Under climate change, current rainfed crops may require irrigation to maintain reasonable productivity, and current irrigated crops may have a larger or smaller irrigation requirement (FAO, 2011). Doll (2002) predicted a slight increase in global crop water requirements, but significantly less than other comparable works which tend to estimate an increase by 5-20% (Fischer et al., Recently, climate projections to 2070-2099 by Zhang and Cai (2013) indicate contrasting results across countries: lower water requirements can be expected in some regions of the world such as Africa, Australia and China, while in regions such as Europe, North India, eastern South America and eastern United States higher crop water requirements are projected. These results are subject to the land use types (rainfed or irrigated) and the uncertainty involved in the assessment approaches.