Green and blue water accounting in the Limpopo and Nile Basins

Globally, most food is produced using soil moisture that comes from precipitation (i.e., “green” water). Moreover, most of the water that reaches plants in irrigated systems also stems from precipitation. Despite this, irrigation (or “blue”) water has typically been the focus for policy analysis, largely because it is possible for humans to manipulate blue water. This paper analyzes alternative water futures using a combined green and blue water accounting framework embedded within the water simulation components of IFPRI’s International Model for Policy Analysis of Agricultural Commodities and Trade (IMPACT). Future scenarios recently developed for the International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD) and other studies are assessed with respect to this adjusted green/blue water accounting framework. The results reveal that accounting explicitly for green water resources broadens the scope of options for decision-makers who are seeking to improve agricultural production in the face of rising food and energy prices, a degrading water and land resource base, and increasing demands. This analysis highlight the importance of green/blue water accounting and presents a wider range of agricultural science and technology policy options for increasing global crop productivity across a span of potential futures.