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Abstract
The distinction of ‘blue’ (liquid) and ‘green’ (vapour) water flow is introduced to make possible an
assessment of water flows to be appropriated for future food production. The author offers a
‘backcasting approach’ in assessing the consumptive water requirements for feeding humanity by 2050
and from where the needed water may be provided (irrigation, crop-per-drop improvements and
horizontal expansion into grasslands and forests). She concludes that food security will demand a major
shift in thinking.