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Virtual Water Trade from IndiaBY: Vikram Yogi | Category: Agriculture | Submitted: 2017-04-16 06:00:42
Article Summary: "Water is one of the most important inputs to agricultural production. Water is embodied in all products to a greater or lesser degree, but the amount used in production generally exceeds the embodied water. The supply of water to agriculture could be from natural sources, rain or through irrigation. The total amount of water fro.."
Virtual Water Trade from India
Author: Vikram Yogi
The concept of virtual water emerged in the early 1990s and was first defined by Professor Allan (1993) as the water embedded in commodities. Producing goods and services requires water; the water used to produce agricultural or industrial products is called the virtual water of the product. This water is ‘virtual’ because it is not anymore contained in the product. For example "When you consume one kilo of grain, you are in effect also consuming the one thousand liters of water needed to grow that grain similarly when you consume one kilo of beef, you are consuming the 13,000 liters of water needed to produce that amount of meat, and this is the hidden or 'virtual water’.
The potential of the concept:
Water saving: Net import of virtual water in a water-scarce nation can relieve the pressure on the nation’s own water resources. Virtual water trade between nations and even continents could be used as an instrument: to improve global water use efficiency and to achieve water security in water poor regions of the world. Virtual water trade can be an instrument in solving geopolitical problems and even to prevent wars. From an economic point of view it makes sense to produce the demanded water-intensive products in those places where water is most abundantly available .
Virtual water storage:
Virtual water can also play a role in bridging drought periods. Food storage is an effective way of storing water in virtual form and it can be seen as an alternative to real water storage. The food can be generated when water productivity is high and delivered when productivity is low from this we can save significant amount of water.
Virtual water transfer:
Virtual water trade between or within nations can be seen as an alternative option to inter-basin water transfers, especially when land is not a limiting factor for food production. This is for instance very relevant for China and India, where major real water transfer schemes are being considered.
Water footprint: a relevant indicator of water use:
Virtual water is an essential tool in calculating the real water use of a country, or its water footprint. The total water use within a country is not the right measure of a nation’s actual appropriate of the global water resources.
Water foot print of a country = Total domestic water use + Virtual Water import – Virtual water export
The water footprint of a nation is related to dietary habits of people. High consumption of meat gives a large water footprint. Also the more food originates from irrigated land, the larger is the water footprint. Finally, nations in warm climate zones have relatively high water consumption for their domestic food production resulting in a larger water footprint.
Method of calculation:
Virtual water can be expressed as the volume of water used by the exporter to produce the traded amount of food or as the volume of water the importer would have used otherwise. The difference between the two is the net impact of trade on global water use. A further distinction is possible between crop and irrigation water depletion. Depletion is defined as a use or removal of water from a basin that renders it unavailable for further use. Crop water depletion includes crop evapotranspiration and losses because of reservoir evaporation, percolation to saline aquifers and pollution.
Crop Water Depletion:
Virtual water flows can be expressed as the volume of water depletion incurred by the exporting country (equation 1) and as the amount that the importing country would have required otherwise (equation 2):
ETexij = Xij.CWj --------------------- (1)
ETimij = Xij.CWj --------------------- (2)
ETexij = crop water depletion used by the exporting country (m3)
ETimij = crop water depletion the imported would have used (m3)
Xij = net cereal trade from exporter i to importer j (kg)
CW = crop water depletion per unit crop (m3/kg)
i = Exporting country
j = Importing country
The volume of crop water depletion per unit crop is a function of climate (evapotranspiration) and crop yield (determined by, among others, farm inputs, soil characteristics and management, on-farm water). Expressed in cubic meter water per kilogram, it indicates how much water is needed to produce one unit of food. It is estimated from (equation 3):
CW = Amount of water = 10.DP crop -------------------- (3)
Amount of crop Y crop
DPcrop = crop water depletion (mm)
Ycrop = crop yield (kg/ha)
The factor 10 is included to match units: 1 mm on one hectare corresponds with 10 m3 of water. DPcrop includes crop evapotranspiration coming from precipitation and irrigation water. It is computed from:
DP crop = Peff + NET / EE ---------------- (4)
Peff = effective precipitation (mm)
NET = net irrigation requirements (mm)
EE = effective efficiency (%)
NET = ETcrop — Peff --------------------- (5)
ETcrop= kc .ETo ---------------------------- (6)
kc = crop factor
ETo = reference evapotranspiration (mm)
Effective efficiency of irrigation water, defined as the depletion beneficially used by crops divided by total depletion, shows how efficiently irrigation water is managed. The crop factor kc and methods to estimate ETo can be found in FAO Irrigation and Drainage paper no.56. Equations (4) and (5) implicitly assume that, under irrigated conditions, all irrigation requirements are met. This assumption, needed because reliable estimates on deficit irrigation are lacking, may lead to an overestimation of irrigation water savings, especially in water scarce areas where deficit irrigation is common. In rain-fed areas, NET is zero and crop evapotranspiration is met exclusively by effective precipitation.
Irrigation Water Depletion
Analog to the crop water computations, irrigation water depletion can be expressed as the amount that the exporter used and the importer would have used:
IRexij = Xij.IWj ------------------- (7)
IRimij = Xij.IWj ------------------- (8)
IRexij = irrigation water depletion used by the exporting country (m3)
IRimij = irrigation water depletion the imported would have used (m3)
IW = irrigation water depletion per unit crop (m3/kg)
IW= 10.NET / EE ---------------- (9)
The factor 10 is needed to match units from mm per hectare to m3
Impact of Trade on Global Water Use:
The impact of trade on the global crop water use is quantified as the difference of crop water depletion in the exporting country and the crop water “saved” in the importing country:
ETdifij = ETimij —ETexij =X ij.(CWj —CWi) -------------- (10)
ETdifij = difference in crop water depletion between importer and exporter because of trade (m3)
The impact of cereal imports on global water use into country j is given summing all bilateral flows:
TotIRdifj =ΣiIRdifij --------------------- (11)
At global level the impact is:
GlobETdif = ΣiΣjETdifij --------- (12)
A positive value of ETdif signifies that water “savings” because of trade occur as the exporter is more water efficient than the importing country. A negative value suggests that global crop water
depletion increases because of trade since the exporter uses more water than the importer would have. Similarly, the impact of international cereal imports on irrigation water depletion is quantified by:
IRdifij = IRimij — IRexij = X ij.(IWj —IWi) ----------------- (13)
at national level:
TotETdifij = ΣiETdifij -------------- (14)
and at global level
GlobIRDIFij = ΣiΣjIRdif ij ---------------------- (15)
Virtual water content of the livestock product is calculated in two steps
1. Aggarwal, P. K., Talukdar, K. K. and Mall, R. K. (1998), Potential Yields of Rice-Wheat System in the Indo-Gangetic Plains of India. Rice-Wheat Consortium Paper Series 10. New Delhi, India: Rice-Wheat Consortium for the Indo-Gangetic Plains, PP:16.
2. Allan, J. A. (1997), Virtual Water: A Long Term Solution for Water Short Middle Eastern Economies? Paper presented at the British Association Festival of Science, Roger Stevens Lecture Theatre, University of Leeds, Water and Development Session.
3. Chapagain, A. K. and Hoekstra, A. Y. (2003), Virtual Water Trade: A Quantification of Virtual Water Flows in Relation to the International Trade of Agricultural Products, www.siwi.org/waterweek/workshop.
4. Carr JA, D'Odorico P, Laio F, Ridolfi L (2013), Recent History and Geography of Virtual Water Trade. PLoS ONE 8(2): e55825. doi:10.1371/journal.pone.0055825
5. De Fraiture, C., Cai, X., Amarasinghe, U., Rosegrant, M. and Molden, D. (2004), Does International Cereal Trade Save Water? The Impact of Virtual Water Trade on Global Water Use. Comprehensive Assessment Research Report 4. Colombo, Sri Lanka: Comprehensive Assessment Secretariat.
6. Hoekstra, A. Y. and Hung, P. Q., (2003), Virtual Water Trade: A Quantification of Virtual Water Flows between Nations in Relation to International Crop Trade. Value of Water Research Report Series No. 11. Delft, the Netherlands: IHE.
About Author / Additional Info:
I am currently pursuing Ph.D in Agricultural economics from IARI New Delhi.
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