Hidden Hurdles in Agricultural Water Scarcity Assessments: A Case Study in China

Precise agricultural water scarcity assessment is the precondition for advancing agricultural water management under climate change. It reflects the deficit between agricultural water demand () and supply potential (), primarily in the irrigation sector. However, neither nor can be directly observed at large scales, and current assessments rely on model‐derived estimates whose accuracy cannot be validated. These unverified estimates remain the only means by which scientists assess water scarcity. Here we propose a novel observational approach to qualify the difference between and by monitoring how real irrigation water withdrawal responds to climate‐induced variability in water demand and supply. Using China as a case study, we demonstrate remarkable uncertainties in Global Hydrological Model estimates, including inverse prediction of inter‐annual irrigation withdrawal fluctuations in many provinces. Contrary to previous studies, our findings reveal that water stress seems more prevalent in southern China than in northern China during the study period. Earlier studies may underestimate in northern China by overlooking non‐renewable water sources such as groundwater and glacier melt. While in southern China, may be systematically overestimated by ignoring the strong limitations imposed by storage, conveyance, and irrigation infrastructure. This is the first time that the imbalance between and has been evaluated from an observation perspective, revealing overlooked scarcity in water‐rich regions and challenging long‐held perceptions of China's water stress patterns. We anticipate that our approach will serve as an new path for validating water scarcity assessments. It can also be an auxiliary tool to identify missing factors in Global Hydrological Models, improving the accuracy of future projections for agricultural water management.