Ensuring that the world's food needs are met by 2050 will take a doubling of global food production. To improve agricultural yields on that scale will require a radical rethink of global water-management strategies and policies. Sub-Saharan Africa is the epicentre of this challenge. Ninety-five per cent of sub-Saharan agriculture depends on 'green water': moisture from rain held in the soil. In large parts of the continent, most rain evaporates before it generates 'blue water', or run-off, so little of it recharges rivers, lakes and groundwater.

Agricultural systems as well as other ecosystems generate ecosystem services, i.e., societal benefits from ecological processes. These services include, for example, nutrient reduction that leads to water quality improvements in some wetlands and climatic regulation through recycling of precipitation in rain forests.

A new concept,