Water Scarcity Risks in Ammonia Fertilizer Production Pose a Threat to Global Food Security

Ammonia, the foundation of fertilizers, grows food that feed 3.8 billion people. While recent efforts focus on ammonia emissions and costs, water use and scarcity risks remain understudied. We quantify water consumption of ammonia production, evaluate exposure to water scarcity for each of the 406 global plants, and trace how fertilizer trade redistributes water stress across supply chains, estimating how many people rely on food grown with fertilizers produced in water-scarce regions. We find that ∼18% of global ammonia output (∼33 Mt NH₃ yr^-1) experiences at least one month of scarcity annually. The sector's reliance on 406 large, geographically concentrated plants further heightens vulnerability, as local shortages can cascade globally through highly interconnected trade networks. Five exporters (China, Russia, Egypt, Saudi Arabia, and Qatar) account for half of global fertilizer exports, linking the food security of 637 million people to production under water-stressed conditions. Major importers such as Brazil, the U.S., and India are indirectly exposed to water scarcity in distant basins, with the largest trade routes including Qatar-U.S., Qatar-Brazil, and China-Brazil. We show that water scarcity at ammonia production sites represents not merely a local constraint but a systemic risk to global food systems, highlighting the importance of explicitly incorporating water availability into decarbonization strategies and trade policies.