Did you know Mexico City is built on a drained lake system that covered around 1500 square kilometers surrounded by mountains?
During earlier times the Aztecs used to live around the shores of these lakes and developed an efficient terraced agricultural system that used irrigation canals and dykes for its water resources. These canals and dykes apart from supplying water, also acted as natural flood control systems. The Spanish conquest in 1519 resulted in hydraulic disruption of the region which eventually led to the draining of the lake and building of the City (Cifuentes, E., & Rodriguez, S. 2005).
In their article, Downs, Mazari‐Hiriart, Domínguez‐Mora and Suffet (2000) look back at the Chinampa irrigation method that employed canals and flood gates for their agricultural purposes which produced the surplus food that enabled the Aztec culture and civilization to flourish in this area. Although the Aztec civilization had an abundance of water, because of development of Mexico City, the area is under threat of depleting its aquifer. The aquifer supplies most of the water requirements for the City and its 20 million residents. Sixty percent of the water supplies come from wells that go into the aquifer which is currently being overexploited.
The depletion of the aquifer has even led to subsidence in different parts of the City and has caused the City to sink unevenly (Connolly, 1999). Miller and Spoolman (2012) also corroborate this in their book by stating that “Mexico city built on an old lakebed has one of the world’s worst subsidence problems because of increasing groundwater overdraft. Some parts of the city have sunk as much as 33 feet.” Currently, the urban demand of 60 percent is met by exploiting groundwater at 1.6 times the recharge rate and less than 10 percent of wastewater is treated and reused inside the local basin (Downs, Mazari‐Hiriart, Domínguez‐Mora, & Suffet, 2000). Mexico City is also a flood prone area especially since it is located within a closed hydrological basin and it gets heavy rains over short periods. The average rainfall in Mexico City is about 800mm (Tortajada, 2006).
In June 2000, 80 hectares of urbanized land of the Chalco Valley located within the MCMA was inundated with waste water as a result of the La Compania sewage canal breakage, affecting many low income inhabitants in the area. More than 6,700 households were affected by gastrointestinal, skin and waterborne diseases. Electricity and water supply were cut-off and food supplies were also affected (Aragon-Durand, 2007).
Mexico City’s drainage system is such that storm water, industrial effluent and sewage all go down the same drain which is then pumped out of the valley (Connolly, 1999). The water supply and drainage systems have not only become very large and complex, but also obsolete in many areas.
Other than the many problems that exist in the water supply system, one major problem is that about 40 percent of the water is lost in the network due to leakage, aged piping, lack of maintenance and illegal connections. It is estimated that the lost water, if saved, could provide supply for up to 4 million people every day.
Another injustice is wealthy areas use up to 600 liters per capita per day while poor areas use up to 20 liters per capita per day (Tortajada, 2006). In light of the flooding, water resource and supply problems that are facing the City, certain solutions can be adopted to improve the situation.
The first step that can be taken is to maintain the mountains that surround Mexico City, as they are islands of biodiversity that play a major ecological role and affect the hydrologic cycle. Miller and Spoolman (2012) cite an example of China’s Yangtze River watershed which flooded in 1998 and killed at least 15 million people, not to mention the economic losses. It was identified that deforestation in the region was one of the main causes. Drawing from the experience of this event, it would be wise to prevent any deforestation of mountain slopes around Mexico City. A campaign and program to reforest the surrounding mountains would not go wasted. Downs, Mazari‐Hiriart, Domínguez‐Mora and Suffet (2000) point towards an optimistic option of renovating Zumpango and Texcoco, the two ancient lake bodies within the basin to capture rainwater and to store excess runoff making it to work as a reservoir. Further initiatives to recycle waste water for secondary uses must also be considered.
Another initiative could be to maintain the watersheds and the wetlands in the basin as they could provide numerous free services such as filtering toxic wastes and pollutants, reducing flooding and erosion, recharging aquifers and maintaining biodiversity in the region (Miller & Spoolman, 2012). A similar system of water ways and wetlands already exists, but is under threat. They are the Chinampas of Xochimilco, Mexico City. The Chinampas used to be highly productive traditional wetland agricultural systems which fed most of the population during pre-hispanic times.
Chinampas are small strip shaped islands forming a network of canals built with mud, branches and decaying vegetation. They hold the soil within plots and also act as wind and insect barriers. Recognizing their aesthetic and cultural value, Chinampas were declared part of a world heritage site by UNESCO in 1987.
There is a strong trend to substitute these Chinampas with plastic greenhouses for flower production as it is economically more viable. While these greenhouses achieve higher economic benefits in the short term, Chinampas provide a very valuable ecosystem service. Chinampa owners do not receive any economic incentives or benefits from UNESCO or the government and as a result are under the risk of extinction due to land use change. The value of these Chinampas must be recognized by the authorities and policies and incentives put in place to protect them, especially since Mexico City is a heavily polluted area with very limited green spaces (Merlin-Uribe, et al., 2013).
Another initiative that could protect the Chinampas is to develop these areas into eco-tourism hotspots which could bring sufficient economic returns to incentivize maintaining them.