Water footprint benchmarks for crop production: A first global assessment

In the coming few decades, global freshwater demand will increase to meet the growing demand for food, fibre and biofuel crops. Raising water productivity in agriculture, that is reducing the water footprint (WF) per unit of production, will contribute to reducing the pressure on the limited global freshwater resources. This study establishes a set of global WF benchmark values for a large number of crops grown in the world. The study distinguishes between benchmarks for the green-blue WE (the sum of rain- and irrigation water consumption) and the grey WF (volume of polluted water). The reference period is 1996-2005. We analysed the spatial distribution of the green-blue and grey WFs of different crops as calculated at a spatial resolution of 5 by 5' with a dynamic water balance and crop yield model. Per crop, we ranked the WF values for all relevant grid cells from smallest to largest and plotted these values against the cumulative percentage of the corresponding production. The study shows that if we would reduce the green-blue WF of crop production everywhere in the world to the level of the best 25th percentile of current global production, global water saving in crop production would be 39% compared to the reference water consumption. With a reduction to the WF levels of the best 10th percentile of current global production, the water saving would be 52%. In the case that nitrogen-related grey WFs in crop production are reduced, worldwide, to the level of the best 25th percentile of current global production, water pollution is reduced by 54%. If grey WFs per ton of crop are further reduced to the level of the best 10th percentile of current production, water pollution is reduced by 79%. The benchmark values provide valuable information for formulating WE reduction targets in crop production. Further studies will be required to test the sensitivity of the benchmark values to the underlying model assumptions, to see whether regionalization of benchmarks is necessary and how certain WF benchmark levels relate to specific technology and agricultural practices. (C) 2014 The Authors. Published by Elsevier Ltd.