Geography of groundwater use and depletion in internationally shared aquifers

Transboundary aquifers (TBAs) underlie 35% of global groundwater-irrigated cropland, yet few are covered by formal cooperative arrangements. Whether this limited cooperation is consequential depends in part on where groundwater is used within shared aquifers, because pumping far from international borders may generate little cross-border impact. Combining ∼ 116,000 well observations with global irrigation data across all 426 known TBAs, we assess how groundwater use and depletion differ from comparable domestic systems and how they are distributed relative to international borders. While we find no evidence of greater average depletion in TBAs, depletion is more strongly concentrated toward international borders in shared aquifers and varies substantially across systems. Irrigation is also more intensive and concentrated toward borders in shared aquifers, although much of this pattern is attenuated after accounting for border rivers. Groundwater-supplied irrigation remains more border-proximate after accounting for these rivers. A dyad-level typology distinguishes shared systems according to where groundwater demand is concentrated, linking their potential for cross-border interaction to different management options. These findings suggest that transboundary groundwater governance should be organized around the geography of groundwater use and potential cross-border interactions rather than treating shared aquifers as uniform governance units.