Tracking indirect water footprints, virtual water flows, and burden shifts related to inputs and supply chains for croplands: A case for maize in China

Increasing crop yields to ensure an adequate food supply under water and land scarcity is dependent on intensive agricultural inputs (such as fertilizers, pesticides, agri-films, or energy) which consume water resources and generate water pollution. However, the burden shifting of water quantity and quality stress from producers to importer and consumers through agricultural input production, trade, and consumption have been largely overlooked. Here, taking maize in China as the study case, we mapped step-by-step indirect water footprint (IWF) of maize production, virtual water (VW) flows related to inputs driven by maize consumption, and the resulting burden shifting of water quantity and quality. Bottom-up WF accounting approach was applied. The maize consumption was intercepted into two stages: the crop production stage (CPS) from raw materials to the farm, and the crop trade stage (CTS) from farm to fork. Results show that the national average blue and grey IWF of maize production was 3.91 and 26.86 m3/t, respectively. In the CPS, the input-related VW flowed from the west and east coast to the north. In the CTS, the VW flows from the north to the south. Blue and grey VW flows in CTS caused by secondary flows of VW in CPS accounted for 48% and 18% of the total flows, respectively. In total VW flows along the maize supply chain, 63% of blue VW and 71% of grey VW net exports occurred in the north of severe water scarcity and water pollution levels. The analysis highlights the impact of the crop supply chain on water quantity and water quality in the consumption of agricultural inputs, the importance of step-by-step supply chain analysis for regional crop water conservation management, and the urgent need for integrated management of agricultural and industrial water resources.