The puzzling yet tractable diversity of global groundwater sustainability challenges

Global groundwater sustainability is a grand challenge that requires diverse approaches to account for local contexts. Yet, global groundwater assessments often focus solely on aggregate physical trends in storage, levels, and fluxes, overlooking the diversity of social-ecological functions provided by groundwater and their associated sustainability challenges. Here, we introduce groundwater sustainability puzzles as a concept and approach to identify distinct configurations of groundwater challenges within heterogeneous landscapes. Synthesizing 17 global datasets on groundwater functions and management problems, we map more than 200 puzzles worldwide, each representing a specific and spatially defined setting in which sustainability transformations must take root. Notably, half of global land area, population, and crop production situate within 20 or fewer puzzles respectively. This puzzle typology presents the most comprehensive assessment to date of the multi-dimensional composition of global groundwater challenges and offers a tool to facilitate cross-regional learning and network formation across similar contexts.