Green and blue water use for agricultural production: Volumes and efficiencies

This chapter analyzes the evolution of water footprint associated to four major crops to define trends of water use and efficiency in agriculture. In particular, the separation of water use by source is considered, differentiating between green water (soil moisture originated from precipitation) and blue water (withdrawals from surface- and ground-water). Blue water contributes to about 10% of the total (green + blue) water footprint; however, it is central for humanity as it provides 42% of the global food production. The chapter focuses on the spatial and temporal variability of the blue water use and on the different role played by climate and anthropic factors in the definition of blue as well as total crop water footprint through a sensitivity analysis. The chapter presents the results about the variability in space of crop water footprint (green and blue) using maize to exemplify the discussion.