this result is expected as grains and oil crops account for the largest portion of international trade and most of the traded grains and oil crops are produced in rainfed regions of the major trading countries schultz et al some of the authors have suggested also that trading green virtual water is more sensible than trading blue virtual water because the opportunity cost of green water is less than that of blue water yang et al in addition some authors have suggested that trading green water for blue water can generate meaningful water savings from a global perspective the bluegreen metaphor provides helpful descriptive terminology but there is no inherent underlying principle that can be called upon to suggest optimal production or trading strategies