Exploring the trade-offs between agricultural water security and grain production capacity in water source areas: a case study of the Han River Basin, China

Growing food demand intensifies water resource constraints in agricultural regions. The middle and lower reaches of the Han River Basin, serving as both a water source for the South-to-North Water Diversion Project and a major grain-producing region, face complex water-food trade-offs. This study constructs a 17-indicator evaluation system across six dimensions using a four-dimensional framework. Employing four-quadrant, coupling coordination degree, relative development degree, and obstacle degree models, the study analyzes 19 counties' coordinated development from 2010 to 2021. Results show the agricultural water security index increased from 0.204 to 0.233, while food production capacity grew from 0.295 to 0.324. The coupling coordination degree improved from 0.484 to 0.505, remaining in the adjustment stage with slow evolution from near-disorder to barely coordinated. Agricultural water security consistently lagged behind food production capacity. Main obstacle factors were water conservancy construction expenditure (60.80%), agricultural water resources (20.93%), and drought-flood guaranteed area (13.50%). The 19 counties were classified into three regions: core grain production areas, agricultural advantage development areas, and green ecological protection areas. Improving obstacle factors through region-specific strategies represents the main pathway for sustainable development.