Saline intrusion assessment using the GALDIT index on the northern coast of Quintana Roo, Yucatan Peninsula, Mexico

Access to drinking water is recognized as a basic human right, a central objective in global, national, and regional agendas in which Mexico participates. In this context, any discussion of water and its management also involves human rights, development, health, and social equity (UN 2015; Furey 2018; CONAGUA 2020). From the perspective of salinity, the World Health Organization (WHO) defines drinking water as water with a concentration of less than 1 gram per liter (g/L) of total dissolved solids (WHO 2011).

In coastal areas where freshwater is supplied from an aquifer, saline intrusion is particularly relevant, being a process resulting from the contamination of freshwater by increased salinity due to physical or anthropic factors or a combination of both. Pressure and overexploitation of water resources have different social, economic, and environmental impacts, especially in coastal urban areas where more citizens are directly exposed (Post & Werner 2017; Kim et al. 2022). Several previous studies showed evidence that coastal zones are highly vulnerable to pollution and salinization, which combined with other pollutants such as nitrogen species, metals, and coliforms, represent a challenge to pollution management, sustainable water use, and community involvement in safeguarding coastal habitats, biodiversity, and water sources (Nguyen & Huynh 2023; Nguyen et al. 2023; Sukri et al. 2023).

The north coast of Quintana Roo is a complex case facing major conflicts and sociopolitical contradictions associated with its physical and social characteristics (Romero Martínez 2015; CONEVAL 2020). This region is experiencing multiple spatial processes that respond to significant changes in land use and inequalities in socio-economic conditions due to massive tourism dynamics, which have led to an exponential increase in water consumption since the 2000s (Romero Martínez 2015; Deng et al. 2017; CONEVAL 2020). The growing needs of the population and services in the presence of a saline interface affect the quality of the ‘Yucatan Peninsula’ aquifer. This aquifer is susceptible to contamination from human activities, combined with the natural hydrogeological conditions, as detailed below (Deng et al. 2017; Canul-Macario et al. 2021; CONAGUA 2021; Chandrajith et al. 2022).

The aquifer located in northern Quintana Roo is part of the Yucatan Peninsula aquifer (3105), formed by sedimentary rocks of the Tertiary and Quaternary periods (Butterlin & Bonet 1963). This aquifer flows radially toward the coast, showing preferential zones in the Holbox fault located parallel along the coast in the northern portion of Quintana Roo (Bauer-Gottwein et al. 2011; Gondwe et al. 2011). The aquifer is of the free type in the recharge and transit zones, while it is usually confined in the discharge zone, reflected as springs in the coastal zone (Bauer-Gottwein et al. 2011). A sharp interface between the regional aquifer and seawater is observed, where the freshwater layer becomes thinner toward the coastal zone (Moore et al. 1992; Stoessell & Coke 2006).

The thickness of the freshwater layer and the position of this mixing zone in the aquifer, also called halocline, are sensitive to hydrological stressors such as hurricanes, tides, decreased recharge, and increased mean sea level. These direct effects of climate change represent major challenges for coastal urban settlements, as they involve unfavorable climatic and hydrological conditions for the management of coastal aquifers (Parra et al. 2016; Coutino et al. 2017; Kovacs et al. 2017, 2018; Young et al. 2018; CONAGUA 2021; Salata et al. 2022).

Other relevant factors are groundwater exploitation through pumping and recharge induction processes, which are the most common causes of saline intrusion or seawater intrusion (SWI), defined as the inland movement of seawater in coastal aquifers arising from the imbalance between boundary conditions and the position of the freshwater–seawater mixing zone (Bear 1979; Werner 2017). However, understanding these processes should not be limited to local hydrogeology but should also include the socio-economic and ecological functions of local groundwater systems, as well as their interactions with other natural systems and human activities, to make reliable diagnoses and optimal decisions on groundwater resource management policies and measures (Van der Gun 2018).

It should be stressed that almost all human activities in the region are supplied by the aquifer. As a result of the characteristics of the soil, the nature of the subsoil, the high permeability and infiltration in the terrain, and the scarce relief in the Yucatan Peninsula, there are scarce surface currents in the south that serve as water supply sources for the population (CONAGUA 2021; Bautista 2023). Therefore, studying saline intrusion into this aquifer is essential for the water, food, and energy security of the different freshwater-dependent systems and the ecosystems affected by increased groundwater salinity (Post & Werner 2017).

From a demographic perspective, in 2020, Quintana Roo tripled Mexico's annual population growth rate of 1.2% (INEGI 2020). The highest rate was recorded in the municipality of Solidaridad, where the city of Playa del Carmen is located, with 7.9%, followed by Tulum with 5.3% and, in third place, the municipality of Benito Juarez. The main settlement in the latter is the city of Cancun, showing the highest growth rate and the largest population in Quintana Roo, with 911,503 inhabitants (INEGI 2020). Other factors that have increased in recent years are poverty, extreme poverty, and social deficits in the population (CONEVAL 2020). By 2050, an increase exceeding 64% in the population and its inequality gap is estimated in the region compared with 2020 (INEGI 2020; CONAGUA 2021). This projection is relevant because this indicator is associated with high levels of vulnerability and, in this case, access to and cost of drinking water and sewage services. According to data for 2018 from the National Tariff System, the state of Quintana Roo had the most expensive fees for these services in the Yucatan Peninsula (CONAGUA 2024).

The maximum water extractions for the entire Yucatan Peninsula aquifer in 2020 occurred on the north coast of Quintana Roo, with 907.71 Mm³/year. Currently, water use is highest in the services sector, followed by the urban public sector, and, to a lesser extent, in agriculture, industry, and livestock raising (Table 1; CONAGUA 2021). Water is mainly used for the floating population of visitors to the state; the other important use is to supply the residents. Projections on population growth for 2050 show that this aquifer will be under high stress due to the increasing population and the demand for water in the service sector (Deng et al. 2017; CONAGUA 2021).

The coverage of the population with piped water supply in this region went from 88.7% in 1990 to 97.22% in 2020 (INEGI 2020). In this sense, the north of Quintana Roo there are 463,000 inlets, 94% of which are for household use, supporting a population of approximately 1,481,686 inhabitants in the municipalities of Benito Juarez, Isla Mujeres, Puerto Morelos, and Solidaridad. From 1994 to 2023, the region invested in 217 extraction wells, 71 drinking water tanks, 101 sewage pools, 3,250 km of water pipes, 2,157 km of sewage pipes, 3 reverse osmosis plants, and 13 wastewater treatment plants treating 31.5 Mm³ of wastewater per year (AGUAKAN 2023).

It is estimated that in 2050, the tourism sector, the main source of state income within tertiary activities that accounts for 85.7% of the Gross Domestic Product (GDP) (INEGI 2022), could extract up to 326% more of the available water if the current trends of total annual per-capita extraction are maintained. Therefore, the effects of saline intrusion may increase due to the lower levels of the associated coastal water table and a decrease in the Committed Natural Discharge,¹ and a decrease in recharge, thus compromising the water supply in this region (CONAGUA 2021).

There are methods to desalinate saltwater. However, desalination is the most energy-consuming water treatment method because saline and brackish water concentrate more pollutants than recycled or conventional water resources. This involves high costs for most inhabitants, high energy requirements, and significant environmental impacts. This option has been suggested as a partial solution to the current water supply system but not as the only water source in the region (Bell 2018).

Previous works on assessing saline intrusion in coastal regions include theoretical, analytical, experimental, and numerical approaches, recently implementing some intelligent methods for addressing these complex problems (Kharroubi et al. 2013; Deng et al. 2017, 2022; Alhumimidi 2020; Basack et al. 2022). However, detailed databases and technical information on saline intrusion in Quintana Roo are limited, making it difficult to understand the influence of this phenomenon on local groundwater systems.

The National Water Program 2020–2024 (CONAGUA 2020) and the Regional Water Program in the Hydrological-Administrative Region XII Yucatán Peninsula (CONAGUA 2021) remark on the saline intrusion implications in the water public supply of this region and the importance of developing research regarding this issue in Quintana Roo. Therefore, despite the existence of some regulatory instruments on water in the region (CONAGUA 2020, 2021), the context of saline intrusion in water management has not been fully addressed, which is crucial for the effective management of groundwater resources, and an essential component in the groundwater governance (Van der Gun 2018, p. 193).

The GALDIT index² can be used to identify regions that may be more exposed to saline intrusion. A region with a higher exposure has a higher probability of saline intrusion. Multiple studies at the global level show that this is a reliable methodology for generating elements that can assist and inform decision-makers about the effect of saline intrusion on coastal aquifers (Chang et al. 2019; Motevalli et al. 2018, 2019; Yang et al. 2022).

This study offers quantitative technical information that could be considered in future guidelines and decision-mark instruments, coinciding with the previously mentioned water instruments. Thus, considering the current water policies approach, this research meets the need to address the saline intrusion using pragmatic information supported by technical information, specifically within Quintana Roo state. Therefore, this research used the GALDIT index approach to assess the saline intrusion concerning the intrinsic aquifer characteristics of the northern Quintana Roo, providing maps that could be used, such as managing coastal groundwater resources and ascertaining the well-protected areas in the coastal belts for preventing saltwater mixing, and attending to the limited research developed on this important issue for the Caribbean region and Yucatan Peninsula described in the groundwater management instruments.

The GALDIT index calculated with the additive model in Equation (1) ranges from 2.5 to 10. A GALDIT index lower than 5 is interpreted as a low propensity to saline intrusion, a value between 5 and 7.5 indicates moderate susceptibility, and a value equal to or greater than 7.5 indicates a high propensity (Lobo-Ferreira & Chachadi 2005; Lobo-Ferreira et al. 2005).

This index was selected because it can be calculated using electrical conductivity (EC). The database was obtained from the National Water Commission studies in the region (CONAGUA 2001, 2005, 2006, 2013). An exercise was carried out with this dataset as a first approximation; however, it is important to continue monitoring these variables over time to follow their temporal evolution and not only spatially, as presented in this work. Similarly to the score ranges suggested by Chang et al. (2019), the following scores were established: 2.5 for EC values below 1,000 μS/cm, 5 for values between 1,000 and 2,000 μS/cm, 7.5 for values between 2,000 and 3,000 μS/cm, and 10 for values above 3,000 μS/cm. These ranges are proportional to the salinity from total dissolved solids established as permissible limits for drinking water (Secretaría de Salud 2000; WHO 2017).

Table 2 shows the categories of the GALDIT parameters and a detailed explanation of each index, providing the weight, range of variables, and importance classification of each parameter. The value ranges of the parameter are subdivided into four groups according to the site characteristics and the relative importance of the variable determined during the SWI evaluation described by Lobo-Ferreira & Chachadi (2005).

Components of the GALDIT index were rasterized in layers of 261 rows and 404 columns with a regular pixel size of 500 m × 500 m using Quantum Geographic Information System (GIS) (Qgis.org 2024). The resulting raster was projected to 16Q Universal Transversal Mercator (EPSG: 32616) with an extension defined by a lower coordinate of 396,204.17, 2,186,898.70, and an upper coordinate of 526,441.89, 2,388,667.02. The raster was processed using the Quintana Roo territory vectorial mask for better representation.

Particularly, inverse distance-weighted interpolation of the wells point vector was used to process the height of groundwater level above sea level (L), the impact of the existing status of SWI (I), and saturated aquifer thickness (T), considering a distance coefficient P fixed in 5.0. For groundwater occurrence (G), a rasterization conversion to the results of Kachadourian-Marras et al. (2020) using the Quantum GIS toolkit (Qgis.org 2024), considering a similar extension of the interpolation process. Distance from the coast (D) was calculated using a Quantum GIS toolkit buffer routine and later rasterized using a similar process to that used for the G index. Finally, aquifer hydraulic conductivity (A) is a constant value, as will be described in the next sections.

The type of aquifer is assigned a category depending on its hydraulic status. A confined aquifer is given the highest weight compared with partially confined and unconfined aquifers. The coast of Quintana Roo, and the Yucatan Peninsula in general, shows signs of confinement on the coast. This situation is supported by the fact that astronomical signals from the sea are reflected in the aquifer up to several kilometers inland, while these signals are rapidly attenuated in free aquifers (Ferris 1952; Trglavcnik et al. 2018; Coutino et al. 2021). Multiple investigations in the Yucatan Peninsula, and specifically in Quintana Roo, show evidence that marine effects are transmitted several kilometers inland (Parra et al. 2016; Tenorio-Fernández et al. 2016; Kovacs et al. 2017; Canul-Macario et al. 2020; Coutino et al. 2017, 2021; Pacheco-Castro et al. 2021). Finally, this confinement effect (ascending vertical gradients) coincides with the discharge zones defined by the regional flow systems (Toth 1963). In this sense, Kachadourian-Marras et al. (2020) described the regional flow systems along the entire coast of Mexico, considering that the zones defined as discharge for the Yucatan Peninsula will be indicative of confined aquifers, while the transit and recharge zones will be defined as unconfined aquifers.

Intrusion into an aquifer is affected by its hydraulic conductivity. Previous studies gave the highest propensity scores to hydraulic conductivity values above 40 m/day and the lowest to regions with hydraulic conductivity values lower than 5 m/day (Lobo-Ferreira & Chachadi 2005; Lobo-Ferreira et al. 2005; Chang et al. 2019; Yang et al. 2022). In this sense, the Yucatan Peninsula has a karst aquifer of high hydraulic conductivity with hydraulic conductivity values ranging from 10¹ to 10⁵ m/day (Bauer-Gottwein et al. 2011; Gondwe et al. 2011; Canul-Macario et al. 2021). This shows that the study area would always have the highest score; accordingly, it was assigned a weight value of 1, since, spatially, it would be a constant layer of score 10.

A freshwater aquifer with a high elevation above sea level (high hydraulic load values) is less susceptible to saline intrusion. This is explained by the fact that the hydraulic gradient is higher toward the coast; therefore, there is a discharge of fresh water that better controls the entry of saltwater into the continent. These conditions also make the aquifer less susceptible during rises in the average sea level (Ferguson & Gleeson 2012). This study used information on piezometric levels from aquifer monitoring networks provided by the National Water Commission for Quintana Roo (CONAGUA 2001, 2005, 2006, 2013). The network has a reference to the average sea level, ensuring that the levels used are representative.

Saline intrusion usually decreases with distance from the coast. Lobo-Ferreira & Chachadi (2005) determined that the perpendicular distance inland from the coastline and the height of the water table above sea level are the parameters with the greatest effect on the SWI potential and assigned them a maximum weight of 10. This study, similar to the literature consulted (Lobo-Ferreira & Chachadi 2005; Lobo-Ferreira et al. 2005; Chang et al. 2019; Yang et al. 2022), assigned a score of 2.5 to regions farther than 1,000 m from the coast and a score of 10.0³ to regions located less than 500 m from the coast.

This parameter considers the impact on existing salinity conditions in the aquifer. Lobo-Ferreira & Chachadi (2005) suggested that, initially, the molar ratio of chloride ions to bicarbonate ions (Cl⁻/[HCO + CO₃]) indicates the degree of SWI in a coastal aquifer in standard GALDIT studies. However, Chang et al. (2019) suggest using EC instead of the molar ratio or Cl⁻ concentration as a parameter of the GALDIT index. In coastal aquifers, this parameter is considered an acceptable indicator of the concentration of chloride ions in groundwater, which can be measured more easily and recorded in groundwater by CONAGUA (2001, 2005, 2006, 2013).

This parameter represents the thickness of a saturated aquifer. A thicker aquifer is affected by saline intrusion to a greater extent than a thinner aquifer. In this study, unlike the literature consulted, aquifer thickness was defined as the distance from the groundwater level to the saline interface, considering only the usable thickness of freshwater. In the Yucatan Peninsula, it has been observed that freshwater thickness toward the coast can vary between 15 and 5 m and show great variability throughout the coastline (Bauer-Gottwein et al. 2011; Gondwe et al. 2011; Moore et al. 1992; Stoessell 1995; Zamora-Luria et al. 2020). Aquifer thickness can be calculated using analytical models (Glover 1959; Lau 1967; Vacher 1988). In particular, the coastal aquifer of Quintana Roo shows an abrupt interface (Moore et al. 1992; Stoessell 1995; Bauer-Gottwein et al. 2011; Gondwe et al. 2011; Zamora-Luria et al. 2020), that is, the mixing zone between freshwater and saltwater is abrupt or shows a sharp interface, so analytical models such as Ghyben–Herzberg and Ghyben–Herzberg–Dupuit have shown an acceptable efficacy for calculating freshwater thickness (Bauer-Gottwein et al. 2011; Gondwe et al. 2011). The Ghyben–Herzberg model was used to calculate the aquifer thickness; this model calculates the depth of the saline interface H as 40 times the hydraulic load of the aquifer h. In this regard, aquifer thickness has been considered a variable that depends on the aquifer height level relative to the sea level. Considering the description by Lobo-Ferreira & Chachadi (2005), a region with an aquifer thickness greater than 10 m was assigned the lowest exposure score (2.5), while a region with a thickness less than 5 m was given the higher exposure score (10).

One limitation of the GALDIT index described by Kazakis et al. (2018) is that it cannot discriminate sources of salinization other than saline intrusion, such as groundwater contamination by surficial migration or chemical loads. These authors also explain that the GALDIT index is a good preliminary assessment that offers a holistic approach to coastal aquifers using its hydrogeological parameters.

Finally, the GALDIT index results were assembled (compared in a map) with the current vectorial urban information of the main coastal cities of northern Quintana Roo (Cancun, Playa del Carmen, Tulum), emphasizing the water supply polygons to evaluate which are exposed to saline intrusion, considering that zones with a high GALDIT index represent a propensity salinization condition.

Figure 1 shows the construction process of the GALDIT index applied to the north of Quintana Roo, considering the aquifer type (G), hydraulic conductivity of the aquifer (A), height of the water table above sea level (L), perpendicular distance inland from the coast (D), impact of existing SWI in the area (I), and aquifer thickness (T).

Some other zones with high salinity exposure stand out, such as the northern coast of Quintana Roo, in the Holbox zone, with GALDIT indexes reaching maximums of 8 in some areas, and the northern area of Playa del Carmen, with a maximum of 7.8. High exposure to saltwater intrusion, with a maximum of 7.8, is also observed in virtually the entire urban area of the Tulum Hotel Zone, both north and south. Puerto Morelos City and the largest city of the State, Cancún, are moderately exposed with 7.1 (Figure 2 and Table 3).

The construction process of the GALDIT index highlights its adaptation to the characteristics of the Yucatan Peninsula aquifer considering what Lobo-Ferreira & Chachadi (2005) described, assigning the lowest exposure score to regions with aquifer thickness values greater than 10 m and the highest to regions with a thickness of less than 5 m. Similarly, as a direct indicator of the concentration of chloride ions in groundwater, EC was considered for the impact parameter of the current SWI (I), as suggested by Chang et al. (2019).

The hydrogeological characteristics of the region also increase the vulnerability of coastal systems exposed to saline intrusion and pollution (Kantun Manzano et al. 2018), especially due to the high hydraulic conductivity and the very low hydraulic gradient that characterize the northern portion of Quintana Roo (Bauer-Gottwein et al. 2011; Gondwe et al. 2011). These conditions make aquifers more susceptible to increases in salinity due to the rising sea level (Ferguson & Gleeson 2012).

Cancún, the largest city in demographic and spatial terms, is in a region with values indicative of moderate susceptibility to salinity. Therefore, it is necessary to continuously assess water management by considering water use and consumption, as improper aquifer management may increase groundwater consumption and salinity. This recommendation is important because it focuses on conserving water for future generations and addresses the needs and objectives of the Regional and National Water Plan (CONAGUA 2021).

The area surrounding the city of Tulum obtained the highest GALDIT indices, especially in front of the coast. Very high, high, and moderate levels stand out on this polygon, whose dimensions are approximately 30 km from north to south and 5–11 km perpendicularly to the coast, with exposure values of 6.7–9.2, respectively. This implies that the hydrogeological conditions combined with anthropic actions could be major factors determining the GALDIT index values observed in this area.

Furthermore, the exposure to saline intrusion of areas that concentrate extraction wells was analyzed considering their spatial distribution and distance from the coast; these areas are key because the water that supplies the entire northern region of the state is obtained from them. The results indicate that the extraction system is vulnerable, as exemplified by the case of Tulum. Although this city is not directly on the coast, the area of influence of wells that supply freshwater to Tulum shows high GALDIT indexes, which may indicate a highly exposed zone in the aquifer to saline intrusion in the Tulum region, similar to those suggested by Supper et al. (2009).

One limitation of this study is the limited density of information at the state level. The databases used only have a suitable data density in the north of the state but not in the central and southern zones. The central area is particularly important since this area, the so-called Mayan Region, is inhabited by a population with high poverty and marginalization levels; however, no data on saline intrusion are available. Therefore, it is worth highlighting that continuous and systematic monitoring of these variables is required to follow the behavior of these areas of interest through time to detect a potential increase in the GALDIT index, which would indicate the existence of saline intrusion.

It should be noted that the GALDIT index only identifies the susceptibility of the aquifer to salinization but does not recognize the causes, anthropic activities, or other related multifactorial analyses. It would be interesting to contrast the results of this index with the rise in the average sea level, variations in recharges, and other meteorological threats. In this way, the different scenarios could be analyzed considering the projections of the effects of climate change. On the other hand, the advantages of the method used are its flexibility and adaptability to the specific needs of the study area.

This work highlights the need to include these elements in water management to serve as technical elements to assess freshwater use and consumption in coastal areas, considering the basic elements of proper management, as mentioned by Foster & Chilton (2018): (a) preserve the current state of groundwater in terms of maintaining water quality and levels within the current ranges; (b) prevent groundwater levels or quality from dropping below a predefined condition set out in the acceptability criteria; and (c) reverse an existing trend of declining groundwater levels or quality to achieve a satisfactory status within a given time frame. This can lead to improved sustainability of water supply, reduced costs, improved accessibility, and aquifer conservation (Wang et al. 2012; Trabelsi et al. 2016). Finally, the current forecasts of an increasing saline intrusion in coastal areas suggest that water will be extracted from more continental and distant sources of supply, increasing the needed infrastructure and, hence, the costs.

The groundwater consumption projections and the effects of climate change for Quintana Roo, in the future point to an unfavorable outlook for water supply systems since the main cities of this region, analyzed here are in areas with moderate and high exposure to saline intrusion into the aquifer on which they depend.

Although there are other alternatives to freshwater supply, such as desalination technology, there are insufficient technical elements to assess the feasibility of their implementation in the study region, and the existing infrastructure is designed to supply a percentage of the population. Desalination is not necessarily a sustainable solution to water scarcity without reducing resource exploitation, living within hydrological and economic boundaries, and ensuring affordable access to water for all (Bell 2018). More sustainable options, such as demand management, water reuse, and rainwater harvesting, can be tools for integrated water management for Quintana Roo. These adaptation strategies should be addressed in detail for each of the coastal cities of Quintana Roo.

Fostering greater public participation and strengthening collaboration among government entities, society, and other key stakeholders is crucial. Furthermore, developing high-frequency monitoring networks to track groundwater levels, water quality, and extraction rates will provide a robust database that could generate highly detailed information for better decision-making at both governmental and community levels. Thus, these actions will contribute to developing future integrated watershed management plans for the specific needs of the population and environment (De Stefano et al. 2011; Akhmouch & Clavreul 2018; Salgado López 2021).

Implementing training and education programs for both authorities and the public, as well as reviewing and strengthening legal and institutional frameworks, are vital steps toward sustainable groundwater management (De Stefano et al. 2011; Villholth & López-Gunn 2018); therefore, promoting water conservation and efficient use through advanced technologies and awareness campaigns, alongside investing in enhancing water infrastructure is essential, considering community participation in decision-making processes will reinforce governance, leading to more inclusive and effective management. Thus, these elements contribute to inclusive water-for-use planning and developing specific adaptation and mitigation strategies for regional and global challenges, such as the effects of climate change on groundwater availability and quality or ensuring water security for future generations and protecting local ecosystems (Akhmouch & Clavreul 2018; Salgado López 2021).

Currently, the hazard approach of saline intrusion is not included in the Vulnerability and Risk Atlases produced by the National Centre for Disaster Prevention (CENAPRED 2024), and hydrological hazards do not consider the hydrogeological particularities of the region. Therefore, the results of this research are highly valuable for their incorporation into these tools, and they should be considered in future instruments of territorial planning and zoning, environmental management, and risk management. These results could be considered an additional component of the State Risk Atlas and the next Regional Water Program in the Hydrological-Administrative Region XII Yucatán Peninsula (CONAGUA 2021). Integrating these results into the generation of risk indices will enable a more precise evaluation and prioritization of adaptive and mitigation actions. These efforts will significantly contribute to the hydric resilience and sustainability of the region regarding the future challenges of the community and the natural environment.

Finally, this research is expected to foster additional analyses that can provide more information about the aquifer, strengthen the knowledge of hydrogeological conditions, and examine different scenarios considering climate change to design preventive actions of consumption reduction, reuse of treated water, or desalination infrastructure, management strategies, plans, or projects aimed at reducing the inherent vulnerability of the region.

The results of the present study identified and classified different areas of the Quintana Roo coast from the perspective of exposure to saline intrusion into groundwater. This information is important to implement actions to prevent or mitigate the effects of saline intrusion on aquifer management.

This research shows that the GALDIT index is a simple and useful tool that can generate information for policymakers and stakeholders on the north coast of Quintana Roo to develop and implement strategies to reduce the vulnerability of natural resources and communities in the region. Nevertheless, one of the limitations of the GALDIT index is its inability to distinguish between different sources of salinization, such as chemical contamination or surface migration, apart from saline intrusion. Despite this limitation, the GALDIT index provides a valuable preliminary assessment, employing hydrogeological parameters to offer a comprehensive evaluation of coastal aquifers.

The research results suggest that significant changes in the approach to groundwater governance should be implemented to address current growing challenges, such as saline intrusion, considering demographic growth and land use planning in Quintana Roo. In addition, the sustainability of groundwater-dependent ecosystems should be fully integrated through economic and non-economic approaches, such as legal, institutional, environmental, cultural, and political challenges.

Future research efforts should focus on improving the GALDIT index by investigating factors such as sea level rise, variations in recharge rates, and other meteorological threats. It will allow for the construction of more comprehensive scenarios that account for the impacts of climate change. By integrating the water management principles outlined in this study – such as maintaining water quality and levels, preventing groundwater degradation, and reversing negative trends – we can improve the sustainability of water supply systems. It, in turn, will help protect aquifers from increasing SWI challenges in Quintana Roo.

In the future, it is suggested that the database be expanded, different methodologies explored for more precise analyses, technologies such as artificial intelligence incorporated for predictive model development, and innovative water management strategies evaluated, considering GALDIT is a good preliminary screening that offers an integrated approach to coastal aquifers using its hydrogeological parameters. In addition, it is critical to continue to study SWI processes and adapt monitoring strategies to address these challenges in the context of evolving climatic conditions. These collective recommendations aim to strengthen research efforts and make meaningful contributions to sustainable water management in Quintana Roo and other coastal regions facing similar issues.

It is imperative to find tangible and viable solutions in such an important and relevant territory that has undergone multiple spatial and social changes in a very short period and to ensure the region's water security for future generations.

The information is available upon request from the National Water Commission. https://sigagis.conagua.gob.mx/gas1/sections/listado.html.

The first author thanks UNAM-DGAPA for the support through the 2022–2024 Postdoctoral Grant at the Institute of Geography. The authors also thank the National Water Commission for its valuable database contributions. Thanks to Dr. Naxhelli Ruiz Rivera for his valuable comments and contributions to the research and María Elena Sanchez for the assistance in the translation.

DGAPA-UNAM Postdoctoral Researchers Grant 2022-2024.

Data cannot be made publicly available; readers should contact the corresponding author for details.

César Alejandro Canul-Macario works at the National Water Commission.