Abstract
Abstract. The aim of this study is to estimate the green, blue and grey water footprint of wheat in a spatially-explicit way, both from a production and consumption perspective. The assessment is global and improves upon earlier research by taking a high-resolution approach, estimating the water footprint of the crop at a 5 by 5 arc minute grid. We have used a grid-based dynamic water balance model to calculate crop water use over time, with a time step of one day. The model takes into account the daily soil water balance and climatic conditions for each grid cell. In addition, the water pollution associated with the use of nitrogen fertilizer in wheat production is estimated for each grid cell. We have used the water footprint and virtual water flow assessment framework as in the guideline of the Water Footprint Network. The global wheat production in the period 1996–2005 required about 108 billion cubic meters of water per year. The major portion of this water (70%) comes from green water, about 19% comes from blue water, and the remaining 11% is grey water. The global average water footprint of wheat per ton of crop was 1830 m3/ton. About 18% of the water footprint related to the production of wheat is meant not for domestic consumption but for export. About 55% of the virtual water export comes from the USA, Canada and Australia alone. For the period 1996–2005, the global average water saving from international trade in wheat products was 65 Gm3/yr. A relatively large total blue water footprint as a result of wheat production is observed in the Ganges and Indus river basins, which are known for their water stress problems. The two basins alone account for about 47% of the blue water footprint related to global wheat production. About 93% of the water footprint of wheat consumption in Japan lies in other countries, particularly the USA, Australia and Canada. In Italy, with an average wheat consumption of 150 kg/yr per person, more than two times the word average, about 44% of the total water footprint related to this wheat consumption lies outside Italy. The major part of this external water footprint of Italy lies in France and the USA.
Highlights
Fresh water is a renewable but finite resource
When we compare the computed green and blue water footprints to the computation by Siebert and Doll (2010), we find that their estimate of the total water footprint of global wheat production is 11% lower, which is completely due to their lower estimate of the green water footprint component
The major findings of the current study are that: (i) the green water footprint related to global wheat production is about four times larger than the blue water footprint, (ii) a large amount of global water saving occurs as a result of international trade in wheat products – without trade the global wheat-related water footprint would be 6% higher than under current conditions, (iii) the high share of blue water (48%) in the global water saving indicates that the water footprint of wheat in the largest virtual water export regions is dominated by green water while virtual water import regions depend more strongly on blue water for wheat production
Summary
Fresh water is a renewable but finite resource. Both freshwater availability and quality vary enormously in time and space. Growing populations coupled with continued socioeconomic developments put pressure on the globe’s scarce water resources. In many parts of the world, there are signs that water consumption and pollution exceed a sustainable level. The reported incidents of groundwater depletion, rivers running dry and worsening pollution levels form an indication of the growing water scarcity (Gleick, 1993; Postel, 2000; WWAP, 2009). Molden (2007) argues that to meet the acute freshwater challenges facing humankind over the coming fifty years requires substantial reduction of water use in agriculture The reported incidents of groundwater depletion, rivers running dry and worsening pollution levels form an indication of the growing water scarcity (Gleick, 1993; Postel, 2000; WWAP, 2009). Molden (2007) argues that to meet the acute freshwater challenges facing humankind over the coming fifty years requires substantial reduction of water use in agriculture
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