Water cycle and people: water for feeding humanity

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.