine—or design—the system to operate in this way.

Engineers rationed access to the system primarily through the closure of floodgates that control the flows of sewers into the drainage tunnels. Much like metering the onramp to a freeway, the closure of floodgates caused backups of sewage and rainwater into local neighborhood sewers, routinely resulting in floods. This process of rationing was, however, highly political. Under pressure from politicians, engineers would routinely leave floodgates open in the richest and most central parts of the city—allowing them priority access to drain their waters—while closing floodgates in the poorest peripheral neighborhoods. This operational practice often meant “sacrificing” these neighborhoods—a phrase engineers themselves often used—to floods of up to a meter (and sometimes even more) of sewage and rainwater. These neighborhoods served as de facto detention basins to temporarily hold stormwater that protected the rest of the city from more intense flooding. 

The human and material toll of these floods was severe, as they would regularly triple commute times, cause infections, and ruin homes for residents with little or no savings. Some residents were forced to invest in extraordinary adaptations like meter-tall floodgates for their doorways, while others simply abandoned their first floors during the rainy season.3 Due to these recurrent floods, these neighborhoods became sacrifice zones: areas the government disproportionately exposed to toxic health effects and property damage—not to mention psychological trauma—in order to protect the health and wealth of more privileged areas of the city.4 

In 2019, the government inaugurated a new outlet tunnel that promised to reduce the drainage system bottleneck and therefore the necessity of such rationing and the associated floods in the metropolitan region. Known as the Eastern Outfall Tunnel (Túnel Emisor Oriente), this tunnel has largely succeeded in reducing backups (and therefore the need to ration access) in the metropolitan drainage system even if smaller floods still occur due to local drainage network incapacity. Nevertheless, this project has simply displaced the problem of flooding elsewhere, farther from the city: the tunnel is now centrally implicated in a flood in September 2021 that killed fourteen and gravely affected thirty thousand residents in the Mezquital Valley, where it discharges Mexico City’s waters.5 Both to avoid such downstream floods and deal with increasingly intense storms due to climate change, the government will soon need to ration access to the drainage system once again. If left uncontrolled, the city’s continued expansion into undeveloped areas will also generate more stormwater, similarly accelerating a return to rationing.

Nevertheless, there is no reason that such rationing must necessarily disproportionately sacrifice the poor, as has been the historic government practice. A more equitable approach to managing rationing during these critical storm events would be to close the floodgates of the city’s tunnel system in a relatively even pattern designed to induce widespread flooding across the city’s vast low-lying region (which includes much of the wealthier city center), rather than simply in its poorest peripheral neighborhoods. Spread over wider areas, floods might be kept within manageable depths of ten to twenty centimeters, which could be easily contained with minor adaptations of doorways and driveways. The result of such an equitable rationing of access to the city’s drainage system would mean that more of the city would flood on a given night with a heavy downpour, but the actual level of floodwaters would be much lower for everyone. 

The result of such a redistribution of floodwaters would be the creation of what we might call collective sacrifice zones. The term recognizes that environmental harms produced by collective forms of life (e.g., cities) should be borne collectively, by spreading environmental harms across the population as broadly and equitably as possible.6 “Equitable” here does not mean equal, however. Indeed, equity would demand closing the floodgates (and therefore risk flooding) in those areas with the greatest wealth first and disproportionately, precisely because they are the zones where residents and businesses have the most means to adapt to and recover from flooding—and these are also the areas that have long benefited disproportionately from the system’s discriminatory operations. Rather than forcing the poor to adapt first and most radically to a changing environment, equity demands that those with the most means to adapt be first in line to receive the brunt of increasingly severe disasters.

The physical design of the city’s drainage infrastructure does not prevent city engineers from rationing access more equitably. The fact that they do not do so (despite, ironically, often being from the very same neighborhoods that are regularly flooded) has everything to do with the political pressures they face to protect the wealthiest parts of the city from flooding, whose residents can threaten the state with costly lawsuits out of reach of poorer residents. The only way to reverse this tendency is to collectively organize and build the popular power to pressure the state to operate the system more equitably, despite almost certain opposition from the residents and business owners of the city’s wealthier urban core.

To be clear, the operational strategy described here should be a recourse of last resort. It does not diminish the urgent need for new and expanded infrastructures to separate, retain, and reuse stormwater, as well as a deliberate slowing of the city’s growth via a national decentralization strategy that channels investments away from Mexico City.7 Nevertheless, it will take years for such decentralization to bear fruit, and building infrastructures of the scale needed to completely eliminate flooding is impractically costly. This means that severe storms will continue to overload the drainage system. Yet while flooding may be inevitable in such circumstances, the inequitable distribution of floods across the space of the city is far from preordained. A change in operations could produce a far more equitable distribution of flooding in the city during such rain events.

Designers and policymakers in cities elsewhere have much to learn from Mexico City’s inadvertent experiment with managing a drainage system pushed far beyond its normal operating capacity. Mexico City’s drainage system is, of course, unique: it has controls built into it—and a network-wide interconnectivity—that allow for the relatively straightforward and precise redirection of water throughout the system, even when it is overwhelmed. Not every city has (or could develop) a similar level of control over their floodwaters, but for those that do, it is essential to examine how these systems might operate differently. These operations may well be the key to socializing flooding, such that it is no longer the poor who bear the disproportionate burden of adapting to a rapidly changing environment.

  1. Estelle Chaussard et al., “Over a Century of Sinking in Mexico City: No Hope for Significant Elevation and Storage Capacity Recovery,” Journal of Geophysical Research: Solid Earth 126, no. 4 (April 2021), https://doi.org/10.1029/2020JB020648 ↩︎
  2. In areas of the city with rapid land subsidence, “topography” is not a constant, but a constantly varying product of local geology and the history of groundwater extraction ↩︎
  3. For more on this history and these operations, see Dean Chahim, “Governing Beyond Capacity: Engineering, Banality, and the Calibration of Disaster in Mexico City” American Ethnologist (forthcoming) ↩︎
  4. The term “sacrifice zone” is typically used somewhat more narrowly to describe communities (disproportionately poor and, in the US context, inhabited by people of color) living alongside toxic industries, military installations, and their waste, whose well-being is sacrificed in the name of broader political and economic objectives. See Steve Lerner, Sacrifice Zones: The Front Lines of Toxic Chemical Exposure in the United States (Cambridge, MA: MIT Press,  2010). The kind of sacrifice I am describing here is more intermittent—floodwaters come and go—but residents face much of the same ongoing health effects and trauma and are similarly stuck in place ↩︎
  5. Dean Chahim, “La Tragedia de la Inundación en Tula fue una Decisión Política,” Washington Post, September 20, 2021, https://www.washingtonpost.com/es/post-opinion/2021/09/20/tula-inundaciones-rio-causas-hidalgo-mexico ↩︎
  6. Referring to toxic contamination, Lerner (2010, 300) puts it this way: “If sacrifices must be made for the greater economic good in a democratic republic, then surely they should be evenly shared.” ↩︎
  7. For examples of the kinds of structural changes needed to improve water management in the basin, see Centro para la Sustentabilidad Incalli Ixcahuicopa, Repensar la Cuenca: La Gestión de Ciclos del Agua en el Valle de México (Mexico City: Universidad Autónoma Metropolitana, 2009). https://agua.org.mx/wp-content/uploads/2009/05/Repensar-la-cuenca-La-gestion-de-ciclos-del-agua-en-el-Valle-de-Mexico.pdf ↩︎