Abstract: Water is the prime limiting factor in grain production in China. Agricultural water withdrawal has been under ever growing pressures in the context of population growth, economic development, urbanization process, diet change, and ecosystem preservation. However, to realize the national strategic goal of food security requires more grains to be produced, and consequently, does demand more water to be consumed. Hence, how to resolve the competing claims for water by various sectors while retaining adequate water for grain production will be the major challenge presenting to both researchers and decision makers. The paper firstly reviewed the state-of-the-arts ideas, concepts, and mindsets that had been emerged and developed in global water communities in the last 20 years, from which a paradigm shift in which green water and blue water lie at the center was identified and presented. Then, based on the “Broadly-defined Available Water for Agriculture (BAWA)” incorporating both green (i.e. cropland irrigation) and blue water (i.e. cropland precipitation) components, agricultural water use, consumption, and productivity were analyzed over a 15-year period from 1998 to 2012. Next the “Baselines for Agricultural Water Use” was proposed and proactively defined, in which blue water component was derived by projecting historical crop water productivity onto 2020. The green water component was likewise determined by using projection of last 15-year BAWA. The results showed that the redlines for blue water withdrawal in terms of assuring 550 million tons of grains to the year 2020 was 380 km³, while the green water component of the redlines was 450 km³. The paper proposed a set of policies in implementing the redlines, including conserving arable land and improving arable land infrastructure, building a sound-developed system for measuring and monitoring blue and green water, developing a water-adapted farming system, improving crop water productivity, and adopting basin- and region-scale water saving practices. The conclusion of the paper will also have implications for recent policy directives issued by China Ministry of Agriculture to combat agriculture-derived pollution in rural areas, “one control, two abatements, and three basic requirements”, of which one control means the definition of baseline agricultural water withdrawals and water use efficiency.

Key words: food security, Broadly-defined Available water for Agriculture (BAWA), crop water productivity, green water, blue water