Aquifers and the groundwater they supply are estimated to provide about “40% of worldwide drinking water needs,” according to a new report by Dr. Rosario Sanchez and colleagues at the Texas Water Resource Institute at Texas A&M University. Aquifers that span international borders play a major role in providing water to often vulnerable populations because they are sometimes the sole supply of this vital resource. The report, titled “Effective transboundary aquifer areas between Mexico and the United States: A border-wide approach,” builds on earlier work by Sanchez and others by seeking to further develop the methodologies necessary to identify and characterize these aquifers.
The management of transboundary aquifers, also known as “hydrogeological units” or “HGUs” is inherently difficult, especially since a complete map of the HGUs along the U.S.-Mexico border did not exist until Sanchez and her colleague Laura Rodriguez published one in 2022. They identified a total of 28 transboundary aquifers and employed an “Effective Transboundary Aquifer Area (ETAA) approach … to delineate those ‘hot spots’ where pumping zones are concentrated.”
In their new report, the authors explain that in addition to the current framework of identifying priority areas along the border, they utilized “well density data, which is a quantifiable approach and provides comparable capabilities among ETAAs.” The refined approach also incorporates “depth contours” to provide greater insights into “groundwater flows and consequently potential impacts at transboundary scale.” According to the report, “There is a correlation between higher density of wells and shallow depths and … the intensity of density across ETAAs varies as well.” This enables a more granular analysis “at regional and local scales in terms of vulnerability to overexploitation and potential contamination of aquifers, which eventually can have an impact on border communities that depend heavily on groundwater to fulfill their social and economic needs.”
These vulnerabilities are being further exacerbated by the depletion of surface water resources shared between Mexico and the U.S. “The Rio Colorado and Rio Grande transboundary basins are experiencing the lowest international reservoir levels of the last one hundred years.” With population-growth and water-demand projections edging ever upwards, the U.S.-Mexico border region could find itself “at the mercy of … poorly regulated and mismanaged available transboundary groundwater resources,” according to the authors.
The report’s “concept of vulnerability pertains to how much the region could be affected by significant or major ETAAs (above 99 wells per 100 km2) combined with its level of groundwater dependency.” In attempting to “identify those regions across the U.S. border that represent the most vulnerable zones in terms of groundwater development and dependency,” the authors found that “New Mexico and Chihuahua show the most dense and vulnerable ETAAs across the border region.” Meanwhile, “Texas and Mexico show the most consistent distribution of lower-density ETAAs covering around 60%” of the 40 aquifers they share.
As with any research, the significance of the findings is informed by the underlying data. “Water use information was available for most of the wells located in the U.S.,” according to the report, “but limited information was available for wells in Mexico.” Sanchez told Our Water Matters that “groundwater monitoring is a recurrent and persistent issue in Mexico [where] … groundwater is regulated by the federal government.” Mexico’s National Water Commission, known as Conagua, “simply does not have the technical, physical, scientific … infrastructure nor the funding” to meaningfully monitor all the groundwater in the country. “Funding has been cut up to 50% over the last 8 years … and that does not seem to be changing anytime soon.” Data collection efforts on the U.S. side of the border are not without their own limitations, however. In Texas, for example, state monitoring efforts might involve measuring water levels in a handful of wells once or twice a year in areas without a groundwater conservation district. Even if an area has a groundwater conservation district, funding constraints often make it difficult or impossible for districts to independently monitor groundwater levels.
Another challenge is the relative invisibility of the groundwater resources we share with Mexico. For example, Texas’ most recent State Water Plan makes no mention of transboundary aquifers. At the federal level, a “Report to the President” published last December during the final days of the Biden administration titled “Improving Groundwater Security in the United States” pays zero attention to this glaring vulnerability. Regardless of the challenges, the report uses the available data to crystallize the task ahead: “Under current water scarcity conditions as well as limited data and resources to assess transboundary aquifers in the U.S.-Mexico border region, an approach that concentrates on identifying specific and local regions at potential risk according to its level of vulnerability and groundwater dependability, is not only necessary but could offer an efficient way to start designing the route for assessing shared groundwater conditions at a border-wide scale with a local focus.”
For Sanchez, “[t]he new approach” is not only “more scientifically robust,” it can also be applied to groundwater anywhere because “all aquifers cross some kind of political jurisdiction” at the local, state, and even regional level, making them “transboundary in some way.” In Sanchez’s view, “water is always shared … What happens upstream affects [people] downstream.” The same is true with groundwater. Just because we do not see it, does not mean” we are not affected. “Whatever happens on one side, will eventually have an impact on the other side.”
Visit www.sciencedirect.com/science/article/pii/S2214581824003525 to read the full report.
Trey Gerfers serves as general manager of the Presidio County Underground Water Conservation District. A San Antonio native, he has lived in Marfa since 2013 and can be reached at tgerfers@pcuwcd.org.