Water Resources and Industry 1–2 (2013) 49–59
Contents lists available at ScienceDirect
Water Resources and Industry
journal homepage: www.elsevier.com/locate/wri
An assessment of the virtual water balance for
agricultural products in EU river basins$
D. Vanham n
European Commission, Joint Research Centre (JRC), Institute for Environment and Sustainability (IES), Ispra, Italy
a r t i c l e in f o
Keywords:
Water footprint
Virtual water
EU
Europe
River basin
Trade
a b s t r a c t
In this paper the virtual water balance for agricultural products in river
basins located in the EU28 (European Union and Croatia) is assessed.
Only basins with a surface area larger than 1000 km2 are analysed.
More specifically the net virtual water import of agricultural products
(nVWi, agr) in these basins is assessed. The latter is defined as the
difference between the water footprint of consumption (WFcons, agr)
and the water footprint of production (WFprod, agr) for agricultural
products. Overall the EU28 is a net VW importer for agricultural
products, i.e. it imports more VW than it exports. However, there are
large differences between different EU regions. River basins which are
identified with high positive nVWi, agr values (net VW importer basins)
include the densely populated and industrialised regions of western
Europe like the Rhine, Elbe, Po, Seine, Scheldt or Thames basins. On the
other hand high negative nVWi, agr values (net VW exporter basins) are
observed for rural and sparsely populated river basins on the Iberian
Peninsula (Guadiana, Ebro, Duero), in western France (Loire, Garonne)
and the eastern Baltic region (Nemunas).
& 2013 The Authors. Published by Elsevier B.V. All rights reserved.
1. Introduction
The virtual water (VW) and water footprint (WF) concepts [2,9] have been brought into water
management science in order to show the importance of consumption patterns as well as global
dimensions in good water governance [16,8]. Regarding the WF a distinction needs to be made
between the WF of production (WFprod) and the WF of consumption (WFcons). The WFprod is the sum of
☆
This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No
Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the
original author and source are credited.
n
Tel.: þ 39 332783951.
E-mail addresses: [email protected], [email protected]
2212-3717/$ - see front matter & 2013 The Authors. Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.wri.2013.03.002
50
D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
the direct and indirect water use of domestic freshwater resources of a geographical region. The
WFcons is defined as the total volume of freshwater that is used to produce the goods consumed by the
inhabitants of a geographical region. It is the sum of direct and indirect water use of domestic and
foreign water resources through domestic consumption.
A review on the WF concept for the EU28 (the current European Union and Croatia) is given in
Vanham and Bidoglio [16]. It is shown that: (1) the EU28 is a net virtual water importer; (2) 60% of the
WFcons is internal and 40% external to the EU28 and (3) the WF of agricultural products contributes by
far the largest fraction of the total WFprod (91%) and WFcons (89%). Therefore substantial WF reduction
potential exists in both water efficiency in agricultural production processes (WFprod) and
consumption behaviour adaptations of EU citizens (WFcons) [15,17].
There are large spatial differences in WFprod and WFcons amounts throughout the EU28. As a result
both net VW import and export regions exist within the EU28. Net VW import/export amounts have
been quantified on the national level worldwide [11]. Integrated water resources management needs
to be assessed at the river basin or catchment scale. Therefore the aim of this paper is to quantify the
net VW import and export amounts for agricultural products (which account for about 90% of total WF
values [16]) for the river basins of the EU28.
Up to date WF and VW analyses on the river basin level have not been the focus of much research.
Some case studies include the Guadania [1] and Duero [5] river basins on the Iberian Peninsula or the
Heihe [21] and Haihe [22] river basins in China. Blue monthly water scarcity based on the blue WFprod
for 405 global river basins was assessed by Hoekstra et al. [12].
2. Methodology
The VW balance for agricultural products is defined as [10]
net VW i, agr ¼ VW i, agr −VW e, agr ¼ WF cons, agr −WF prod, agr
ð1Þ
with net VWi, agr being the net VW import related to the net import of agricultural products; VWi, agr
the VW import related to the import of agricultural products; VWe, agr the VW export related to the
export of agricultural products; WFcons, agr the WFcons related to the consumption of agricultural
products and WFprod, agr the WFprod related to the production of agricultural products.
In order to assess the net VWi, agr for the river basins of the EU, national values on WFprod, agr and
WFcons, agr are extrapolated to livestock and population raster data and subsequently aggregated to the
river basin level. All WF values are composed of a green, blue and grey component and were taken
from Mekonnen and Hoekstra [14].
An overview of used data is given in Table 1. The analysis concerns average annual values for the
period 1996–2005. The catchment database for continental Europe (CCM2) developed by Vogt et al.
[18] (based on the digital elevation model SRTM—Shuttle Radar Topography Mission–of 90 m
resolution) was used to identify the river basins (Fig. 1). Selected basins have to fulfil two conditions:
(1) they are fully or partly located in the EU28 and remaining Balkan countries and (2) they have a
surface area larger than 1000 km2.
Table 1
Specification of data used in the analysis.
Data
Catchment database for continental Europe (CCM2)
Population, raster 1 1 km2
WFprod agricultural crops, raster 5′ 5′ (or 0.0833n 0.08331)
Gridded livestock of the world (GLW), raster 1 1 km2
(cattle, buffaloes, goats, sheep, pigs and poultry)
National stock data on horses, asses and mules
National WFprod data for livestock (grazing and service water)
National WFcons data for agricultural products
Period
Data source
2000
1996–2005
2000
Vogt et al. [18]
CIESIN [4]
Mekonnen and Hoekstra [14]
FAO [6]
1996–2005
1996–2005
1996–2005
FAOSTAT [7]
Hoekstra and Mekonnen [11,14]
Hoekstra and Mekonnen [11,14]
D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
51
Fig. 1. River basins larger than 1000 km2, located (partly) in the EU28 and remaining Balkan countries.
A workflow of the methodology is presented in Fig. 2. The total WFprod, agr is composed of a WFprod,
of crops and a WFprod, agr of livestock. A WFprod of agricultural crops raster, with a global extent, is
available within the WaterStat database on the water footprint network (WFN) website [19]. The data
are presented in [14]. This raster was used for the case study area. It also comprises the crops which
are used as feed. To assess a WFprod, agr of livestock raster, national WFprod, agr data for grazing and
livestock service water [14] were extrapolated by means of the gridded livestock of the world (GLW)
rasters for different livestock types [6]. The group horses, asses and mules is not represented by a GLW
raster. To spatially distribute this livestock type, national stock data [7] are interpolated by means of
the cattle GLW raster.
The WFcons for agricultural products is spatially distributed by means of national WFcons, agr values
from Mekonnen and Hoekstra [14] and the population raster of CIESIN [4].
agr
3. Results and discussion
3.1. General
Fig. 3 shows the WFprod for agricultural products (WFprod, agr) for crops (taken from Mekonnen and
Hoekstra [14]) and for livestock, as extrapolated by means of the GLW raster datasets and national
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D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
Fig. 2. Workflow of the methodology.
WFprod, agr data for grazing and livestock service water. For the total EU28 the WFprod, agr for crops
amounts to 491 km3 and for livestock 61 km3 (total WFprod, agr is 552 km3) [16].
Fig. 4 shows the WFcons for agricultural products (WFcons, agr), as the result of national per capita
WFcons, agr data extrapolated with CIESIN [4] population raster data. A zone of high concentrated
WFcons, agr amounts can be observed along the so-called “Blue Banana” area of Europe [3,13], a bananashaped metropolitan axis running from North West England in the North to Milan in the South.
Absolute VW balance values (net VWi, agr) for EU river basins are shown in Fig. 5. Positive values
indicate that the WFcons, agr is larger than the WFprod, agr. The main explanations to the latter are the
facts that: (1) for particular products the river basin is not self-sufficient and/or (2) the production of
agricultural goods is very water productive (lower virtual water content or VWC) as compared to
other river basins from which goods are imported. Negative values indicate a WFcons, agr which is
smaller than the WFprod, agr. The same explanations hold: (1) for particular products there is more
produced than consumed in the river basin and/or (2) the production of agricultural goods is not as
water productive (higher VWC) in the river basin as compared to in other river basins from which
goods are imported. Water productivity here refers to the product units produced per unit of water
consumption or pollution [10]. The value of the VWC is a measure for water productivity, and is
dependent on production methods (yield, method of irrigation, etc.), but also natural conditions
(climate and soil). Therefore it can differ substantially for different regions, even for neighbouring
farmers. This means that also within the EU28 important differences exist. Wheat, e.g. has a lower
VWC in western Europe (e.g. DE 788 m3/ton) and northern Europe (e.g. UK 607 m3/ton) as compared
to southern Europe (e.g. ES 1476 m3/ton) or eastern Europe (e.g. RO 1779 m3/ton) [16].
River basins with the highest positive net VWi, agr are located along the Blue Banana region: the
Rhine (41189 Mm3), Po (18335 Mm3), Thames (1203 Mm3), Scheldt (9674 Mm3), Elbe (8226 Mm3) and
Seine (7981 Mm3). Following are the Tajo (7791 Mm3), Danube (6746 Mm3), Meuse (6260 Mm3) and
Rhone (5782 Mm3) river basins. River basins with the highest negative net VWi, agr (or positive net
VWe, agr), are located on the Iberian Peninsula (Guadiana −9120 Mm3, Ebro −8088 Mm3, Duero
−7876 Mm3, Guadalquivir −5869 Mm3), in Western France (Loire −6990 Mm3, Garonne −5006 Mm3)
and the eastern Baltic Region (Nemunas −6210 Mm3, Dniester −4515 Mm3).
D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
53
Fig. 3. WFprod for agricultural products (WFprod, agr, in Mm3), for (a) crops (raster 5′ 5′ or 0.08331 0.08331) and (b) livestock
(raster 1 1 km2).
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D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
Fig. 4. WFcons for agricultural products (WFcons,
agr)
in Mm3 (raster 1 1 km2).
When the absolute net VWi, agr values of Fig. 5 are related to the area of the river basins (Fig. 6),
generally the same observations can be made. However, the highest positive and negative values are
now in relatively small basins like the Besòs river basin (3.04 Mm3/km2)-in which a large part of the
city of Barcelona is located-or the Carapelle river basin in Southern Italy (−0.25 Mm3/km2). Of the
river basins with high positive net VWi, agr per km2 values, the larger basins include the Thames
(0.89 Mm3/km2), Scheldt (0.51 Mm3/km2), Rhine (0.26 Mm3/km2) and Po (0.26 Mm3/km2). Of the
river basins with high negative net VWi, agr per km2 values, the larger basins include the Guadiana
(−0.14 Mm3/km2), Somme (−0.13 Mm3/km2), Guadalquivir (−0.10 Mm3/km2), Ebro (−0.09 Mm3/km2)
and Garonne (−0.09 Mm3/km2).
Fig. 7 shows for the river basins the relationship between the population density (in people per
km2) and the net VWi, agr per km2 of the river basin. The net VWi, agr per km2 increases with increasing
population density (coefficient of determination R2 ¼0.70 concerning all assessed river basins).
Negative net VWi, agr per km2 values only occur for low population densities (lower than 208 people
per km2). However, when river basins are selected according to the geographical UN zone they are
located in, some zones show stronger relationships (Southern Europe R2 ¼0.90, Western Europe
R2 ¼0.88 and Northern Europe R2 ¼0.80) than others (Eastern Europe R2 ¼ 0.27 and mixed zone
R2 ¼0.29). In Vanham and Bidoglio [16] it was already pointed out that the characteristics on WFprod
and WFcons are similar amongst the countries of the different EU28 zones. Per capita WFcons values e.g.
D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
Fig. 5. VW balance for agricultural products (net VWi,
agr ¼VWi, agr−VWe, agr ¼WFcons, agr−WFprod, agr)
55
in Mm3.
are generally the highest in Southern Europe and the lowest in Northern Europe. The ratio of the
external WFcons to the total WFcons is in the upper range in Western Europe while the lowest values are
observed in Eastern Europe. The two main factors explaining this divergence are: the difference in
virtual water content (VWC) of produced agricultural goods (generally lower in the northern and
western EU zone as compared to the southern and eastern zone) and the difference in amount and
type of agricultural products consumed.
3.2. Limitations and further research
Due to data availability restrictions, the results of this assessment are not absolute and must be
regarded as best estimates based upon direct underlying data on production (for the WFprod) and
consumption (for the WFcons). The values for both are assessed with the bottom-up approach based
upon FAOSTAT data [7]. Both can be calculated by means of the top–down or bottom-up approach
[11,16]. The bottom-up approach is based upon direct underlying data on production and consumption
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D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
Fig. 6. VW balance for agricultural products per surface area: net VWi,
agr
(in Mm3) per km2.
and is less sensitive to trade data than the top–down approach [11]. As described in Vanham and
Bidoglio [16], the balance WFprod þVWi ¼WFcons þVWe within the geographic WF accounting scheme
as calculated for the EU with the bottom-up approach does not hold 100%. For the EU28 these values
are 609 km3 (WFprod), 421 km3 (VWi), 857 km3 (WFcons) and 115 km3 (VWe) [16]. The balance therefore
shifts between 972 and 1030 km3 (range of about 5%). Theoretically this balance should close.
However, this is not the case due to practical complexities with data (availability of and
inconsistencies in the underlying databases). Regarding only agricultural products, EU28 values are
552 km3 (WFprod), 360 km3 (VWi), 759 km3 (WFcons) and 95 km3 (VWe) [17]. This balance shifts
between 855 and 912 km3 (range of about 6%). Taking this into account, the resulting river basin net
VWi, agr values need to be regarded as best estimates.
Also the methodology used (Fig. 2) results in uncertainties for river basin net VWi, agr values. The WFprod,
agr for crops is originally a raster dataset. The WFprod, agr raster for livestock is however obtained by spatially
disaggregating national data by means of a livestock raster dataset (GLW, Table 1). The WFcons, agr raster is
D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
57
Fig. 7. Graph showing the relationship between the population density of the river basin (in people per km2) with the net VWi,
3
2
agr (in Mm ) per km of the river basin. The river basins are divided according to the geographical zone they are located in
(defined by the UN standard country or area codes and geographical regions): Eastern, Northern, Southern and Western Europe,
as well as a mixed zone for basins which are located in different zones.
obtained by spatially disaggregating national data by means of a population raster dataset (Table 1). This
assumes that the consumption pattern and livestock production conditions are homogenous across all the
river basins in each European country. This is in reality not the case and thus a simplification. To account for
this heterogeneity, regional statistics within a country or country-specific statistics (e.g. urban vs. rural)
could be used. Such more detailed analyses are the subject of further research.
The river basin net VWi, agr assessment presents total values. It does not give information on the
different components (green, blue and grey) of these values. This limits its potential for policy options.
To define policy options, a WF sustainability assessment is required. WFprod, agr values (green, blue,
grey and total) need to be evaluated with respect to local water availability. Net VWi, agr need to be
linked with such sustainability assessments and WFcons, agr amounts. This is discussed in detail in
Vanham and Bidoglio [16]. Also Witmer and Cleij [20] indicate that the local context is essential for
making the WF approach useful for sustainability policies. WF components need to be placed in their
physical and socioeconomic context. Nevertheless, the analyses presented in this paper can at this
stage contribute significantly to raising awareness about the global scale of water appropriation.
Indeed, it shows that apart from local river basin actors, stakeholders and authorities, also distant
consumers, producers and investors along the supply chain can contribute to sustainable water
management in a river basin. The paper e.g. shows the dependency of city dwellers like Barcelona on
water resources from other river basins for their WFcons. The WF and VW concepts give an additional
dimension to IWRM on the river basin scale. This paper presents first net VWi, agr estimations for river
basins larger than 1000 km2 in the EU. With further research the detail of these analyses can be
elaborated and linked to WF sustainability assessments.
4. Conclusions
In this paper the net VW import amounts for agricultural products (net VWi, agr) for the river basins of
the EU28 larger than 1000 km2 (Fig. 1) are quantified. Regarding absolute net VWi, agr values (Fig. 5),
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D. Vanham / Water Resources and Industry 1–2 (2013) 49–59
the highest positive amounts are located along the densely populated and industrialised bananashaped metropolitan axis running from North West England to Milan. In decreasing order these are
the Rhine, Po, Thames, Scheldt, Elbe and Seine river basins. The WFcons, agr is for these basins thus
substantially higher than the WFprod, agr. River basins with the highest negative net VWi, agr, are located
on the Iberian Peninsula (Guadiana, Ebro and Duero), in Western France (Loire and Garonne) and the
eastern Baltic Region (Nemunas). These net exporting river basins are sparsely populated and have
extensive agricultural areas.
Generally the same observations are made when the net VWi, agr is related to the surface area of the
basin (Fig. 6). There is a positive increasing relationship between the latter values and the population
density of the river basins (Fig. 7). A strong correlation is observed in Southern Europe (R2 ¼0.90),
Western Europe (R2 ¼0.88) and Northern Europe (R2 ¼ 0.80).
The paper concludes with the evaluation of the uncertainty of the resulting net VWi, agr values and
the description of potential implications for IWRM. Further research is required.
Disclaimer
The conclusions and statements presented are those of the author and may not in any circumstances
be regarded as stating an official position of the European Commission.
Conflict of Interest
None
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