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Growing world population and the uncertain hazards that accompany climate change put an increasing pressure on the management and sustainability of scarce environmental resources, notably water. In spite of its water scarcity, the state of Arizona permits as much as 73% of its water to be consumed by a single sector, crop production. Since 79% of such crop production is not consumed in Arizona, it corresponds to exporting up to 67% of the water available in the state to the rest of the country and abroad. It has certain and glooming consequences on the availability of water for a state expected to see its population grow and its climate get drier. Based on input-output techniques, we simulate three scenarios aiming at saving 19% of the water available, a figure set by the first of them based on improving the efficiency of the current irrigation system. The same savings could also be reached by a twenty-seven-fold increase in the price of water or a 19.5% reduction in crop exports. Estimates indicate that the least costly solution is a more efficient irrigation system while export reduction is the second-best choice.

There is an exhaustive literature on Israel, Palestine and water, which has documented how the asymmetric power of Israel in the Oslo negotiations ensured its control of land and water over Palestine. Less attention however has been paid on the interface of water, trade and agriculture, and the ways in which controlling trade, Israel controlled the virtual flows of water too. The concept of virtual water makes the water-agriculture-trade relationship visible, shedding light on agricultural trade flows in terms of water. Applying a political ecology approach, this paper shows how socio-ecological conditions are sustained by and organised through both social and metabolic-ecological processes. A biophysical analysis - the agricultural flows of virtual water from and to Palestine in the Post-Oslo period - is combined with the examination of the power relations that governed these flows. The analysis reveals that virtual water flows are not static but instead evolve within the (geo)political-economic context in which they are embedded, bringing to light Israel's control over the flow of Palestinian agricultural virtual water. We argue that a political ecology approach to virtual water offers a theoretical basis to move beyond the currently techno-managerial emphasis in the virtual water literature, illuminating the link between the control of virtual flows and the consolidation of political and economic power.

The countries in the Mediterranean basin increasingly specialized in Mediterranean agricultural products for exports throughout the twentieth century. In this context, the main objective of this paper is to quantify and discuss on the impacts that this growing Mediterranean exports specialization generated on water resources over the last century. To that aim, we focus on the water embodied in Mediterranean exports, the trends followed by dams' construction and the area equipped for irrigation as well as on the evolution of blue water stress. Our findings point at an intense expansion of Mediterranean virtual water exports between 1910 and 2010 that went along with the construction of water infrastructure. It enabled water-intensive crops to be grown in arid regions, but also, exacerbated blue water stress. We also find important regional divergences, highlighting the role of Spain as a super exporter of Mediterranean crops. Finally, we observe that the trends and patterns of trade flows and the subsequent pressures on water resources are highly conditioned by political, economic and technological developments.

In this paper, we employ a new approach to assessing the impact and efficiency of virtual water use along the supply chain. This approach involves estimating the economic value of virtual water flows. A realistic tea supply chain case study is presented to test this new approach and compare it with alternative volumetric and stress-weighted methods. The case study is used to highlight the total value of the blue and grey water used to produce 1 tonne of tea as a finished good ($224). The case study also illustrates how variations in the relative unit value of water between geographies, in this case between multiple locations where crops are cultivated (India $0.08 m3, Indonesia $0.09 m3 and Kenya $0.27 m3), can be used to inform supply chain optimisation and allocative efficiency. Indeed, the case study suggests that taking into account the economic value of virtual water may provide differing prescriptions for the sustainable management of supply chains when compared to the traditional volumetric water footprint, and the stress-weighted water footprint used in LCA.

International trade of agricultural goods impacts local water scarcity. By quantifying the effect of trade on crop production on grid-cell level and combining it with cell- and crop-specific virtual water contents, we are able to determine green and blue water consumption and savings. Connecting the information on trade-related blue water usage to water shadow prices gives us the possibility to value the impact of international food crop trade on local blue water resources. To determine the trade-related value of the blue water usage, we employ two models: first, an economic land- and water-use model, simulating agricultural trade, production and water-shadow prices and second, a global vegetation and agricultural model, modeling the blue and green virtual water content of the traded crops. Our study found that globally, the international trade of food crops saves blue water worth 2.4 billion US$. This net saving occurs despite the fact that Europe exports virtual blue water in food crops worth 3.1 billion US$. Countries in the Middle East and South Asia profit from trade by importing water intensive crops, countries in Southern Europe on the other hand export water intensive agricultural goods from water scarce sites, deteriorating local water scarcity.

China's booming economy has brought increasing pressures on its water resources. The water scarcity problem in China is characterized by a mismatch between the spatial distributions of water resources, economic development and other primary factors of production, which leads to the separation of production and consumption of water-intensive products. In this paper, we quantify the scale and structure of virtual water trade and consumption-based water footprints at the provincial level in China based on a multi-regional input–output model. We found that virtual water withdrawals and consumption embodied in domestic trade amounts to 184 billion m3 and 101 billion m3 in 2007, respectively, which is equivalent to 38% and 39% of national total fresh water withdrawals and consumption, respectively. Virtual water trade embodied in domestic trade is about two times as much as virtual water embodied in China's international exports. Water footprint in all four municipalities, i.e., Beijing, Tianjin, Shanghai and Chongqing, depends heavily on virtual water inflow from other provinces. China has a north-to-south net VWT pattern which is roughly the opposite of the distribution of its water resources. In addition to water efficiency improvement measures, re-shaping the water-trade nexus can be a significant complementary tool to address local water scarcity problems.

This paper aims to analyse the impact on water consumption of trade expansion in the first era of globalisation. To that end, we have chosen the case of Spain, a semi-arid country with significant cyclical water shortages. More specifically, we are interested in answering the following questions. What volume of water was required for exports of agricultural and food products? How did this variable evolve over time? Which factors drove this evolution? In short, we wish to understand the impact on water resources of Spain's entry into world agriculture and food markets. Firstly, we examine virtual water trade flows in the long run. Secondly, we attempt to disentangle certain major driving forces underlying these trajectories. In order to establish the role played by trade in the final net balance of water, a Decomposition Analysis (DA) is applied. Our findings show the great pressures that the first globalisation imposed on not only domestic but also foreign water resources. Trade volumes as well as trade patterns were essential factors driving rising virtual water flows, while yield improvements contributed smoothly to moderation in the expansion of water flows.

Recent analyses of the evolution and structure of trade in virtual water revealed that the number of trade connections and volume of virtual water trade have more than doubled over the past two decades, and that developed countries increasingly import water embodied in goods from the rest of the world to alleviate pressure on domestic water resources. At the same time, as demand continues to increase and climate change threatens to alter hydrological cycles, water scarcity is a growing problem. Does research into virtual water trade need to consider water scarcity and differentiate flows out of water-scarce regions from flows out of water-abundant regions? Previous studies sum and compare virtual water volumes originating in countries experiencing vastly different degrees of water scarcity. We therefore incorporate water scarcity into an assessment of global virtual water flows. We use input–output analysis to include indirect virtual water flows. We find that the structure of global virtual water networks changes significantly after adjusting for water scarcity.

Sustainability as a concept has multiple disparate perspectives stemming from different related disciplines which either maintain ambiguous interpretations or concentrate on metrics pertaining to single aspects of a system. Given the embedded multi-dimensionality of sustainability, systemic approaches are needed that can cope with interactions of different dimensions. Past efforts for measuring sustainability holistically have taken an accounting approach based on the availability and efficiency of resource flows. However, an accounting approach fails to fully incorporate the intensive parameters pertaining to sustainability. An ecological information-based approach is a promising holistic measurement which incorporates both intensive and extensive dimensions of sustainability. This paper evaluates this approach by applying it to six economic resource trade flow networks: virtual water, oil, world commodity, OECD + BRIC commodity, OECD + BRIC foreign direct investment, and iron and steel. From the perspective of biomimicry, it appears that these networks can achieve higher levels of efficiency without weakening their robustness to resource delivery. The trends of measured efficiency and redundancy of the studied networks are demonstrated to be useful in reflecting long term changes while the trend in robustness levels were found to exhibit similar behavior to an ecosystem in its early phase of development.

Virtual water trade is increasingly recognized as a useful metaphor for thinking about freshwater resources in an international context. Its legitimacy in terms of economic theory has been questioned by a number of authors, however. In this article I develop new theoretical results that place the virtual water concept on a firm economic foundation, and which correct several misconceptions within the existing literature on virtual water economics.

Beijing is under severe water resource pressure due to the rapid economic development and growing population. This study quantitatively evaluates the water footprint of Beijing in an interregional input–output framework with a focus on blue water resources and uses. The inter-connections of water resources between Beijing and other provinces are analyzed with a sectoral specification. The results show that the total water footprint of Beijing is 4498.4 10 6 m 3 /year, of which 51% is from the external water footprint acquired through virtual water import. Agriculture has the highest water footprint of 1524.5 10 6 m 3 /year with 56% coming from external sources. The main virtual water provider for Beijing is Hebei, another water scarce region, from which Beijing receives virtual water of 373.3 10 6 m 3 /year with 40% from agriculture. The results of this study suggest that the interregional trade coordination, especially for the main sectors with high water use intensity, is important for enhancing the efficiency of regional and national water resource utilization.

The paper makes a global assessment of the green, blue and grey water footprint of rice, using a higher spatial resolution and local data on actual irrigation. The national water footprint of rice production and consumption is estimated using international trade and domestic production data. The global water footprint of rice production is 784 km3/year with an average of 1325 m3/t which is 48% green, 44% blue, and 8% grey. There is also 1025 m3/t of percolation in rice production. The ratio of green to blue water varies greatly over time and space. In India, Indonesia, Vietnam, Thailand, Myanmar and the Philippines, the green water fraction is substantially larger than the blue one, whereas in the USA and Pakistan the blue water footprint is 4 times more than the green component. The virtual water flows related to international rice trade was 31 km3/year. The consumption of rice products in the EU27 is responsible for the annual evaporation of 2279 Mm3 of water and polluted return flows of 178 Mm3 around the globe, mainly in India, Thailand, the USA and Pakistan. The water footprint of rice consumption creates relatively low stress on the water resources in India compared to that in the USA and Pakistan. Research Highlights ► It is a global assessment of the green, blue and grey water footprint of rice. ► The global water footprint of rice is 784 km3/year with an average of 1325 m3/t. ► There is an average additional 1025 m3/t of percolation in rice production. ►The shares of green, blue and grey water footprint are 48%, 44% and 8%. ► The virtual water flows related to international rice trade is 31 km3/year.

Using the Heckscher-Ohlin trade model, I refute two prominent but incorrect claims on virtual water trade. These claims are that virtual water trade (i) levels uneven water distribution, and (ii) reduces the potential for water conflict. Both claims are based on an incorrect understanding of comparative advantage in the production of water-intensive goods. The results show that both claims only hold under certain conditions, but do not necessarily follow from the Heckscher-Ohlin trade model. © 2010 Elsevier B.V.

Virtual water is the volume of water used to produce a commodity or service. Hitherto, most virtual water 'trade' studies have focused on its potential contribution to saving water, especially in water short regions. Very little, however, has been said about the opportunity cost of the associated water. The present research critically evaluates the strategic importance of green water (soil water originating from rainfall) in relation to 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 (irrigation with water abstracted from ground or surface water systems). Although it is widely known that major grain exporters - the USA, Canada, France, Australia and Argentina - produce grain in highly productive rain-fed conditions, green water volumes in exports have rarely been estimated. The present study corroborates that green water is by far the largest share of virtual water in maize, soybean and wheat exports from its main exporting countries (USA, Canada, Australia and Argentina) during the period 2000-2004. Insofar virtual water is 'traded' towards water-scarce nations that heavily depend on their blue water resources, green virtual-water '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.

This study quantifies the external water footprint of the Netherlands by partner country and import product and assesses the impact of this footprint by contrasting the geographically-explicit water footprint with water scarcity in the different parts of the world. The total water footprint of the Netherlands is estimated to be about 2300 m3/year/cap, of which 67% relates to the consumption of agricultural goods, 31% to the consumption of industrial goods, and 2% to domestic water use. The Dutch water footprint related to the consumption of agricultural goods, is composed as follows: 46% related to livestock products; 17% oil crops and oil from oil crops; 12% coffee, tea, cocoa and tobacco; 8% cereals and beer; 6% cotton products; 5% fruits; and 6% other agricultural products. About 11% of the water footprint of the Netherlands is internal and 89% is external. Only 44% of virtual-water import relates to products consumed in the Netherlands, thus constituting the external water footprint. For agricultural products this is 40% and for industrial products this is 60%. The remaining 56% of the virtual-water import to the Netherlands is re-exported. The impact of the external water footprint of Dutch consumers is highest in countries that experience serious water scarcity. Based on indicators for water scarcity the following eight countries have been identified as most seriously affected: China; India; Spain; Turkey; Pakistan; Sudan; South Africa; and Mexico. This study shows that Dutch consumption implies the use of water resources throughout the world, with significant impacts in water-scarce regions.

Virtual water adds a new dimension to international trade, and brings along a new perspective about water scarcity and water resource management. Most virtual water literature has focused on quantifying virtual water “flows” and on its application to ensure water and food security. Nevertheless, the analysis of the potential gains from international trade, at least from a water resources perspective, needs to take into account both spatial and temporal variations of blue (groundwater and stream flow) and green (soil moisture) water, as well as the socioeconomic and policy conditions. This paper evaluates whether Spanish international trade with grains is consistent with relative water scarcity. For this purpose, the study estimates the volume and economic value of virtual water “flow” through international grain trade for the period 1997–2005, which includes 3 years with different rainfall levels. The calculations show that Spain is a net virtual water “importer” through international grain trade. The volume of net virtual water “imports” amounts to 3420, 4383 and 8415 million m 3 in wet (1997), medium (1999) and dry (2005) years, respectively. Valuing blue water at its shadow price or scarcity value, blue water “exports” oscillate between 0.7 and 34.2 million Euros for a wet and dry year, respectively. Overall, grain trade is apparently consistent with relative water scarcity as net imports increase in dry years. However, the evolution of grain exports, expressed as a variation in quantity and volume, does not match the variations in resource scarcity. A disaggregated crop analysis reveals that there are other factors, such as quality, product specialization or the demand for a standardized product, which also influence trade decisions and are not included in the notion of virtual water. These facts, among others, can therefore create potential distortions in the application of virtual water to the analysis of specific trade patterns. Nevertheless, from a water resources perspective, virtual water can bring important insights across countries for improving water and land management globally, fostering adaptation strategies to climate change and to transboundary resource management.

Research on the flow of virtual water associated with agricultural crop production and trade has focussed almost entirely on water quantity. It is pertinent to consider and quantify the opportunity costs in terms of reduced water quality associated with crop production. This paper investigates the impacts of water quality on virtual water trading by creating a proxy for water quality impacts by calculating the amount of water required to dilute nonpoint-source agrochemical inputs to relevant water quality guideline values. The quantity of water required for dilution of five agrochemicals (two nutrients; nitrogen and phosphorus and three insecticides; azinphos-methyl, chlorpyrifos and endosulfan) was estimated for five crops in South Africa (maize, wheat, sugar cane, citrus and cotton) and compared to consumption of irrigation water (blue water) and rainfall (green water) for the same crops. Results indicate that the volume of water required for dilution is similar to the total sum of green and blue water required for crop production, but significantly greater than blue water use (irrigation use). For all crops phosphorus losses require greater amounts of water for dilution than for nitrogen, while pesticides result in the greatest water quality use. Estimates of water quality use are based on assumptions for a number of input variables (i.e. fertilizer application rates, percentage loss of agrochemicals from cropped areas). A Monte Carlo analysis (5000 iterations) was run to randomly select input variables from within defined ranges. Water quality use was calculated and expressed as a factor of blue water use. For all crops the average factor indicated that the volume of water required for dilution of all agrochemicals was greater than that required for irrigation. The results of this study clearly indicate that the impacts of agriculture on water quality need to be considered in virtual water trading scenarios. The incorporation of a method to predict impacts on water quality provides a comparative tool which generates a more holistic frame of reference for decision making with regard to impacts on the water resource and virtual water trading.

The water footprint concept introduced in 2002 is an analogue of the ecological footprint concept originating from the 1990s. Whereas the ecological footprint (EF) denotes the bioproductive area (hectares) needed to sustain a population, the water footprint (WF) represents the freshwater volume (cubic metres per year) required. In elaborating the WF concept into a well-defined quantifiable indicator, a number of methodological issues have been addressed, with many similarities to the methodological concerns in EF analysis. The methodology followed in WF studies is in most cases analogous to the methodology taken in EF studies, but deviates at some points. Well-reasoned it has been chosen for instance to specifically take into account the source and production circumstances of products and assess the actual water use involved, thus not taking global averages. As a result one can exactly localise the spatial distribution of a water footprint of a country. With respect to the outcome of the footprint estimates, one can see both similarities and striking differences. Food consumption for instance contributes significantly to both the EF and the WF, but mobility (and associated energy use) is very important only for the EF. From a sustainability perspective, the WF of a country tells another story and thus at times will put particular development strategies in a different perspective. The paper reviews and compares the methodologies in EF and WF studies, compares nation's footprint estimates and suggests how the two concepts can be interpreted in relation to one another. The key conclusion is that the two concepts are to be regarded as complementary in the sustainability debate.

The main idea of this paper is to analyse the relationships between the productive process and the commercial trade with water resources used by them. For that, the first goal is to find out, by means of the estimation of virtual water, the exported crops which have the highest water consumption. Similarly, we analyse the crops that are imported and therefore, might contribute to save water. The second objective is to put forward new ways to save water by means of the virtual water trade. This first conclusion contradicts not only the comparative advantages theory but also the environmental sustainability logic. The previous conclusion is derived from the great exports of water via potatoes and vegetables, and also via citrus fruit and orchards; and, on the other hand, from the imports, such as cereals and arable crops, with lower water requirements. The second conclusion affirms as Andalusia utilises large amounts of water in its exports, and in turn, it does not produce goods with low water requirements, the potential saving would be very significant if the terms of our trade were the other way round. We are convinced that the agricultural sector must modify the use of water to a great extent in order to reach significant water savings and an environmental sustainability path.

The success of China's economic development has left deep marks on resource availability and quality. Some regions in China are relatively poor with regards to water resources. This problem is exacerbated by economic growth. Flourishing trade activities on both domestic and international levels have resulted in significant amounts of water withdrawal and water pollution. Hence the goal of this paper is to evaluate the current inter-regional trade structure and its effects on water consumption and pollution via 'virtual water flows'. Virtual water is the water embedded in products and used in the whole production chain, and that is traded between regions or exported to other countries. For this assessment of trade flows and effects on water resources, we have developed an extended regional input-output model for eight hydro-economic regions in China to account for virtual water flows between North and South China. The findings show that the current trade structure in China is not very favorable with regards to water resource allocation and efficiency. North China as a water scarce region virtually exports about 5% of its total available freshwater resources while accepting large amounts of wastewater for other regions' consumption. By contrast, South China a region with abundant water resources is virtually importing water from other regions while their imports are creating waste water polluting other regions' hydro-ecosystems. (c) 2006 Elsevier B.V. All rights reserved.

The consumption of a cotton product is connected to a chain of impacts on the water resources in the countries where cotton is grown and processed. The aim of this paper is to assess the ‘water footprint’ of worldwide cotton consumption, identifying both the location and the character of the impacts. The study distinguishes between three types of impact: evaporation of infiltrated rainwater for cotton growth (green water use), withdrawal of ground- or surface water for irrigation or processing (blue water use) and water pollution during growth or processing. The latter impact is quantified in terms of the dilution volume necessary to assimilate the pollution. For the period 1997–2001 the study shows that the worldwide consumption of cotton products requires 256 Gm3 of water per year, out of which about 42% is blue water, 39% green water and 19% dilution water. Impacts are typically cross-border. About 84% of the water footprint of cotton consumption in the EU25 region is located outside Europe, with major impacts particularly in India and Uzbekistan. Given the general lack of proper water pricing mechanisms or other ways of transmitting production-information, cotton consumers have little incentive to take responsibility for the impacts on remote water systems.

Understanding the relationship between drought and population dynamics is increasingly important, particularly in areas where high population growth corresponds with increasing drought risk due to climate change. We examine the relationship between drought events and population dynamics using a stylized hydrology-demography model that has been calibrated to simulate plausible feedbacks for the population decline of the Ancient Maya of Central America. We employ a deterministic and a stochastic approach. We find that the impact of drought increases abruptly once a critical threshold of population density is exceeded. The critical threshold depends on the intensity and duration of the drought as well as on the level of technology adopted by society, the extent of markets and societal behavior. The simulations show that, for a society to be as food secure post-climate change as they are pre-climate change, strategies would have to be adopted to not only increase the region's capacity to provide sufficient resources for its growing population, but also to buffer the impact of a drier climate on productivity. This study provides suggestions on how technological, societal and economic development can modify the system to mitigate the impacts of climate change on the human population.