Coupled water–carbon burden transfers in staple-crop supply chains: trade-driven responsibility shifts, inequality signals and sustainability options in China

Freshwater scarcity and decarbonization targets jointly constrain staple-crop provisioning, yet water footprint (WF) and greenhouse-gas (GHG) burdens are often evaluated separately, obscuring coupled pressures and trade-mediated responsibility shifts. We developed an integrated water-carbon sustainability accounting framework for China's five staple crops (wheat, rice, maize, soybean, and potato) using a 2020 baseline. Spatially explicit production, blue/green/gray WF, province-crop GHG intensities, edible-portion calorie denominators, and interprovincial trade flows were linked to estimate irrigated and rainfed burdens under mass- and calorie-based functional units. WF and GHG intensities were generally positively coupled but varied across crops and production systems, reflecting shared irrigation-energy and nitrogen-related pathways. Interprovincial trade reallocated 362.7 Gm 3 of WF and shifted coupled burdens from exporting to importing provinces; consumption-based attribution attenuated co-burden inequality (G-WSI: −0.124 to −0.033; edible-corrected G-GHGIcal: +0.291 to +0.175), but did not remove upstream burden concentration. Edible-corrected calorie-scale coupling was significant for rice (R 2 = 0.407, p < 0.001), soybean (R 2 = 0.304, p < 0.001), and maize (R 2 = 0.112, p = 0.043), but weaker for wheat and potato. Inequality signals remained sensitive to accounting perspective, ordering criterion, functional-unit choice, and spatial aggregation, with regional summaries masking substantial provincial heterogeneity. The findings support equity-aware, scale-sensitive interventions that combine irrigation efficiency, low-carbon pumping, improved nutrient management, methane mitigation, scarcity-informed sourcing, and responsibility-sharing mechanisms across staple supply chains.