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| Titel |
Analysis of virtual water flows associated with the trade of maize in the SADC region: importance of scale |
| VerfasserIn |
J. M. Dabrowski, E. Masekoameng, P. J. Ashton |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 13, no. 10 ; Nr. 13, no. 10 (2009-10-23), S.1967-1977 |
| Datensatznummer |
250012031
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| Publikation (Nr.) |
 copernicus.org/hess-13-1967-2009.pdf |
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| Zusammenfassung |
| The concept of virtual water encourages a country to view
agricultural crops in terms of the amount of water required to produce those
crops, with a view to implementing trading policies that promote the saving
of scarce water resources. Recently, increased attention has focussed on
partitioning the virtual water content of crops into green and blue water
(derived from rainfall and irrigation, respectively) as the latter has
higher opportunity costs associated with its use and therefore impacts
directly on scarcity. Maize is the most important crop traded within the
SADC region. South Africa is the largest producer and exporter of maize,
with the majority of its exports destined for other SADC countries. In
comparison to other SADC countries, South Africa produces maize relatively
efficiently, with a low virtual water content and a high green (868 m3 t−1)
to blue (117 m3 t−1) water ratio. The blue water
content is however higher than for maize produced in all other SADC
countries, with the exception of Namibia (211 m3 t−1). Current
trade patterns therefore result in a net expenditure of blue water (66×106 m3),
almost all of which is exported by South Africa (65×106 m3).
South Africa is one of the most water scarce countries in
the region and analysis of virtual water flows indicates that current SADC
maize trading patterns are influenced by national productivity as opposed to
water scarcity. The virtual water content of maize was estimated for each of
South Africa's nineteen Water Management Area's (WMA) and used as a proxy to
represent water use efficiency for maize production. The virtual water
content varied widely across all of the WMAs, ranging from 360 m3 t−1
in the Ustutu Mhlatuze to 1000 m3 t−1 in the
Limpopo. A comparison of the virtual water content and production of maize
(expressed as a percentage of the total national production) identified
those WMAs where maize production is highly water inefficient (e.g. Lower
Orange and Limpopo WMAs). Results suggest that, while a national estimate of
the virtual water content of a crop may indicate a relatively efficient use
of water, an analysis of the virtual water content at smaller scales can
reveal inefficient use of water for the same crop. Therefore, analysis of
the virtual water content of crops and trading of agricultural products at
different spatial scales (i.e. regional, national and WMA) could be an
important consideration within the context of water allocation, water use
efficiency and alleviation of water scarcity. |
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