Virtual water: An unfolding concept in integrated water resources management

In its broadest sense, virtual water refers to the water required for the production of food commodities. Issues relating to virtual water have drawn much attention in scientific communities and the political sphere since the mid 1990s. This paper provides a critical review of major research issues and results in the virtual water literature and pinpoints the remaining questions and the direction of research in future virtual water studies. We conclude that virtual water studies have helped to raise the awareness of water scarcity and its impact on food security and to improve the understanding of the role of food trade in compensating for water deficit. However, the studies so far have been overwhelmingly concerned with the international food trade, and many solely quantified virtual water flows associated with food trade. There is a general lack of direct policy relevance to the solutions to water scarcity and food insecurity, which are often local, regional, and river basin issues. The obscurity in the conceptual basis of virtual water also entails some confusion. The methodologies and databases of the studies are often crude, affecting the robustness and reliability of the results. Looking ahead, future virtual water studies need to enhance the policy relevance by strengthening their linkages with national and regional water resources management. Meanwhile, integrated approaches taking into consideration the spatial and temporal variations of blue and green water resources availability and the complexity of natural, socioeconomic, and political conditions are necessary in assessing the trade-offs of the virtual water strategy in dealing with water scarcity. To this end, interdisciplinary efforts and quantitative methods supported by improved data availability are greatly important.