Accounting for a scarce resource – virtual water and
water footprint in the global water system
Hong Yang
Swiss Federal Institute for Aquatic Science and Technology (eawag)
[email protected]
Department of Environmental Sciences, Basel University
May 2013
Content
• Why do we need to account for VW and WF?
• The development in methodological approaches
• Scope of the studies and the latest knowledge and
understanding of the relevant issues
• The main limitations, pitfalls and challenges
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1. Why do we need to account for VW and WF
• The world’s available freshwater resources are limited and
unevenly distributed.
• The use and consumption of water resources in one location
can exert impacts on freshwater resources in other locations
through trade.
• This interconnection renders the local water resources and
their management with a global dimension.
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Types of VW and WF
• VW and WF are both defined as the water used/consumed during the
production process.
•
The term WF is usually used in the context where consumers or
producers of products are concerned,
• The term VW is mostly used in the context of international or
interregional trade.
• VW and WF have been categorized into green (soil moisture), blue and
grey (water needed to dilute the polluted water to certain standard).
• Weighted WF typically incorporates water scarcity index or pollution
indicator in the quantification of WF.
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2. Development of VW and WF accounting approaches
Methods
Rule of
the
thumb
Crop
modeling
Aggregation
over space and
supply chain
Bottom up
approaches
Life cycle
assessment
(LCA)
InputOutput
(IO)
Multi-regional
Input-Output
(MRIO)
Top down
approaches
Start from the entire economic
system. Then breakdown to
individual economic sectors. IO
specifies how the water flow among
sectors through supplying inputs for
the outputs (where the virtual water
is embedded) in the economic
system.
Sectors
m3/10,000Yuan
Total Direct water use water use coefficient coefficient
1 Agriculture
924
1181
2 Coal mining and processing
22
140
3 Food and tobacco processing
23
523
4 Textile goods
21
520
5 Clothing
4
306
6 Sawmills and furniture
2
279
7 Paper and products
64
320
8 Petroleum processing
18
144
9 Chemicals
34
239
10 Non‐metal mineral products
16
184
11 Metal smelting and products
29
217
12 Machinery and equipment
3
152
13 Transport equipment
4
147
14 Electric equipment, telecommunication equipment
2
140
15 Other manufacturing
3
165
16 Electricity, gas and water production and supply
575
840
17 Construction
3
159
18 Wholesale and retail trade and passenger transport
28
124
19 Restaurant and hotel
120
441
20 Other services
16
114
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3. Scope of the accounting and the latest knowledge
and understanding of relevant issues
Scope of accounting
Increase
Primary
items
Production
chain
Accuracy of values (data)
Consumer interest
Producer relevance
Economic Catchment
Administrative
/industrial
& river
region(s)
sector
basin
Complexity of the
accounting system
Significance in global
water system
Policy relevance
Increase
Multiple
region(s)
What has been learnt from the latest studies
The application of systematic and sophisticated models has improved
the analysis of interconnections of water uses across economic
sectors, administrative regions and hydrological systems (catchment
and river basin) through the VW trade.
E.g., GIS-based crop modeling, LCA, IO
The effort to incorporating environmental impact into VW and WF
accounting facilitated the assessment of damages or benefits (in
much lesser circumstances) of human appropriation of water
resources in specific locations and their repercussions to other
locations.
E.g., weighted WF incorporating water scarcity index and water
pollution indicators.
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Examples for China
(Unit: 106m3)
Input-output model application. (Zhang et al., 2011)
160000
142634
140000
120000
100000
82641
74457
80000
68177
60000
43602
39038
40000
20000
0
Virtual Wate Export
2002
Virtual Water Import Net Virutal Water Export
2007
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Sectoral breakdown accounting for VW export
2007
3.Food and
tobacco
processing
7%
Other sectors
10%
18.Wholesale
and retail
trade and
passenger
transport 16%
4.Textile
goods 28%
5.Wearing
20%
14.Electric
equipment,
telecommunic
ation
equipment
19%
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4. Main limitations, pitfalls and challenges
1) Data availability and accuracy
Data lacking and lagging
Climate change
Uncertainty
2) Pitfalls - Interpretation of results with intuition
• Mismatch of water endowments and VW trade means
inefficient use of water resources X
• Global water footprint standards and labeling X?
• Consumer action – avoid consuming products from water
scarce regions. X
3) Flaw of the concept of grey water footprint – accounting for
something not there. How to improve it remains a challenge.
4) The direct policy relevance of VW and WF remains limited.
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Thanks for your attention!
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