Environmental Engineering Reference
In-Depth Information
In some cases, the relation between water availability and the actual trade pattern is
even counter-intuitive. North China, for instance, has a very low availability of water per
capita, unlike South China, but nevertheless, there is a very signi
cant trade in food from
North to South China (Ma et al., 2006). Of course, this does intensify the water problems
in the North. A similar case can be found in India, where water has become relatively
scarce in the northern states of Punjab, Uttar Pradesh and Haryana. Nevertheless, these
states export signi
fi
cant volumes of food to the eastern states of Bihar, Jharkhand and
Orissa, which have much larger water endowments than the northern states (Verma et al.,
2008). No simple explanation will su
fi
ce to explain the counter-intuitive situations with
respect to internal trade within China and India, because various factors will play a role,
including historical, political and economic ones. One factor that may play a role as well
is that in water-scarce regions the incentives to increase water productivity are highest. As
a result, it becomes attractive to produce in those regions, which however enhances the
scarcity of the water. This may be a factor in northern India, where water productivities
are indeed much higher than in the eastern states, providing them with a comparative
advantage although the water availability in absolute terms is much lower.
Global water-use efficiency
In the water sector, the term water-use e
ciency is most often used to refer to the inverse
of local water productivity. The latter is expressed as the amount of product made per
unit of water (in the agricultural sector known as 'crop per drop'). Water-use e
ciency is
expressed as the volume of water required to make one unit of product. A water user can
increase local water-use e
ciency by producing the same with less water input. Water
users can be encouraged to do so by charging them a water price that is based on full mar-
ginal cost, by stimulating them to adopt water-saving technology, or by creating aware-
ness that saving water is good for the environment.
The local view on water-use e
ciency is only one way of looking at the subject; there
are two other levels at which one can consider the e
ciency of water use (Hoekstra and
Hung, 2005). At the catchment or river-basin level, water-use e
ciency refers to the
e
ciency at this level can be
enhanced by reallocating water to purposes with higher marginal bene
ciency of water allocation to alternative uses. Water-use e
fi
ts (Rogers et al.,
1998). At the global level, water-use e
ciency can be increased if nations use their com-
parative advantage or disadvantage in producing water-intensive goods to either encour-
age or discourage the use of domestic water resources for producing export commodities.
Much research e
ff
ort has been dedicated to studying water-use e
ciency at the local
and river-basin levels. The research on global water-use e
ciency is of more recent date.
Only four studies have been carried out so far, all of them focusing on the quanti
cation
of physical water savings as a result of global trade, not on the associated economic
savings. All four studies indicate that the current pattern of international trade results in a
substantial global water saving (Oki and Kanae, 2004; De Fraiture et al., 2004; Chapagain
et al., 2006; Yang et al., 2006).
fi
Volume of water saved as a result of international trade
The most comprehensive study on global water saving in relation to international trade was
the one carried out by Chapagain et al. (2006). According to their study, the global water
use for producing agricultural products for export amounted to 1250 billion m
3
/yr (in the
