A spatial mismatch in water and arable land availability results in large virtual water transfers through interprovincial food trade in China. Accurately identifying and measuring water-saving links in interprovincial food trade can help to relieve water resources pressure in main grain-producing areas. We use a multiregional input-output table combined with the CROPWAT model to build China's interprovincial virtual water transfer network embedded in food trade in 2012. Then, water saving and scarce water saving are measured. Both consider the difference in water productivity among provinces, but the latter also pays attention to the scarcity of water resources. Finally, we adopt a water footprint to recalculate the scarce water savings without precipitation (green water). Our results indicate that the amount of virtual water transfer embedded in food trade is 74.9 billion m³, which is equivalent to 12.22% of the total water use in 2012. We observe large variations in the relationship between water resources abundance and agricultural water-use efficiency across provinces. Especially, there is a virtual water transfer from provinces with high water productivity but a lack of water to provinces with low water productivity but an abundance of water. The scarce water saving can identify sustainable food trade links, which can alleviate water scarcity in consuming provinces without exacerbating water shortage in producing provinces. In addition, interprovincial food trade results in 15 billion m³ of scarce gray water saving, which is equivalent to 59.76% of the scarce blue water saving. Scarce water saving based on blue water and gray water provides a basis for establishing an interprovincial compensation mechanism to balance the cost of water redistribution caused by food trade.

Iran’s focus on food self-sufficiency has led to an emphasis on increasing water volumes available for irrigation with little attention to water use efficiency, and no attention at all to the role of consumption and trade. To better understand the development of water consumption in relation to food production, consumption, and trade, we carried out the first comprehensive water footprint assessment (WFA) for Iran, for the period 1980–2010, and estimated the water saving per province associated with interprovincial and international crop trade. Based on the AquaCrop model, we estimated the green and blue water footprint (WF) related to both the production and consumption of 26 crops, per year and on a daily basis, for 30 provinces of Iran. We find that, in the period 1980–2010, crop production increased by 175%, the total WF of crop production by 122%, and the blue WF by 20%. The national population grew by 92%, and the crop consumption per capita by 20%, resulting in a 130% increase in total food consumption and a 110% increase in the total WF of national crop consumption. In 2010, 26% of the total water consumption in the semi-arid region served the production of crops for export to other regions within Iran (mainly cereals) or abroad (mainly fruits and nuts). Iran’s interprovincial virtual water trade grew by a factor of 1.6, which was mainly due to increased interprovincial trade in cereals, nuts, and fruits. Current Iranian food and water policy could be enriched by reducing the WFs of crop production to certain benchmark levels per crop and climatic region and aligning cropping patterns to spatial differences in water availability and productivities, and by paying due attention to the increasing food consumption per capita in Iran.

In the past several decades, the irrigation of high-intensity cropping systems has caused serious groundwater depletion in the Beijing–Tianjin–Hebei region. Optimizing the planting structure is a key method for mitigating groundwater decline. However, the optimal planting structure has not been confirmed, and the effect of planting structures has not been quantified in groundwater overdraft areas. In this study, based on a model for planting structure optimization and the elitist nondominated sorting genetic algorithm, the water saving potential was estimated, and the trade-off between water resources and agricultural production was quantified. The results showed the following: (1) The current planting structure is a highly water-consuming system. The winter wheat–summer maize double-cropping system and vegetable and fruit cropping systems are the dominant contributors to crop water consumption, accounting for 90% of the total water deficit. (2) Constrained by regional water resources, it is difficult to achieve the objectives of halting groundwater decline and food self-sufficiency simultaneously unless at least 1.0 billion m³ yr⁻¹ water from the mid-route of the South-to-North Water Transfer (SNWT) project is used for agriculture or wheat imports account for more than 25% (2.84 million ton yr⁻¹) of the regional wheat demand. (3) It is almost impossible to achieve a balance between groundwater exploitation and replenishment only by optimizing the planting structure without decreasing the agricultural output or without using external water. When the planting structure is optimized, to coordinate grain crops, cash crops and water use, at least 81–96% (4.6–5.5 billion m³ yr⁻¹) of the planned water from the SNWT project will need to be used for agriculture. (4) A viable option for restructuring planting should consider the regional self-sufficiency for wheat, a moderate surplus of vegetables/fruits to boost farmers’ income, and appropriate water transfer for groundwater sustainability. The results provide a compromise between food and water in severe groundwater overdraft areas and serve as a quantitative reference for making decisions regarding agricultural and water resource policies.

The winter wheat–summer maize double cropping system caused overexploitation of groundwater in the North China Plain; it is unsustainable and threatens food security and the overall wellbeing of humankind in the region. Finding water-saving cropping systems without compromising food security is a more likely solution. In this study, six alternative cropping systems’ water conservation and food supply capacity were compared simultaneously. A combined water footprint method was applied to analyze the cropping systems’ water consumption. The winter wheat–summer maize system had the largest water consumption (16,585 m³/ha on average), followed by the potato/spring maize, spinach–spring maize, rye–spring maize, vetch–spring maize, pea/spring maize, soybean||spring maize and mono-spring maize cropping systems. For the groundwater, the spinach–spring maize, pea/spring maize, soybean||spring maize systems showed a higher degree of synchronization between crop growth period and rainfall, which could reduce use of groundwater by 36.8%, 54.4% and 57.6%, respectively. For food supply capacity, the values for spinach–spring maize, pea/spring maize, soybean||spring maize systems were 73.0%, 60.8% and 48.4% of winter wheat–summer maize, respectively, but they showed a better feeding efficiency than the winter wheat–summer maize system. On the whole, spinach–spring maize may be a good option to prevent further decline in groundwater level and to ensure food security in a sustainable way.