3. Indeed, direct international imports correspond to 20% of the total VWT volume in 2005, and are re-exported to multiple provinces throughout the country (SI Appendix, Fig. Agriculture is located mainly in the dry north, where irrigation largely relies on groundwater reserves. It comprises six income groups per region, with farm supply represented at the level of 2,433 administrative units (virtually all counties), and accommodates for every county outputs of 28 products and 14 land use types in cropping and livestock production. This paper analyzes the role of international and interprovincial food trade in China’s national agricultural water-use and food supply. Image credit: NASA’s Goddard Space Flight Center. We use simulations of 2005 trade flows, a year for which the model has been calibrated with available data. Thus, it seems that a reorganization of corn production and trade, or an improvement in water-use efficiency targeted at corn in Inner Mongolia, would be important in reducing national water use. The VWC of unprocessed livestock products is defined as water consumption per head of livestock (kilograms of water per head)—involving feed’s VWC and drinking and cleaning water—divided by the livestock production per head (kilograms of meat per head) (see details in SI Appendix). 4B). VWC ranges from about 700 kgwater/kgcrop for crops produced in Tibet to more than 2,300 kgwater/kgcrop in Hainan province, and from about 2,000 kgwater/kgmeat for meat produced in Guangdong to nearly 5,500 kgwater/kgmeat in Inner Mongolia (Fig. The VWT flows corresponding to direct international imports and to domestic trade of foreign commodities are obtained by multiplying the trade volumes by the VWC of the corresponding commodity in the ROW. We use the global hydrological model H08 (16, 17) to estimate crop water use at 0.5° spatial resolution before aggregating to the province level. Importantly, when incorporating foreign imports, China’s soy trade switches from an inefficient system to a particularly efficient one for saving water resources (20 km3/y irrigation water savings, 41 km3/y total). This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Specific provinces also might be targets for improvements of water-use efficiency: provinces that export large quantities of crops while relying significantly on irrigation, such as Inner Mongolia—which is the largest corn exporter and uses a great deal of irrigation—and the northeastern provinces (e.g., Heilongjiang for rice and Hebei for pork). Astronomers ostensibly know plenty about neutron stars. It thus accounts for crop water consumption. 18; Materials and Methods and SI Appendix). We build the VWT (kilograms of water) network by multiplying the traded volume of a specific commodity (kilograms of product) by the VWC of this commodity (kilograms of water per kilograms of product) in the province of export. The VWC value of each commodity was calculated by using provincial crop yield estimates from CHINAGRO (15) (for rainfed and irrigated lands) and ET simulated with the H08 global hydrological model (16, 17). Our findings support the urgency to implement water-saving means in agriculture, which might involve trade mechanisms. H.Q. The tendency seems to allow miniaturized organisms to pack enough cells into a tiny form to build a complex physiology. To be able to track the re-export of foreign goods within Chinese borders, we have distinguished foreign and domestic commodities in our optimization procedure (Materials and Methods and SI Appendix). Most of these studies have been carried out at the large regional scale (i.e., eight administrative divisions). (iv) Which province or commodity might be targeted to reduce water use without decreasing current national food production levels? We apply a linear programming optimization procedure (20) to downscale the interregional trade matrices to interprovincial trade matrices by minimizing the total cost of trade for each commodity (see details in SI Appendix). 2; notice the different scale for soy and pork). We still identify important exporting provinces, such as Shaanxi, Shandong, and Henan (including trade of foreign goods or not) and major importers, such as Shaanxi, Guangdong, and Guangxi. Finally, international trade flows through the four harbors (in Shanghai, Tianjin, Liaoning, and Guangdong) is imposed exogenously, based on reported data (21). Note the spatial variability and the general dominance of livestock VWC (which accounts for feed provenience) vs. crop VWC. 4A). Top exporting provinces are colored with the same scheme as in Fig. 3). (19) found that although many Chinese cornfields have reached the yield ceiling, some large areas remain nutrient limited, and a few are limited by both nutrient and water. Moreover, the northeastern provinces of China grow a large part of their crops for nondirect human uses, such as animal feed and biofuels. (iii) What is the role of foreign trade in China’s VWT network and in the associated water savings? The water used throughout the production process of a good is referred to as “virtual water.” In the case of products containing virtual water (i.e., requiring water for their production), trade is a means of transferring water resources between regions. However, Foley et al. 4B). Moreover, the share of blue and green water sources in total VWC also varies among provinces (Figs. Online ISSN 1091-6490. Besides, possible reorganization of crop trade is limited by factors other than water, such as cropland availability and food self-sufficiency policies. 4A). In particular, soy always requires much more water than the other three main crops: rice, corn, and wheat (SI Appendix and Fig. This is also the case in a few regions of the world: the midwestern United States, northwestern Europe, and some parts of Brazil and Argentina. performed research; C.D., N.H., and H.Q. We compute the global water savings for all trade relationships and aggregate WS values by the commodity’s base product (corn, rice, soy, wheat, ruminant, pork, and poultry) as follows:WSx=∑(i,j)WSi,j,x,[3]. The global water savings through trade of a local commodity x from an exporting province i to an importing province j are defined (6) asWSi,j,x=Ti,j,xloc⋅(VWCj,x−VWCi,x),[1], and water savings from the trade of a foreign commodity from province i to j, because x actually is made abroad (in the ROW), are defined asWSi,j,x=(Ti,j,xfor−∑k≠i,jTj,k,xfor)⋅(VWCj,x−VWCROW,x),[2]. Author contributions: C.D., D.L.M., and I.R.-I. Water is one of China's most critical natural resources since it is used for different purposes such as generating electricity and irrigating farms. acknowledges the support of the National Natural Science Foundation of China (71222302, 71073154) and the support of the Newton Fellowship, United Kingdom. In addition, we observe differences in VWC among crops within the same province. Agriculture still concentrates most of the national water withdrawal. contributed new reagents/analytic tools; C.D. Recently, this threat to water availability and quality triggered grand water projects, such as very large dams and canals [e.g., South–North Water Transfer, which has the opposite direction as most VWT flows, but does not compensate them (12)].
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