Surface manifestations of regional groundwater flow systems in the Lower Colorado River Basin. Environmental understanding and management opportunities for a transboundary basin.

The transboundary water resources of the Lower Colorado River Basin necessitate robust and collaborative governance frameworks to address pressing challenges associated with drought conditions and escalating water demands in both the United States and Mexico. Recent Minutes (319, 323, and 330) under the 1944 Water Treaty between the United States and Mexico highlight the critical challenges related to water allocation from the Colorado River, exacerbated by prolonged droughts that have significantly impacted the Upper Basin in recent years. However, few of these Minutes integrate surface water and groundwater management as a core strategy for achieving sustainable resource use, despite the increasing strategic importance of groundwater as a vital supply source for various user groups and economic sectors. This study employs Gravity-Driven Groundwater Flow Systems Theory to analyze publicly available geospatial and environmental data, offering an indirect characterization of regional groundwater flow components. The approach leverages natural features and groundwater data to identify surface manifestations of regional groundwater systems, including recharge and discharge dynamics. The results include cartographic evidence that underscores the critical systemic interrelationship between groundwater and the natural environment, particularly in the context of anthropogenic impacts such as groundwater abstraction and land-use changes. Through environmental interpretation of hydrogeological indicators—including groundwater depth in wells, perennial surface water features, topographic relief, vegetation patterns, and soil characteristics—this study identifies regional recharge and discharge zones shared by Mexico and the United States. These zones illustrate the interconnected nature of transboundary groundwater and its reliance on cross-border collaboration for sustainable management. However, significant data gaps persist between the two nations, particularly in the standardization of methodologies for data collection, interpretation, and spatial coverage. The absence of a consistent and comprehensive framework for studying regional groundwater flows shared across the border underscores the need for enhanced binational coordination. This research emphasizes the necessity of integrating hydrological data and harmonizing policies to ensure equitable and sustainable water resource management in the Lower Colorado River Basin. Addressing these challenges through cooperative mechanisms will be critical for mitigating the impacts of superficial water scarcity and securing the long-term sustainability of shared transboundary water resources.