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Virtual water
is defined as water embedded in commodities (Allan 1998). As a rule
of thumb, a grain crop transpires about 1 cubic meter of water in
order to produce 1 kilogram of grain. Thus importing 1 kilogram
of grain is approximately equivalent to importing 1 cubic meter
of water. Virtual water flows, the flows of water embedded in commodities,
have relevance to water stress, water scarcity, and food security,
as they reduce the need to use water for food production in importing
countries and increase water use in exporting countries. At present,
cereals comprise the majority of the trade in agricultural products,
and therefore tracking trade in cereals is a good indicator of overall
virtual water flows. The map series presented in this section focuses
on cereal trade and virtual water flows to help gain a better picture
of the current global situation with respect to water scarcity and
food security.
The first map
in this series (Map 19a) presents the calorie supply per person
by country for 1995. National-level calorie intake is used as an
indicator of food security. For example, in much of sub-Saharan
Africa (areas in red in map), people do not consume a sufficient
amount of calories, a sign of malnourishment and hence food insecurity.
In countries of food insecurity, countries do not import enough
food to make up the deficit in supplies. Calorie supply per person
is important to understand virtual water flows because population
and dietary requirements drive the need to use water to produce
food.
The second map
in this section (Map 19b) indicates the trade in cereals as a percentage
of total consumption by country. Cereals include wheat, rice, maize,
millet, barley, sorghum, etc. It does not include pulses or tubers.
The map highlights the small number of cereal-exporting countries,
namely Argentina, Australia, Canada, France, Uruguay and the United
States. Other countries produce enough grains for their own consumption,
a condition of self sufficiency, but not a surplus for export. If
maps 19a and 19b are combined, we note that some countries produce
almost enough to match consumption, but that consumption is insufficient
to meet minimum dietary requirements. For example, India has a small
surplus of cereal production (2 percent) but consumes only 2400
calories per day, and Ethiopia has a small deficit of cereal production
(-0.4 percent) and consumes only 1780 calories per day. Within countries,
poor distribution of food can exacerbate food insecurity problems.
Finally, Map
19c indicates the corresponding virtual water flows in terms of
cereal trade. The virtual water flows are estimated as the amount
of crop evapotranspiration equivalent— the amount of water
directly consumed by plants or evaporated in the production process
on irrigated and rainfed land required to produce cereals. While
there are certainly virtual water flows into water stressed countries
of North Africa and the Middle East (see map 15 on average annual
water supply per person), there are also virtual flows into other
countries like Japan or much of sub-Saharan Africa where water scarcity
is not severe, indicating that there are several economic, political,
and food situations beyond scarcity that drive the flows of virtual
water.
Striking on
the map is China. Although more or less self-sufficient in cereal
production (only 4 percent cereal production deficit), China imports
a significant amount of virtual water (16 km3) in cereals. This
is because the population is significant and the consumption level
is high (2766 cal/pc/day). Small changes in China can shift the
global water and food equation. Another interesting case is Japan.
While Japan is not water scarce, the country imports a substantial
amount of its cereal requirements (76 percent of the total consumption)
and hence is a big virtual water importer (25 km3). Most Northern
African and West Asian countries are physically water scarce but
have high daily calorie supplies due to substantial food imports
and hence virtual water flows into these countries are large. Finally,
many countries in sub-Saharan Africa import small amounts of virtual
water, even though malnutrition is prevalent and there is no physical
water scarcity. In these countries the stakes are high for food
and environmental security. Producing more food within these countries
can help food security but this option has high water-related environmental
costs. How far can virtual water flows be used to provide food security?
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