Summary and Regional Overview

Mexico City was originally known as Tenochtitlan in the 14th century, and it was built as a fortified settlement on the islands of Lake Texcoco (Figure 1). Originally a city of islands and canals, it has expanded significantly over the centuries, particularly after the foreign influence of colonization, which has required the construction of extensive water drainage systems to reduce flooding. The current geographical extent of Mexico City encompasses areas throughout the Valley of Mexico (Valle de México), and in the southern half of the city, up the Neo-Volcánica slopes (Britannica-a, 2022).

Figure 1: A map of the water bodies that formed the foundation of the Aztecs heartland (left) and the artist’s mural of what Tenochtitlan would have looked like, circa 1500 (right). This mural hangs in the National Achaeological Museum and shows that the foundation of Mexico City are dug right into the lakebed, coexisting with the water of Lake Texcoco. Image source: RocDoc (2016).

In 2016, Mexico City transitioned from being a federal district to an administrative region with similar autonomy as a state, following an amendment of the federal constitution. As of 2023, Mexico City, also known as CDMX (Ciudad de México in Spanish, México in Nahuatl), has a population of almost 9 million people and an area of 573mi2, making it the largest municipality in North America (ADIP, n.d.). The metropolitan region has a population of almost 23 million, making it the largest Spanish speaking city in North America and being similar in size to the New York – Newark metropolitan population of 24 million people (ADIP. n.d. World Bank, 2020. WPR, 2023). Mexico City is bordered to the north, east and west by the state of Mexico, and its metropolitan area spreads into the Valle de México. To the south, Mexico City is bordered by the state of Morales (Figure 2).

Figure 2: Google Maps imagery showing the relative position of Mexico City and a zoomed-in view of CDMX and the Valle de México. The shaded area of the zoomed image denotes the expansion of CDMX’s urban core (Source: Google Earth Imagery & zoomed image by Yavidaxiu (Spanish original), Redx360 (English translation) – Wikipedia).

Mexico City has a subtropical highland climate, classified as Cwb in the Köppen climate classification system. The average annual temperature lies between a range of 0°C and 20°C, with at least 4 months of daily temperatures consistently above 10°C (Figure 3). In Mexico City, seasons are characterized as being primarily wet or dry, with the winter months being dry season and the summer months having at least 10 times as much rain (ClimateData, 2022). Over centuries, Mexico City has recorded climate variations that lead to alternating extreme weather events like drought, and floods (Lankao, 2010).

Figure 3: A graph showing the climate of Mexico City in 2022. The blue bar graph indicates precipitation, in mm or inches, and clearly shows a focus of increased rainfall in the summer months (July – October). The red line indicates the average monthly temperature, which collates to 16°C for the average year. Finally, note the altitude at 2238m above sea level. Image source: ClimateData (2022).

Mexico City’s annual average temperature is unusually cool for a city located in the tropics, owing to its elevation and the mountains that border it to the south, east and west. Due to this geography, the city experiences dry, mild winters with maximum temperatures sometimes peaking above 20°C. During the summer months, the intense heat is ameliorated by the rain, which keep the temperature cooler with minimums that mirror winter averages, as well as helping the air with moisture and cleanliness (Britannica-a, 2022).

When originally established, the city was surrounded by a mixture of saline and freshwater lakes, which helped to moderate temperatures and increase humidity. However, the proximity to water also created flooding concerns during the rainy season, particularly with little natural drainage channels due the mountainous geography (Tellman et al. 2018). Drainage projects to dry the soil and reduce flooding risk began in the early 1600s, and these were moderately successful. The agriculture system was impacted by reduced water levels, but it survived with enrichment of foreign seeds and new farming techniques (Aztec-history-a, n.d., Jiménez et al. 2020).

In the early 1900s, the grand canal project was initiated. Throughout the next half century, the development of wastewater, sewage, and drinking water infrastructure in Mexico City improved local flooding protection. However, this infrastructure also created challenges for the city’s agriculture system by sourcing from local springs, removing the muddy subsoils, and draining and drying the local Xochimilco wetland areas (Jiménez et al. 2020).

Groundwater serves as the primary source for Mexico City’s residential, agricultural, and commercial water needs. This is problematic, as overexploitation of groundwater sources has impacted the stability of the city’s physical foundation. Internal pressure of the aquifers have dropped with constant over-use, and the weight of the city has resulted in subsidence issues and concerns (CDMX, 2019).

The water systems of Mexico City are under heavy strain, primarily as a result of overpopulation and urban sprawl. City and population expansion has increased reliance on dwindling groundwater reserves. The results are issues of subsidence, aquifer collapse, industrial damage, and an increasing reliance on treated wastewater instead of freshwater (Figueroa et al. 2022. Tapia-Villaseñor et al. 2022). Compounding the issue is industrial and agricultural expansion, which has resulted in water contamination from agrochemicals and byproducts. Such pollutants degrade crops, damage ecosystems and biodiversity, and pose threats to public health (Zambrano et al. 2009. Alvarez-Moya et al. 2022). Furthermore, climate change is drying and warming the climate, further increasing water requirements and hastening desiccation of the Xochimilco wetland system.

Regional Description

History

In 2015, a national census found that 21.5% of people living in Mexico self-identify as Indigenous, most of which live in the south-central and southern regions of the country. About 6.5% of this population, or roughly 7.8 million people, speak an Indigenous language (INEGI, 2015. MRG, 2018. Schmal, 2019). Nearly 24% of Indigenous language speakers speak Nahuatl, which is the principal language of the Aztec empire or the Mexicas of Tenochtitlán empire.

The Aztec empire is considered to be the last great Mesoamerican civilization before the influence of foreign culture on this part of Turtle Island (North America)(History, 2009. ELA, n.d.). Roots of the Aztec empire can be traced to the early 14th century, where it flourished in the Valle de México. The Spanish conquistadors invaded in the early 16th century, bringing foreign diseases which devastated indigenous populations (Oldstone, 1998). Through alliances with local tribes that were opposed to Aztec rule, the Spanish maneuvered their forces and political influence, resulting in the capture of Tenochtitlan, the capital of Aztec civilization (History, 2009).

Preceding the Aztecs, the earliest known civilization in Mesoamerica is the Olmec culture, which can be traced back to as early as 1500 BCE. The Olmec peoples were based in the lowlands around the gulf of Mexico after its inception in Soconusco, Veracruz (Pool & Loughlin, 2017). The first major Mesoamerican culture to flourish in the Valle de México, with influences from the Olmec peoples, was the Tlatilco civilization from roughly 1250 BCE to 800 BCE. Around 250 years after its inception, the style of artwork seems to have rapidly changed from Olmec to a more original and central-american native style, possibly indicating a change in faith practices (Betton, 1987. Koontz, 2015).

Tlatilco culture was overtaken, in terms of regional prevalence and dominance, by the city and culture of Cuicuilco, which began as a farming village and now exists in the Tlalpan borough in CDMX as a historic monument (Cartwright, 2016). From 800 BCE to 150 CE, the village grew to a city of 20,000 people, and it is believed to have formed the sociocultural foundations for the Altepetl city states, which formed the Aztec empire (Corral, 2014. Encyclopedia, 2023a). Around 50 BCE, the Xitle volcano scattered the Ciuciulco culture, destroying most of the buildings and dispersing the Ciuciulco people to nearby settlements. Many Altepetl city states developed subsequently, and through this development emerged Altepeme, that is, local areas of social, cultural and economical management with buildings dedicated to worship and markets. The Altepeme became sites of multi-ethnic meeting areas that were managed by a local ruler or council, who also often controlled taxation. Eventually, through many peoples, such as the Nahuas, Altepetl grew into civilizations such as the Mayans (Lockhart, 1992. Encyclopedia-b, 2023).

The 1895 national census of Mexico included the first record of languages spoken following the country’s independence in 1821, and over 2 million Indigenous speakers were identified, with almost 650,000 of these being Nahuatl speakers (INEGI, n.d., Connolly, 2003). The Federal District (i.e., what is now CDMX) and the state of Mexico were home to 174,478 Indigenous language speakers. In the state of Mexico, 44,427 of the 158,335 people identified that they spoke Nahuatl (28.1%). In the Federal District, 15,605 of the 16,143 Indigenous language speakers spoke Nahuatl (96.7%; INEGI, n.d. Schmal, 2019). The 1900 census recorded a population of the Federal District at 541,546 people, which means, roughly 3% (16,143 of 541,546) of the region spoke an Indigenous language, with the vast majority being Nahuatl speakers (INEGI, n.d.). In the 2015 census, it was recorded that 8.8% of its 8.86 million inhabitants of the Federal District self-identify as Indigenous, and 1.5% of its population, almost 133,000, speak Nahuatl (INEGI, 2015. Schmal, 2020).

Water systems and infrastructure

Mexico’s 2030 Water Agenda (produced in 2011) identifies that the country uses approximately 78.4 billion m3/year, with 11.5 billion m3/year of that usage being unsustainable (CONAGUA, 2011). Of the country’s 653 aquifers, 105 of them are considered to be overexploited and used at unsustainable levels (Tortajada, 2006). Mexico City was estimated to have a groundwater extraction rate of 507,364 million m3/year and only 279,026 million m3/year infiltrating to refill, making the city one of the country’s most significant sites of aquifer overuse (García-Soriano et al. 2020).

A 2014 report from the Mexican Institute of Water Technology estimated Mexico City’s agricultural land to be 6.4 million hectares (Mha), with 3 Mha being irrigated through groundwater sources. Agriculture is responsible for 77% of the water consumption in CDMX, with the remaining consumption attributed to public (15%) and industrial (6%) usage (IMTA, 2014). These proportionate levels of consumption have remained relatively consistent over the last decade.

Xochimilco is within the area formerly covered by Lake Texcoco during the days of the Aztec empire, the primary remaining waterbody being Lake Xochimilco (Figure 4)(Tellman et al. 2018). Despite its designation as a world heritage site, Xochimilco’s ecosystem and agricultural land is highly threatened (Pérez-Belmont et al. 2021). Informal settlements, declining water quality and quantity, and invasive species are among the many factors that have led (and are continuing to lead) to declines in ecological health and agricultural viability (Mazari-Hiriart et al. 2008).

Figure 4: A map of Xochimilco that outlines water bodies, the chinampera, and highlights the overwhelming urban growth. The zone of chinampas is intricately woven with canals, and is a part of the UNESCO designated RAMSAR site. Image source: Kok (2016).

After completion of the grand canal in the 1950s and 1960s, water diversion impacted the canals of Xochimilco and necessitated an immediate boost to water levels. The regional administration tried to compensate for these issues by redirecting partially treated wastewater to the wetlands; however, this impacted water quality, and after significant public pressure, the city’s first wastewater treatment plant was developed to restore water quality (Figueroa et al. 2022). Redevelopment of the chinampa agriculture system (chinampera) and market was further slowed by increasing competition, thanks to imported foods shepherded in after greater road connectivity. Over the next decade, the chinampera grew until it connected with the urban center, both creating a tourist attraction, and spreading usable water alarmingly thin. Reports show a portion of the chinampera becoming saline during this period, affecting agricultural productivity and reducing the potential opportunities for agricultural workers (Jiménez et al. 2020).

Ecology

CDMX is composed of 16 boroughs (Figure 5), known as alcaldias. Xochimilco, ‘the lungs of Mexico city’, is an urban wetland that spans roughly 2,600 hectares of floodplains and canal systems (Rubio et al. 2020). For the people of Mexico City, Xochimilco provides food, water, and cultural values, as well as serves as an economic hub for tourism and mercantile business (Kenza et al. 2018. Roa-Fuentes, n.d.). 

Figure 5: An image showing the boroughs of Mexico City. The orange region outlines the modern era political boundary of CDMX, whilst the darker orange portion in the middle denotes the original city of Tenochtitlan. The water bodies shown are the 5 lakes that were mostly drained, following the expansion of Mexico City after foreign influence (García-Soriano et al. 2020).
Image credit: Frapaise, (2020).

In 2004, the United Nations Educational, Scientific and Cultural Organization (UNESCO) designated 2,657 hectares of the Xochimilco ecosystem as a protected area and World Heritage Site. Under the Ramsar convention, the area is protected to preserve the cultural heritage of Xochimilco’s chinampa system and endangered species such as the axolotl salamander, as well as to bring awareness to degradation of the site via effects like eutrophication and pollution (Ramsar, 2004).

There are over 1,100 protected species in Mexico, roughly 900 of which are considered threatened, and nearly 500 deemed endangered (Olivera, 2018. EarthsEndangered, 2023). Among these is the critically-endangered and culturally-important axolotl, which was recently chosen as the national emoji of Mexico and is the only salamander in the world that can regenerate full limbs and organs (Sokol, 2018). The species has experienced significant population decline significantly over the last 25 years, to 0.00005% of their original population. Major threats and pressures on their populations include introduced fish species that feed on young axolotl, such as tilapia, perch and carp. Other threats include the declining health of the aquatic ecosystems in central and southern Mexico due to agrochemical runoff, wastewater mismanagement and overfishing (Bluereef, 2020).

Through the chinampera and the wetland network, Xochimilco provides various benefits such as unique habitats for threatened species, climate and air stabilization, as well as plays a significant role in carbon sequestration (Ebel, 2019). The local temperature would rise by at least 2℃, and air quality would drop significantly if CO2 emissions and particulates in the air were not filtered by the agricultural network. (Rubio et al. 2020).

Agriculture

One of the most sustainable and productive agriculture systems in the modern era are the chinampas of Mexico City (Pérez-Belmont et al. 2021). The first recorded use of chinampas pre-dates the Aztec empire; however, the rapid expansion of the Aztec civilization demanded improved planning and mechanical engineering to sustain growth of this food production system (Pell, 2017. Gayatri, 2022). Chinampas are situated in the shallow lake beds of water systems around Mexico City, and they are built up over time with compost and mud (Figure 6). Chinampas were around 30 meters long and 2.5 meters wide, and stakes and willow trees were used to stabilize the edges and protect them from the erosion of the canal waters (Fagan, 2019). The chinampas shaped their surrounding canals, giving them the illusion of floating islands used for crops.

Long term water storage and preparation systems such as dams and sluice gates were put into place to maintain optimal water levels for chinampas with seasonal change. In addition, the Aztecs developed fertilizer systems that utilized human waste, involving the use of canoes to transfer excrement down the canal-ways, and such an approach effectively integrated wastewater management and agricultural production (Nichols & Rodriguez-Alegria, 2016). The chinampa agriculture system in CDMX has the potential to provide food for roughly 8 million people, however, due to degradation, 95% are currently unused (DHWTY, 2014).

Figure 6: Chinampas shown in context. The posts provide stability while the willow tree roots grow through to the canal bed and form a tough exterior on the outer edge of the chinampa to protect them from erosion. As the plot is constructed to act like a sponge, it absorbs the nutrient rich water of the canal system continuously, such that the crops grow rapidly and can be harvested multiple times per year, as long as they are maintained (DHWTY, 2014. Britannica-b, 2022). Image credit: DHWTY, 2014.

Due to their land and resource efficiency, chinampera are an excellent example of the potential that Indigenous knowledge and food production techniques have for contributing to sustainable food systems. Another is the terraced gardens system implemented in Aztec times, which involved developing arable land on inclines with minimal damage to ecosystems (Salem, n.d.). The terraces were built with irrigation ditches to maintain rich soils, and crops cultivated in these spaces used the three sisters system of squash, maize and beans that supports a healthy nutrient balance (Aztec-history-a, n.d.). 

Many great foods and treasured ingredients of the world originated from Mexico. This includes chocolate, which was first cultivated by the Olmec people thousands of years ago (Garthwaite, 2015). Later, during Mayan times, chocolate took on a spiritual and ceremonial quality and was often mixed with chillies, another important cultural food (Festa, 2020).

Avocados, tomatoes, chillies, the nopal cactus (Nopales), and the three sisters crops have become the cornerstone of Mexican cuisine. Indigenous communities were also able to use chinampas to catch and add animal species to their diet, such as waterfowl, frogs and fish. Additionally, the highly prized algae was farmed in Lake Texcoco, a food product that is now known referred to as spirulina (Aztec-history-b, n.d.).

Meat was not a significant part of Mexican diets historically; however, there are some notable culturally-significant food species, such as the acocil, a crayfish species, and the axolotl, a salamander that represents the god: Xolotl. Meat became a more prominent part of the Indigenous Mexican diet after the Spanish introduced cheese, garlic, beef, pork, chicken and onions (Aztec-history-c, n.d.).

Potential and existing disruptions to water security

Overpopulation

The urban expansion of Mexico City poses logistical problems for providing water to its sizable population. Capture and transportation of water has become increasingly expensive due to the lack of available sources and increasing maintenance costs (Banister & Widdifield, 2023). The growing demand on groundwater stresses freshwater resources and the Xochimilco ecosystem (Kok, 2016).

In the 19th century, following the drainage project, the wetland’s water sources were diverted to supply the masses in Mexico City, which subsequently contributed to the degradation of the Xochimilco wetland. As the chinampera system became increasingly drier, water was pulled from a wastewater treatment plant to nullify and reverse system decline. However, this treated wastewater lacks the appropriate nutrient content and quality for effectively supporting the ecosystem (Mazari-Hiriart et al. 2008. Figueroa et al. 2022). 

Groundwater is the primary water source for Mexico City, and through rapid growth, aquifer reserves have emptied without time to recuperate. In 2020, measurements from the Santa Cruz River aquifer indicated a >75% drop in sustained pull since 1993, from 36.4 million m3/year to less than 8 million m3/year (Tapia-Villaseñor et al. 2022). Unsustainable use and loss of groundwater can lead to aquifer collapse, for which the best remedy is prevention, as reversing the damage is difficult and expensive (CDMX, 2019). Compounding this issue is infrastructure damage such as pipe leaks in water distribution systems, which places greater draw on sources due to water loss (CDMX, 2016). As the issue worsens, subsidence will become a greater structural threat, and potable water availability will continue to decrease.

Overpopulation and large-scale development also exerts stress on the physical foundations of Mexico City. Roads and buildings have slowly tilted, becoming wavy or unstable, and entire sections of the city are sinking due to the soft grounds on which Mexico City was built. This makes seismic activity a particular threat as the unstable ground is already compromising infrastructure stability, which is only exacerbated by the overexploitation of groundwater sources (Wei-Haas, 2017).

Climate Change

Mexico is currently experiencing one of the most severe droughts in recent history (Figure 7), with over 85% of the country suffering from drought related water loss since late 2019 (Patel, 2021). In the last 600 years, Mexico has suffered over 130 droughts (Mendoza et al. 2005). These are preceded and followed by often disastrous flooding events, aggravated by deterioration of drainage systems during heat waves (Lankao, 2010).

Figure 7: An image of the Villa Victoria Reservoir, taken in March 2020 (left), and again in March 2021 (right). Extreme drought is visible in the sediment buildup over time, due to lack of water, and the paler surrounding landscape. Image Source: Joshua Stevens (Nasa Observatory, 2021).

Funding issues mitigate effective reparations to drainage and flood protection systems, which in turn perpetuates the cycle of water loss through infrastructure damage. Funding issues also mitigate effectiveness of water storage solutions, which worsen the effects of drought (Ezcurra et al. 1999).

Industrial and Agrochemical pollution

Water pollutants are a major cause for concern in the Xochimilco wetlands. Agrochemicals like fertilizer and pesticides combine with industry effluent and sewage, both liquid and solid forms. These pollutants contaminate agricultural and drinking water, which already consists of high portions of treated wastewater, resulting in water unfit for agriculture and human consumption (Olson, 2008. Zambrano et al. 2009. García-García et al. 2012. Alvarez-Moya et al. 2022).

There are over 1,400 points of drainage into Mexico City’s water systems, including wastewater dispensation, industry effluence, uncontrolled landfill seepage, agrochemical runoff, municipal water discharge and more (Olson, 2008). Water samples from Xochimilco during a research study showed contamination in over 90% of results, with the majority of attribution to human and animal bacterium (Zambrano et al. 2009). Due to the weight of the city applying pressure and reshaping the landscape, some of the water that originally left the city through the grand canal now flows backwards, thereby concentrating contamination in Mexico City’s water supplies (Tellman et al. 2018).

Nitrogen and phosphorus pollutants from fertilizers bring excess nutrients to the Xochimilco canal system, resulting in the proliferation of aquatic weeds and the attraction of pest species. When the weeds dry and fall to the canal bottom, they decompose and add organic refuse in the system (Zambrano et al. 2009). The chinampera system is reliant on carefully maintained water levels and quality, as the chinampas act like sponges for the canal water that sustains the crops. Chinampera degradation thus accelerates water quality issues, as the lower water quality spurs the dying crops that litter the canals (Mazari-Hiriart et al., 2008; García-García et al. 2012).

The use of pesticides is prevalent to protect crops around Mexico City, in part due to the degradation of the canals. Pesticide chemicals infiltrate water supply, presenting health threats to terrestrial and aquatic organisms from glyphosate poisoning (Alvarez-Moya et al. 2022). 

Invasive species

Water hyacinth, native to South America, is a vascular aquatic plant that competes with native aqua-culture in CDMX. Its rapid growth and tendency to form thick mats can clog waterways, hindering agriculture and making transportation difficult for mercantile activity or tourism. Additionally, in the over-stimulated canal systems of Xochimilco, where issues with over-saturation of plants and debris are already a pervasive issue, water hyacinth causes eutrophication, provides habitat for pests and blocks sunlight for water-based bacterium (Rocha-Ramírez et al. 2014; Bohling, 2016). 

Current initiatives and efforts

“A water resilience plan for the heritage zone of Xochimilco, Tlahuac and Milpa Alta” was released in 2019 that analyzes key vulnerabilities and threats, investigates water resources and assesses solutions for a healthier and more resilient water system in the specified areas. The scope of the project is grounded in regional and local reporting, modeling and assessment, with the goal of creating a future plan for implementation of realistic and non-invasive solutions (CDMX, 2019).

“Resilient flood management for Xochimilco, Mexico City” is a thesis written by Alexander Karel Kok in 2016, that focuses on handling the foundational issue of flood management, the same issue that has plagued Mexico City for centuries. Xochimilco is a crucial region of the city for socio-economic and cultural reasons that requires a significant amount of water to function, however, with higher water levels, concurrent flood risk to Xochimilco and surrounding regions needs to be addressed.

Future Outlook

Mexico City is facing critical water issues regarding groundwater exhaustion and reliance on treated wastewater to subsidize industry, agriculture and domestic usage. Compounding issues, such as subsidence, desiccation of wetlands and pollution, make solving these issues complex and expensive, especially considering the millions of citizens that rely on these services and resources. The CDMX has several plans in place which, when implemented in concert, may provide an avenue for progress toward healthier water systems.

“A water resilience plan for the heritage zone of Xochimilco, Tlahuac and Milpa Alta” is a comprehensive, multi-organization strategy guide that aims to build resilience of some of Mexico City’s most critical water systems. The general objective is to restore the systems to working order, to such an extent that the self-perpetuating issues noted above are no longer causing unchecked degradation, as well as future proofing the water systems against climate change and increasing socio-economic pressures.

The “CDMX Resilience Strategy” is another multi-organization, inter-departmental strategy that aims to create a management system that fosters inclusive and adaptive public policies, in which the city can face numerous future risks without impeding development. The vision is to create a united Mexico City that can face the mounting pressures of the 21st century without stalling economically, environmentally or socially.

“The 2030 Water Agenda” is a document produced a year after world water day in 2010, where Mexico committed to consolidating water policies by 2030 to enable sustainable development and make progress toward a cleaner country for the next generation. The aim is to protect the nation’s water bodies, reduce pollution and provide universal access to safe, clean water, as well as reduce flooding risk in vulnerable areas.