Spatiotemporal variations and developments of water footprints of pig feeding and pork production in China (2004-2013)

The production of nutrient-rich livestock products consumes large volumes of water while polluting aquatic systems; however, there has been little quantitative research globally on the spatiotemporal evolution of both water consumption and water pollution (based on the water footprint [WF]) for livestock products at an intra-national scale. Here we quantified the annual green, blue, and gray WFs for pig feeding and pork production, as the most important animal product in China, at the province scale in mainland China over 2004-2013, and distinguished four farming scales: scatter-feed, small-scale, medium-scale, and large-scale. The gray WF estimation is more comprehensive that pollutants in pig excreta is considered. Over the study period, the average unit consumptive (green-blue) and degradative (gray) WF of pig was 349 m(3) head(-1) and 206 m(3) head(-1), respectively. The average total consumptive and degradative WF of pig was 225.8 Gm(3) year(-1) and 133.2 Gm(3) year(-1), respectively, in China. Over time, the consumptive WFs of pig and pork increased (unit WF of pig: 8%; total WF of pig: 25 %; total WF of pork: 8%). The unit and annual gray WFs of pig increased 1% and 14 %, respectively, while the gray WF of pork remained unchanged. Spatially, there was a southward shift in provinces with large WFs over the study period. Overall, the green WF comprised a small proportion of the total WF than the blue WF. Regarding farming scales, scatter-feed systems had larger unit WFs of pigs and pork, whereas large-scale systems had the smallest unit WFs. These findings suggest that establishment of pig farms in mountainous regions far from residential areas, wider adoption of large-scale production, local cultivation of feed crops with lower WF near pig farms, and use of pig excreta as crop fertilizer would be the most conducive to water saving and quality control in China.