Transboundary Aquifers of the World map 2021

Transboundary Aquifers of the World map 2021

TBA Map 2021

Groundwater is the most abundant source of freshwater on earth, accounting for approximately 97% of non-frozen fresh water. It is an important natural resource that greatly contributes to human development. Approximately 50% of the world’s population drinks groundwater daily. It is often critical for sustaining rural populations that are located away from surface water and piped infrastructure. With respect to food production, groundwater is estimated to contribute to over 40 percent of the world’s production of irrigated crops. Groundwater sustains ecosystems, maintains base flow of rivers and stabilizes land in areas with easily compressed soils. Aquifers can also buffer impacts resulting from seasonal variability and climate change. However, groundwater does not stop flowing at political borders and huge resources are stored in transboundary aquifers. Therefore, the identification, mapping, assessment and development of governance mechanisms for transboundary aquifers (TBAs) are important tasks for ensuring the sustainability of these resources and peaceful cooperation between countries. 40% of the worlds available water is transboundary. The assessment of global groundwater resources is one of the core activities of the International Groundwater Resources Assessment Centre (IGRAC). Next to the assessment, IGRAC – as UNESCO/WMO groundwater centre – facilitates and promotes global sharing of information and knowledge. In both activities, transboundary aquifers take a prominent place.

There are now 468 identified transboundary aquifers and aquifer systems identified, underlying almost every nation, increased from 366 in 2015. The United Nations International Law Commission’s Draft Articles on the Law of Transboundary Aquifers (Draft Articles) define an aquifer as “a permeable water-bearing geological formation underlain by a less permeable layer and the water contained in the saturated zone of the formation.” The Draft Articles further define a transboundary aquifer or a transboundary aquifer system as “an aquifer or aquifer system, parts of which are situated in different States. The number of transboundary aquifers has been increasing steadily since the first ‘Transboundary Aquifers of the World Map; was released in 2009. It is likely that new transboundary aquifers will still be identified in the future and that the delineation of existing transboundary aquifers may be refined once further studies are conducted.

For more information on individual transboundary aquifers and the extended view of the small aquifers, please visit IGRAC’s Global Groundwater Information System (GGIS) online:

Preferred citation

IGRAC (International Groundwater Resources Assessment Centre), 2021. Transboundary Aquifers of the World [map]. Edition 2021. Scale 1 : 50 000 000. Delft, Netherlands: IGRAC, 2021.