David Serrano, Xander Huggins , Tom Gleeson, Sam Zipper , Florian Jehn, Melissa M. Rohde, Robin Abell, Kari Vigerstol, Andreas Hartmann 

Protected areas are a key tool for conserving biodiversity, sustaining ecosystem services and improving human well-being. Global initiatives that aim to expand and connect protected areas generally focus on controlling ‘above ground’ impacts such as land use, overlooking the potential for human actions in adjacent areas to affect protected areas through groundwater flow. Here, we assess the potential footprint of these impacts by mapping groundwatersheds. We find that over five in six protected areas globally (85%) have groundwatersheds that are underprotected. Half of all protected areas have a groundwatershed with a spatial footprint that lies predominantly (i.e., at least 50%) outside of the protected area’s boundary. These findings highlight a widespread potential risk to protected areas from activities affecting groundwater within their groundwatersheds, underscoring the need for groundwatershed-based protection measures. Delineating groundwatersheds can catalyze needed discussions about protected area connectivity and robustness, and investments in groundwatershed conservation and management can help protect groundwater-dependent ecosystems from external threats.