Groundwater resources in the Greater Mekong Region: A review

Study region The Greater Mekong Region, comprising Myanmar, Thailand, Laos, Cambodia, and Vietnam, covering an area of nearly 2 million km 2 . Study focus Groundwater resources have become increasingly crucial to support the region's rapid development. Advancements in hydrogeological knowledge have led to a better understanding of groundwater availability and water quality at both national and sub-national levels. However, very little attention has been given to integrating groundwater knowledge at the regional scale, leading to major data gaps between national studies and global hydrogeological knowledge. This study aims to address these major data and knowledge gaps by conducting a comprehensive hydrogeological review of 179 documents focused on the Greater Mekong Region in Southeast Asia. New hydrogeological insights for the region The review provides the first synthesised overview of the hydrogeology of the Greater Mekong Region. The results are new regional hydrogeological maps of aquifer distribution and groundwater threats from arsenic pollution, high salinity, and over-abstraction. The maps serve as the basis for a unified transboundary framework and an overview of the most significant groundwater challenges. The review also shows that, beyond transboundary aquifers, there are similarities among major aquifer systems and significant differences in the management and development of water resources across borders. Hence, regional cooperation and exchange of lessons learnt in similar hydrogeological settings would be highly beneficial for sustainable groundwater development across the region.