Strategic Importance of Green Water in International Crop Trade
Total Page：16
File Type：pdf, Size：1020Kb
Ecological Economics 69 (2010) 887–894 Contents lists available at ScienceDirect Ecological Economics journal homepage: www.elsevier.com/locate/ecolecon Analysis Strategic importance of green water in international crop trade M.M. Aldaya a,⁎, J.A. Allan b, A.Y. Hoekstra a a Department of Water Engineering and Management, University of Twente, Enschede, The Netherlands b London Water Research Group, King's College & SOAS, University of London, UK article info abstract Article history: Virtual water is the volume of water used to produce a commodity or service. Hitherto, most virtual water Received 28 March 2008 ‘trade’ studies have focused on its potential contribution to saving water, especially in water short regions. Received in revised form 6 November 2009 Very little, however, has been said about the opportunity cost of the associated water. The present research Accepted 7 November 2009 critically evaluates the strategic importance of green water (soil water originating from rainfall) in relation to Available online 26 November 2009 international commodity trade. Besides having a lower opportunity cost, the use of green water for the production of crops has generally less negative environmental externalities than the use of blue water Keywords: Virtual water (irrigation with water abstracted from ground or surface water systems). Although it is widely known that Green water major grain exporters – the USA, Canada, France, Australia and Argentina – produce grain in highly productive Maize rain-fed conditions, green water volumes in exports have rarely been estimated. The present study corroborates Soybean that green water is by far the largest share of virtual water in maize, soybean and wheat exports from its main Wheat exporting countries (USA, Canada, Australia and Argentina) during the period 2000–2004. Insofar virtual water is Trade ‘traded’ towards water-scarce nations that heavily depend on their blue water resources, green virtual-water Blue water use ‘trade’ related to these commodities plays a role in ensuring water and water-dependent food security and avoiding further potential damage to the water environments in both importing and exporting countries. This potential of international green virtual-water ‘trade’, however, is constrained by factors such as technology, the potential for further increases in the productivity of soil and irrigation water, the level of socio-economic development, national food policies and international trade agreements. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Yang et al., 2006). But apart from stressing its potential contribution to water savings, it is also important to establish whether the water used There is a growing body of literature focusing on the concept of proceeds from rainwater evaporated during the production process virtual water and on its potential contribution to saving water, espe- (green water) or surface water and/or groundwater evaporated as a cially in water-short nations (Hoekstra and Hung, 2002; Hoekstra, result of the production of the product (blue water). Traditionally, 2003; Hoekstra and Chapagain, 2008). Few of them, however, focus on emphasis has been given to the concept of blue water through the the relevance of green water (soil water originating from rain) in “miracle” of irrigation systems. However, an increasing number of international commodity trade (De Fraiture et al., 2004; Allan, 2006; authors highlight the importance of green water on ensuring water Chapagain et al., 2006b; CAWMA, 2007). The present research criti- and water-dependent food security through sustaining rain-fed crop cally evaluates the strategic importance and implications of green production (Falkenmark and Rockström, 2004; CAWMA, 2007; Rock- water in international commodity trade. ström et al., 2007). Green water generally has a lower opportunity The virtual-water content of a product (a commodity, good or cost than blue water (Hoekstra et al., 2001; Albersen et al., 2003). service) refers to the volume of water used in its production (Allan, Even if it is more and more upheld that green water represents the 1997, 1999). Building on this concept, virtual-water ‘trade’ represents largest share of virtual water in the international trade of agricultural the amount of water embedded in products traded internationally. commodities, with exports going from green water rich countries International trade can save water globally if a water-intensive towards generally blue water based economies, hitherto, green water commodity is traded from an area where it is produced with high volumes have rarely been estimated. water productivity (ton/m3) to an area with lower water productivity The present research, framed within a more extensive study (De Fraiture et al., 2004; Oki and Kanae, 2004; Chapagain et al., 2006a; (Aldaya et al., 2008), focuses on the current importance of green water within international agricultural commodity trade. This re- search builds on earlier studies, which roughly estimated the share of ⁎ Corresponding author. Tel.: +31 53 489 44 64; fax: +31 53 489 53 77. green water in global agricultural production (Rockström et al., 1999; E-mail address: [email protected] (M.M. Aldaya). Chapagain and Hoekstra, 2004; De Fraiture et al., 2004). Chapagain 0921-8009/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolecon.2009.11.001 888 M.M. Aldaya et al. / Ecological Economics 69 (2010) 887–894 et al. (2006b) carried out detailed calculations of the green water have been equally weighed assuming that the stations represent volumes for cotton production. More recently, Chapagain and Orr equally sized crop-producing areas. The actual irrigation water use (2009) showed the importance of green water in the production of (FAO, 2007a) is taken equal to the irrigation requirements as tomatoes in Spain. The present work complements these studies estimated with the CROPWAT model for those countries where the estimating the green and blue virtual-water content of maize, soybean whole harvesting area is reportedly irrigated. In the countries where and wheat exports from the USA, Canada, Argentina and Australia, only a certain fraction of the harvesting area is irrigated, the actual which are the main exporting countries of these crops. irrigation water use is taken equal to this fraction times the irrigation water requirements. Concerning crop parameters, crop coefficients 2. Method and Data for different crops are taken from FAO (Allen et al., 1998; FAO, 2003a) and crop lengths from the work of Chapagain and Hoekstra (2004).In The selected crops are staple food crops with low economic value the case of the USA, the planting dates and cropping calendar are in the world market (125–240 US$/ton) and use the most water taken from USDA (2006). globally after rice (rice 21%, wheat 12, maize 9 and soybean 4) The ‘green’ virtual-water content of the crop has been estimated as (Chapagain and Hoekstra, 2004; Hoekstra and Chapagain, 2008). the ratio of the green water use to the crop yield (Chapagain et al., Major exporting countries were chosen for the study: USA, Argentina 2006b). The ‘blue’ virtual-water content of the crop has been taken and Canada, contributing 69% to the global exported maize, 63% to equal to the ratio of the volume of irrigation water used to the crop exported soybeans and, together with Australia, 58% to exported yield (ibid.). Both green and blue virtual-water contents have been wheat (Table 1). estimated separately by state or province. Then, national average The virtual-water content of a product is calculated using the green and blue virtual-water contents have been calculated on the methodology developed by Hoekstra and Hung (2002, 2005), basis of the respective share of each state or province to the national Chapagain and Hoekstra (2004) and Hoekstra and Chapagain (2007, production. The major crop producing states or provinces combined 2008). The virtual-water content of primary crops (m3/ton) has been accounted for about 90% of the total national production (Table 2). calculated as the ratio of the water volume used during the entire Data on average crop yield and production by state or province are period of crop growth (crop water requirement, m3/ha) to the taken from Statistics Canada (2007), USDA (2007), SAGPyA (2007) corresponding crop yield (ton/ha) in the producing country. The and USDA-FAS (2007), and data on international trade from the volume of water used to grow crops in the field has two components: FAOSTAT database (FAO, 2007b). In the case of the USA, winter and effective rainfall (green water) and irrigation water (blue water). spring wheat were separately calculated and weighted according to the The total crop water requirement, together with the effective share of each to the national production. The total virtual-water content rainfall and irrigation requirements per country have been estimated of primary crops is the sum of the green and blue components. using the CROPWAT model (Allen et al., 1998; FAO, 2003a). The In order to assess the virtual-water ‘flows’ between nations, the basic calculation is done using climate data for the major crop-producing approach has been to multiply international trade volumes (ton/year) states or provinces and a specific cropping pattern for each crop by their associated virtual-water content (m3/ton) for the 2000–2004 according to the type of climate (Tables 1 and 2). The climate data period. It is thus assumed that states or provinces within a country have been taken from the CLIMWAT model (FAO, 2003b) for the most contribute to the national export in proportion to their total production. appropriate climatic stations located in the major crop producing regions of each state or province (Table 2). For states or provinces 3. Proportion of Green Water in International Crop Trade with more than one climate station, the data for the relevant stations 3.1. Virtual-Water Content of Maize, Soybeans and Wheat in the Major Table 1 Exporting Countries Crop calendar, yield and production by country.