Hydrogeologic Setting
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Mexico City Aquifer located in the Valley of Mexico City, a closed basin between volcanic ranges (Figure 1) that serves as the principal source of groundwater for the metropolitan area, which supports over twenty-two million people (Palma Nava et al., 2022). In the past, the basin was covered with multiple lakes, including Lake Texcoco, Lake Xochimilco, and Lake Chalco, which formed a large connected system that played an important role in the reginal hydrology by storing and slowly releasing water to the subsurface (Chavez Guillen, 2007).
Figure 1. The aquifer extents within the Mexico City Basin in blue and the aquifer area in red. The basin is surrounded by a volcanic mountain range with elevations up to 5201 meters above sea level (masl). (Image from Palma Nava, 2022).
Regional Climate
This region experiences a subtropical climate, with a wet season starting in May through October and a dry season from November through April (Ruiz, 2015). Annual precipitation ranges from 600 to 1200 mm, with most rainfall precipitating in the summer months, shown in Table 1 (Ruiz, 2015). The seasonal rainfall accounts for the aquifer recharge through infiltration and surface runoff (Palma Nava, et al., 2022). However, city expansion has led to lower infiltration and natural recharge rates (Palma Nava, 2022).
Table 1. Monthly average temperatures and precipitation in Mexico City from 1991-2021 (Climate-Data.org).
Month Average Temperature (℃) Precipitation (mm)
January 13.4 26
February 15.1 23
March 16.7 32
April 18.4 53
May 18.7 83
June 17.6 159
July 16.4 171
August 16.5 166
September 16 183
October 15.1 108
November 14.1 37
December 13.7 17
Mechanisms of Aquifer Recharge
Recharge mechanisms of the aquifer come from direct infiltration of rainfall, seepage from rivers and lakes, and the mountains surrounding the basin (Ruiz, 2015). Isotopic studies have shown that the mountains are the main recharge zones, containing groundwater dating from the Pleistocene (Palma Nava et al., 2022). Due to lower groundwater levels, Manage Aquifer Recharge (MAR) has been introduced to artificially recharge the aquifer using methods such as infiltration basins, injection well, and stormwater harvesting, shown in Table 2 (Cruz Ayala, 2020).
Surface water
Humans have significantly altered surface water in the basin. Most of the lakes have been drained for human consumption, yet remnants such as the Xochimilco canals, and the wetlands continued to stay hydrologically connected to the aquifer (Chavez Guillen, 2007). In addition to the remnants of ancient lakes, rivers such as the Rio Magdalena, Rio Mixcoac, and Rio Churubusco had contributed to the hydrological network of the basin (CONAGUA, 2010). These rivers were part of the natural drainage and recharge system, but now these rivers have been canalized or diverted due to urban expansion (CONAGUA, 2010). These features are part of the recharge mechanism but are minimal due to the larger consumption of groundwater for urban consumption and the loss of natural recharge zones (C40 Cities, 2019).
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