**3. Context of the groundwater crisis in Mexico**

In this global context, Mexico will face several challenges given the simultaneous pressures of population growth, urbanization, climate variability, and climate change [13]. Mexico's population will reach near 148 million people in 2050, which means an increase of 23% concerning 2015 [14] while the urban population will increase by 35.7 million in 2050 [15]. These increases will escalate the demand for food, energy, products, and services, with the consequent augmentation of water demand. Additionally, population growth has an unfavorable distribution concerning water availability because 77% of the population is established where 33% of available water is found [16].

Moreover, Mexico's climate has been classified as semi-arid to arid, and as a result, and particularly in the northern half of the country, we are continuously experiencing droughts of different magnitudes [17] and with climate change, an increase in their severity and frequency can be expected [18]. Besides, because of the latter, a decrease in cumulative precipitation is expected [19] and positive anomalies of temperature [20] in Mexican territory. Temperature changes will boost water demand, mainly for the environment and food production, while changes in precipitation and runoff

### *The Usefulness of System Dynamics for Groundwater Management DOI: http://dx.doi.org/10.5772/intechopen.105162*

point to a decrease in water availability [18]. Actually, in the RCP 6.0 scenario, a reduction between 16 and 25% in precipitation is expected in the northern region of the country, while in the northeast a reduction up to 40% is anticipated [21]. Climate change impacts at the basin scale have been documented previously. For example, in Herrera-Pantoja and Hiscock [22] it was suggested that surface runoff in the Rio Queretaro basin can decrease 9.16%, while in Molina-Navarro et al. [23] it was reported that reductions of 45% in the short term can be anticipated in runoff of the river Guadalupe basin, in Baja California.

In this context, groundwater but me managed strategically because it looks more resilient to rainfall variability caused by climate change [21], and besides, it may mitigate drought effects [24]. In fact, in the National Program Against Drought (Pronacose, in Spanish) of the Mexican water authority Conagua, the exploitation degree of aquifers was selected as an indicator of adaptation capacity to compute climate vulnerability [25] and for example, in the watershed-scale program against drought of the Rio Balsas basin council, three of the five strategic measures related to water supply involve groundwater [26].

It is worth mentioning that, in general, groundwater has advantageous properties concerning other water sources: lower evaporation losses, protection of contamination caused by human activities, flexible management of the resource, and wide spatial distribution [27]. However, despite these features and their relevance in the current climate context, Mexican aquifers are severely affected. Aquifers' overexploitation and overallocation characterize current water management [28] and if this trend prevails, the resilience of human systems to water shortages will be compromised [29]. Nationally, groundwater supplies 35.5, 58.6, and 56.3 of water demand for irrigation, public urban, and industrial use, respectively [30]. By consequence, in Mexico, groundwater has a critical role in water security and its depletion can compromise food security, environmental security, health, and economic development.

There are several definitions of overexploitation [27]. Conagua defines it as the condition where the ratio of extraction to mean annual recharge is greater than 1.10. In Mexico, there are 105 overexploited aquifers [25], which represent 16.07% of all aquifers and are illustrated in **Figure 4**. It might sound like a small fraction, however, these overexploited aquifers and supply sources for the most important urban and industrial centers in Mexico, and around 42 million inhabitants depend partially on them [31], as shown in **Figure 5**. By consequence, despite that the national balance of groundwater is positive (i.e., 92.5 km3 of recharge and 29.9 km3 of extraction in a year), some local balances are not [25].

Additionally, overallocation, which refers to the assignation of groundwater volume assignation beyond the resource availability, is a product of the miscalculation of the mean annual availability of aquifers [28]. This indicator is computed by subtracting the compromised natural discharge and the recharge from the allocations; the former is defined as compromised water for surface allocations or environmental purposes [32]. In 2020, it was reported that nationally 92.4 km3 of recharge occurred, and 42.9 km3 were compromised as natural discharge; hence, there were 49.5 km3 of availability, and 41.5 km3 were allocated. That means that 83.1% of mean annual availability was allocated [33]. However, it is worth highlighting that the mean annual availability of 275 aquifers is negative, which reflects the phenomena of overallocation. Is it interesting to underscore that 7 of the 10 aquifers with less availability are found in the state of Chihuahua: Los Juncos, Laguna de Santa María, Laguna de Tarabillas, Laguna de Hormigas, Lagunas la Vieja, Jiménez-Camargo, and Meoqui-Delicias; their availability is found between −697.79 and −165.04 km3 .

**Figure 4.** *Overexploited aquifers in Mexico. Reproduced from Conagua [25].*

#### **Figure 5.**

*Metropolitan zones in Mexico. Reproduced from Conagua [25].*

It is worth mentioning that the compromise of the drinking water supply is not the only consequence of aquifers' overexploitation. This has also caused spring discharge depletion, disappearance of lakes and wetlands, decrease of base flow in rivers, elimination of native vegetation, and ecosystems loss [27]. This represents serious affectations. Firstly, intensive extraction of groundwater can alter the quality through the upwell of thermal and/or mineralized water of underlying aquifers and the infiltration of organic contaminants from sewage and rainfall percolation [34]. Similar contamination is widely documented in Mexico. For example, in Camacho et al. [35] there was a report of arsenic occurrence in Chihuahua and Coahuila states in

### *The Usefulness of System Dynamics for Groundwater Management DOI: http://dx.doi.org/10.5772/intechopen.105162*

concentrations higher than permissible. And if that was not enough, besides meaning a public health risk, overexploitation and pollution of aquifers also have an impact in groundwater dependent ecosystems. For example, in Esteller and Diaz-Delgado [36] it was reported that the ecosystem of the Almoloya del Río wetland had been affected by the overexploitation of the Valle de Toluca aquifer. Finally, the overexploitation of aquifers can explain subsidence in urban areas, which has important implications for infrastructure and buildings operation and maintenance. Possibly the best known case is that of Valle de Mexico, but there is also evidence for Aguascalientes [37] and the cities of Tepic, Nayarit [38]; Celaya, Guanajuato; Morelia, Michoacán; and Queretaro, Queretaro [39].
