Why Groundwater Use Location Matters in Transboundary Aquifers

Transboundary aquifers extend beneath nearly all international land borders and underlie about 35% of global groundwater-irrigated cropland. Yet only 11% of country pairs sharing an aquifer report an operational cooperative arrangement, and fewer than 5% are covered by a formal treaty. In the era of Global Water Bankruptcy, strengthening this cooperation is an important policy priority. Sharing an aquifer does not necessarily mean sharing the same groundwater problem. Pumping affects groundwater levels most strongly near the well, so intensive use close to a border has greater potential for cross-border effects than comparable use farther away. Drawing on an analysis of 568 country–aquifer pairs, this brief finds that depletion and groundwater-dependent irrigation tend to concentrate near international borders, even though average depletion is no greater than in comparable domestic aquifers. It identifies four groundwater-use configurations: Interior Use, Urban Border, Distributed Agriculture and Border Locked. Each calls for different management options, and expanding irrigation could push more shared aquifers toward greater cross-border interaction. The brief recommends three priorities: identifying where groundwater use could create cross-border impacts, matching cooperation to the potential for cross-border interaction, and preserving spatial separation where feasible.