Drops for crops: modelling crop water productivity on a global scale

There is an emerging need to support water and food policy and decision making at the global
and national levels. A systematic tool that is capable of analyzing water-food relationships
with high spatial resolutions would be very useful. A GEPIC model has recently been
developed by integrating a crop growth model with a Geographic Information System (GIS).
The GEPIC model was applied to simulate crop yield and crop water productivity (CWP) for
maize at a spatial resolution of 30 arc-minutes on a global scale. A comparison between
simulated yields and FAO statistical yields in 124 countries shows a good agreement. The
simulated CWP values are mainly in line with the measured values reported in literature. The
crop yield and CWP were simulated with the assumption of sufficient water and fertilizer
supply, holding other factors unchanged. The simulation results show that many countries
have the potentials in achieving high maize yields and CWP. More than 80% of African
countries have the potential to double their CWP. This reflects the current poor water and
fertilizer management there. The results imply that efforts have to be strengthened to improve
water and fertilizer management should the malnutrition be reduced or even eliminated.