Tag Archives: virtual water

Mapping global flows of virtual green and blue water

Green and blue virtual-water ‘flows’ related to wheat trade by major exporting and importing nations (km3/year). The size of each pie is determined by the amount of virtual water ‘traded’. Countries with virtual-water ‘exports’ are depicted in green and countries with virtual-water ‘import’ in red;<br /> the colour shade depends on the quantity of virtual water ‘traded’. Period 2000–2004.
Green and blue virtual-water ‘flows’ related to wheat trade by major exporting and importing nations (km3/year).
The size of each pie is determined by the amount of virtual water ‘traded’.
Countries with virtual-water ‘exports’ are depicted in green and countries with virtual-water ‘import’ in red; the colour shade depends on the quantity of virtual water ‘traded’. Period 2000–2004.

M.M. Aldaya, J.A. Allan and A.Y. Hoekstra in their paper Strategic importance of green water in international crop trade (Ecological Economics 2009) doi:10.1016/j.ecolecon.2009.11.001 map global flows of virtual water in the wheat trade.

In their paper they explain their figure:

The map presented in Fig. 6 shows the virtual-water ‘flows’ to the five major importing countries for wheat for the period 2000–2004.

By ‘importing’ virtual water embodied in agricultural commodities, a nation “saves” the amount of water it would have required to produce those commodities domestically.

Though from an importing country perspective it is not relevant whether products have been produced using green or blue water in the country of origin, from a global point of view it has important implications (Chapagain et al., 2006a). For instance, Egypt is the largest importer of wheat, with the USA providing about 45% of the country’s imports. Wheat from Egypt has an average virtual-water content of 930 m3/ton of which 100% is blue water (Chapagain et al., 2006a), while the USA has a virtual-water content for wheat of 1707 m3/ton of which 39.8% is blue water (Table 3).

By importing wheat, Egypt saves 930 m3 of water per ton of wheat. Globally, when imported from the USA, there is not a total water saving because wheat production in the USA requires more water than in Egypt. Exports to Egypt from this country result in a considerable net global water loss of 777 m3 per ton. However, if we just look at blue water only, importing wheat from the USA to Egypt saves 251 m3/ton (since USA production requires 679 m3/ton of blue water and wheat production in Egypt 930 m3/ton).

Along these lines, Egypt, as some other water-scarce importing countries, has formulated policies to import low value but high water consuming food like cereals (Van Hofwegen, 2005). Nevertheless, even if the potential of trade to “save” water at national level is substantial, most international food trade occurs for reasons not related to water resources (CAWMA, 2007).

Maping global virtual waters flows

Fig. 4. World map of virtual water exports. (a) Total virtual water exports (flows exceeding 10 km3 yr−1 are shown); (b) flows of virtual water exports originating from blue (irrigation) water (flows exceeding 1.0 km3 yr−1 are shown); and (c) virtual water exports originating from nonrenewable and nonlocal blue water (flows exceeding 0.5 km3 yr−1 are shown).
Fig. 4. World map of virtual water exports.
(a) Total virtual water exports (flows exceeding 10 km3 yr−1 are shown);
(b) flows of virtual water exports originating from blue (irrigation) water (flows exceeding 1.0 km3 yr−1 are shown); and
(c) virtual water exports originating from nonrenewable and nonlocal blue water (flows exceeding 0.5 km3 yr−1 are shown).

Figure is from Hanasaki and others paper An estimation of global virtual water flow and sources of water withdrawal for major crops and livestock products using a global hydrological model (2009 Journal of Hydrology) doi:10.1016/j.jhydrol.2009.09.028.

They explain the figure:

The estimated flows of virtual water exports and imports in 2000 by nation were aggregated into 22 regions worldwide (Table 9; Fig. 4) to show net exports between regions.

Fig. 4a shows the virtual water export flows for all water sources. The figure indicates that North and South America were major regions from which virtual water export flows originate; East Asia, Europe, Central America, and West Asia were the major destinations. This pattern of flows agrees with the studies of (Oki and Kanae, 2004), (Yang et al., 2006) and (Hoekstra and Hung, 2005).

Fig. 4b shows the virtual water exports of blue water (withdrawn from streamflow, medium-size reservoirs, and NNBW sources), and

Fig. 4c shows the virtual water exports of NNBW. Most major flows of blue water and NNBW originated from North America and South Asia.

Interestingly, South America was the major total virtual water exporter but a minor blue water exporter because less cropland is irrigated on this continent.

Notably, South Asia, which is densely populated and where demand results in water scarcity (Oki and Kanae, 2006 and Hanasaki et al., 2008b), showed blue and NNBW virtual water export flows. [note: NNBW - is non-renewable and non-local blue water.]