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.
