Water footprint (WF) is the volume (expressed in m3) of water used to produce a good or a service, measured at the place where the good was actually produced. The water volume required to produce a good varies in space depending on climatic conditions, soil properties, management choices, and irrigation practises.
In the figure we select the top ten goods, responsible for nearly 60% of the total WF of agricultural production and livestock in year 2011. Each bar represents the total WF of each good and it is evaluated as the sum of all the countries WF, which contribute to the global production.
The WF of a single product in a given country is the product between the total prodcution (tonne) and the water
used per unit of good produced (m3/tonne).
Each product is connected with the country of origin, chosen among the top ten countries by water footprint. The bar length stands for the WF of production measured in each country. It is given by the sum of WFs over all the agriultural and animal products that are produced in the country. For instance, in China over 60% of the total WF is arisen by the production of the top ten products selected.
Water network & trade
The light blue circle represents the WF of production (WP), the orange circle is the WF of consumption (WC), the green circle is the water volume embedded in the import flows of agricultural and animal goods (WI), and the plain yellow circle is the water volume embedded in the export flows of goods (WE). These factors must satisfy the following water balance at the country scale: WP + WI = WC + WE.
In this figure we represent the most important international flows of virtual water, i.e., from the top ten exporters to the top fifteen importers. Each flow is proportional to the water volume embedded in the traded goods. The embedded water is computed as the product between the amount of good exported from the country of origin to the country of consumption and the unit WF of the product in the country of origin (that correspond to the country of production).
In this part we show the impact of importing countries on surface water resources worldwide. The impact is assessed through the evaluation of an environmental cost index defined by the environmental relevance of the impacted fluvial ecosystem and the downstream river network affected by the water withdrawal.
The circle size is proportional to the relative contribution of each importer to the total environmental cost due to the production of the good. For instance, China is responsible for 70% of the total environmental cost generated by soybean production worldwide.