Department of Environment, Land and Infrastructure Engineering, Politecnico di Torino, Torino, Italy.
PLoS One. 2014 Apr 11;9(4):e93084. doi: 10.1371/journal.pone.0093084. eCollection 2014.
The current trade of agricultural goods, with connections involving all continents, entails for global exchanges of "virtual" water, i.e. water used in the production process of alimentary products, but not contained within. Each trade link translates into a corresponding virtual water trade, allowing quantification of import and export fluxes of virtual water. The assessment of the virtual water import for a given nation, compared to the national consumption, could give an approximate idea of the country's reliance on external resources from the food and the water resources point of view. A descriptive approach to the understanding of a nation's degree of dependency from overseas food and water resources is first proposed, and indices of water trade virtuosity, as opposed to inefficiency, are devised. Such indices are based on the concepts of self-sufficiency and relative export, computed systematically on all products from the FAOSTAT database, taking Italy as the first case study. Analysis of time series of the self-sufficiency and relative export can demonstrate effects of market tendencies and influence water-related policies at the international level. The goal of this approach is highlighting incongruent terms in the virtual water balances by the viewpoint of single products. Specific products, which are here referred to as "swap products", are in fact identified as those that lead to inefficiencies in the virtual water balance due to their contemporaneously high import and export. The inefficiencies due to the exchanges of the same products between two nations are calculated in terms of virtual water volumes. Furthermore, the cases of swap products are investigated by computing two further indexes denoting the ratio of virtual water exchanged in the swap and the ratio of the economic values of the swapped products. The analysis of these figures can help examine the reasons behind the swap phenomenon in trade.
当前的农产品贸易，涉及各大洲的各种联系，导致了“虚拟”水（即生产食品过程中使用的、但不包含在食品中的水）在全球范围内的交换。每一个贸易环节都转化为相应的虚拟水贸易，从而可以量化进出口虚拟水的流量。评估一个国家相对于国内消费的虚拟水进口，可以从粮食和水资源的角度大致了解该国对外部资源的依赖程度。本文首先提出了一种从海外粮食和水资源角度理解一个国家依赖程度的描述性方法，并设计了水贸易灵巧性（相对于效率低下）的指数。这些指数基于自给自足和相对出口的概念，系统地计算来自 FAOSTAT 数据库的所有产品的指数，以意大利作为第一个案例研究。对自我维持和相对出口的时间序列的分析，可以展示市场趋势的影响，并影响国际层面的水相关政策。这种方法的目标是通过单一产品的视角突出虚拟水平衡中的不一致条款。实际上，特定的产品（这里称为“交换产品”）被确定为由于其同时高进口和出口而导致虚拟水平衡效率低下的产品。由于两国之间相同产品的交换而导致的效率低下，是以虚拟水的数量来计算的。此外，还通过计算两个进一步的指数来研究交换产品的案例，这两个指数分别表示交换的虚拟水量和交换产品的经济价值之比。分析这些数字可以帮助检查贸易中交换现象的背后原因。
