『Summary
Recent developments of global models and data sets enable a new,
spatially explicit and process-based assessment of green and blue
water in food production and trade. An initial intercomparison
of a range of different (hydrological, vegetation, crop, water
resources and economic) models, confirms that green water use
in global crop production is about 4-5 times greater than consumptive
blue water use. Hence, the full green-to blue spectrum of agricultural
water management options needs to be used when tackling the increasing
water gap in food production. The different models calculate considerable
potentials for complementing the conventional approach of adding
irrigation, with measures to increase water productivity, such
as rainwater harvesting, supplementary irrigation, vapour shift
and soil and nutrient management. Several models highlight Africa,
in particular sub-Saharan Africa, as a key region for improving
water productivity in agriculture, by implementing these measures.
Virtual water trade, mostly based on green water, helps to close
the water gap in a number of countries. It is likely to become
even more important in the future, when inequities in water availability
are projected to grow, due to climate, population and other drivers
of change.
Further model developments and a rigorous green-blue water model
intercomparison are proposed, to improve simulations at global
and regional scale and to enable tradeoff analyses for the different
adaptation options.
Keywords: Green/blue water; Virtual water; Crop water productivity;
Irrigated/rainfed agriculture; Africa; Global model intercomparison』
Introduction
Box 1
The models
Main findings
Dominance of green water in food production
Overexploitation of water resources
Current and future water productivity/virtual water content
Adaptation options to increasing water scarcity and for food
security
Intensification on existing agricultural land
Irrigation
Rainwater harvesting, storage and supplementary irrigation
Improved soil and water management
Investment in agricultural water management
Area expansion onto non-agricultural land
Virtual water trade
Green and blue water use and potential in Africa
Discussion
Conclusions
References