Development of a unified 3D hydrogeological conceptual model of the Mexicali Valley arid aquifer in north-western Mexico

In this study, a unified 3D conceptual hydrogeological model of the Mexicali Valley aquifer was developed, located in an arid, transboundary region under significant water stress. The aquifer has a complex hydrostratigraphy shaped by varied depositional environments and active tectonics, resulting in high hydraulic heterogeneity. An imbalance between groundwater extraction and recharge has caused a sustained decline in piezometric levels and expanded drawdown cones from 2011 to 2021. Natural recharge is limited, mainly originating from agricultural return flows and seepage from unlined canals, which also contribute to salinization. Isotopic analyses reveal the presence of fossil water and a strong evaporative influence on water quality. The conceptual model integrates hydrogeological, structural, and geochemical data, offering a comprehensive representation of the system. It serves as a valuable tool for sustainable groundwater management and supports decision-making within a binational governance context, addressing the challenges of shared water resources in arid regions.