Abstract: Optimized grain virtual water trade is an effective strategy to alleviate water scarcity in food supply regions through the regulation of trade structures. Through the development of an interval stochastic water resource management model platform coupled with virtual water trade optimization, we examined the effects of virtual water trade optimization on water scarcity and water systems in net virtual water export basins. The results showed that: (1) The marginal water use benefit, pollution load, and water resource endowment of sub-basins were key regulating factors in the virtual water trade optimization process. Sub-basins characterized by low marginal water use benefits, high pollution discharge, and water scarcity tend to be net virtual water importers. (2) Virtual water trade optimization would alter initial water rights allocation, with net virtual water-importing sub-basins showing significant reductions in allocated water rights and net exporting sub-basins exhibiting increased allocations. (3) Water scarcity in net virtual water-exporting basins can be mitigated through the optimization of virtual water trade. Under the optimization mechanism for virtual water trade (OP) during drought years, the total basin water scarcity was reduced by 30.22%-32.66% compared to the conventional virtual water trade mechanism (NP), indicating enhanced drought adaptation capacity in the OP-based water management scheme. Sectorally, the most significant reduction in water scarcity was observed in fisheries, while the smallest reduction occurred in planting. Sectoral water scarcity was jointly affected by water use marginal benefits and cross-section water quality controls. (4) The virtual water trade optimization mechanism enhances basin water supply capacity through coordinated cross-regional allocation based on disparities in sub-basin water resource endowments on one hand, and through reduced water demand for quality maintenance via water quality target management on the other. This was the fundamental mechanism by which water scarcity in net virtual water-exporting basins would be alleviated. (5) The virtual water trade optimization mechanism enhanced the overall basin marginal benefit by 3.59%-3.61% through redirecting water resources from sub-basins with lower marginal benefits to those with higher marginal benefits, and simultaneously expanded water supply capacity, resulting in a system benefit increase of 4.76%-4.77%.

Key words: virtual water trade optimization, net virtual water exporting basin, water quality control system, water shortage, uncertainty