History and Results of <scp>U.S.</scp> /Mexico Groundwater Data Exchange Programs in the Paso del Norte Region, 1897 to 2022

The transboundary Hueco Bolson aquifer is the primary water supply for El Paso, Texas, and Ciudad Juárez, Mexico as well as U.S. Army Fort Bliss and smaller cities in Texas and Mexico. Binational groundwater data exchanges between the United States and Mexico that have focused on the aquifer have evolved over more than a century, shaped by scientific, political, and social dynamics. The history can be viewed through distinct periods. Efforts to understand the groundwater resource began with early reconnaissance surveys and have evolved through successive efforts to refine the characterization of groundwater flowpaths, residence times, surface water-groundwater interactions, and aquifer salinization. Lessons from these efforts highlight the importance of perseverance, mutual respect, and formal agreements, such as the 1999 memorandum between El Paso Water Utilities and the Junta Municipal de Agua y Saneamiento de Juárez, in sustaining long-term cooperation. The accumulated datasets chronicle the evolution of hydrogeologic conceptual and mathematical models while providing a foundation for ongoing research, sustainable water-use strategies, and the long-term stewardship of the Hueco Bolson aquifer shared by El Paso and Ciudad Juárez. The Hueco Bolson case demonstrates how long-term, cooperative data collection can improve scientific understanding and management of complex transboundary aquifer systems.