Groundwater, constituting approximately 30% of global freshwater reserves, is a critical resource for domestic, agricultural, industrial, and environmental needs in the Lower Mekong Region. The transboundary Cambodia-Mekong River Delta Aquifer System (CMRDAS), shared by Cambodia and Vietnam, plays a vital role in sustaining regional livelihoods but faces increasing pressures from urbanization, climate change, and weak governance arrangements. Despite its importance, a comprehensive quantitative framework for assessing groundwater governance in transboundary aquifer systems remains lacking. This study addresses this gap by developing a generic, indicator-based framework for assessing transboundary groundwater governance. The framework integrates four governance dimensions, namely Technical, Legal and Financial, Institutional, and Operational, operationalized through 27 indicators and synthesized into a Transboundary Groundwater Governance Index (TGGI) measured on a standardized scale from 0 to 3. The framework was validated through expert-based assessment and subsequently applied to the CMRDAS using a structured survey of groundwater governance stakeholders from the Lower Mekong Region. The results indicate that groundwater governance in the CMRDAS remains at an incipient stage, with a TGGI score of 0.84, reflecting limited progress in transboundary coordination. Significant governance gaps persist across operational, institutional, legal, and financial dimensions, particularly at the transboundary level compared to national contexts. Governance provisions and institutional capacity were consistently more developed in Vietnam than in Cambodia, highlighting asymmetries in governance maturity and implementation capacity. The study identifies key priorities for strengthening groundwater governance, including reallocating financial resources, enhancing institutional capacity, fostering inclusive and participatory policy frameworks, improving transparency and data sharing, and reinforcing local and transboundary coordination mechanisms. Overall, the framework provides a replicable and policy-relevant tool to support the diagnosis and improvement of groundwater governance in transboundary aquifer systems.
