Current Status and Future Directions in Modeling a transboundary aquifer: a case study of Hueco Bolson

The Hueco Bolson aquifer is a binational aquifer shared by the United States of America (USA) and Mexico that is strongly interconnected with the transboundary river, Rio Grande/Rio Bravo. Increasing urbanization and intensified agriculture along with climate change have resulted in overdrafting groundwater resources and stressed the aquifer, threatening the aquifer life if mitigation actions are not taken soon. In the past, the aquifer's hydraulic gradients and flow directions have changed due to the high groundwater withdrawal rates from the two major cities El Paso (USA) and Ciudad Juarez (Mexico). This study presents a comprehensive overview of Hueco Bolson aquifer modeling history and makes a case for future modeling and engagement. First, we discuss the evolution of groundwater modeling from the past to the present. Second, we explore advances in coupling surface and groundwater physically-based modeling to simulate interactions of groundwater and surface water. The coupled numerical models were used to understand the water budget for both aquifer and the river. Third, we present water management issues, including water quality and quantity, equity, stakeholders participation, and climate change. We propose graphical quantitative modeling (e.g., System Dynamics model and Bayesian belief network models) as necessary to include experts' opinions and enhance stakeholder's participation in all aspects of modeling. Finally, we highlight the need for a transboundary data-sharing platform, updated water data (quality and quantity), and improvement of the current model. Though the insights are based on a case study, the approaches we discussed in this study provide the necessary strategies to overcome the challenges involved in a transboundary aquifer.