A great number of transboundary water systems of the world, including transboundary aquifers (TBAs), support the socioeconomic development and wellbeing of an important part of the world’s population. At present, nearly 600 TBAs have been defined in the Americas, Africa, Asia, and Europe. Transboundary water issues abound and are complicated by lack of adequate governance and shared management. Of upmost importance to resolve those issues are the background assessments, legally-binding agreements and by the fact that in many cases institutional asymmetries do not allow for a standardised knowledge.
We present a critical look at the transboundary aquifer issues, based on the analysis of identified TBAs, and discuss what is working and what it is not to illustrate the most important steps and lessons learned, as well as the good practices needed for water management in the transboundary context.
Our analysis of the current state of knowledge of TBAs in four continents shows that information on most transboundary aquifers remains limited. Given important aspects related to incomplete or contradictory knowledge on TBAs, the large number of stakeholders and opinions involved, scarce legal agreements, and the interconnected nature of these problems with other problems, take us to conclude that groundwater science alone cannot solve transboundary groundwater issues.
In Africa, cooperation on aquifer management has improved, even in the absence of legally-binding agreements. In Asia, TBAs identification, assessment and shared management is still limited. In the Americas, important lessons were learned from the collaborative assessment of some TBAs shared by Mexico and the USA, as well as the Guarani in South America. In Europe, the extension and size of TBAs are generally limited compared to aquifer systems in other parts of the world, the geological complexity in the region and fragmented information, has led to some inconsistencies of methodological approaches to map TBAs.
Issues that still need to be addressed are: hydrogeological understanding of the transboundary systems, clear and unambiguous delineation of TBAs, indicators of cooperation, data harmonization and information sharing and management, and water use conflicts or impacts of global changes in the systems. Addressing these issues requires a concerted effort of all stakeholders involved to establish a satisfactory balance between scientific knowledge and efficient management and protection of transboundary waters.