Analysis of water-carbon spatiotemporal linkages and potential carbon neutrality benefits in China at the regional-industrial composite scale based on virtual water trade

The interregional grain trade system fosters a complex water‑carbon coupled network, which exacerbates spatial disparities in both water allocation and carbon transfer. Previous studies focused on the virtual water trade's role in food security and agricultural water use but overlooked inter-industry “water–carbon” transfer mechanisms. This study pioneers two innovative metrics: Virtual water flow spillover efficiency and potential carbon neutrality benefit, thereby expanding the analytical perspective to unravel the interregional water‑carbon flow mechanisms within regions. This study constructs a spatiotemporal analytical framework for China's grain-related virtual water‑carbon flows at a regional-industrial nexus scale by integrating social equity principles with an optimized minimum cost maximum flow algorithm. And establishes a synergistic optimization methodology for “regional carbon reduction - water use efficiency enhancement”, enabling precise identification of dual optimization pathways for resource-environment systems. Results reveal that China's virtual water flow for rice, wheat, and corn increased by 18.2 %, and virtual carbon flow increased by 18.3 % totally. The northeast emerged as a major virtual water exporter, while coastal provinces shifted toward net import status, exacerbating regional water disparities. This study illuminates the substantial carbon benefits arising from intra-industrial resource restructuring triggered by regional grain trade. These benefits far surpass previous estimates derived solely from interregional carbon emission reductions, thereby challenging the conventional accounting framework for its systemic underestimation of grain trade's carbon mitigation potential. Critical pathways, notably Hebei-Tianjin and Shanxi-Guangdong, were identified as dual resource-environment optima. These pathways facilitate water‑carbon constructive collaboration within large-scale agricultural trade systems, thereby providing actionable strategies for sustainable food-water‑carbon nexus management.