High-resolution water footprints of major crops in China from cities to grids

Rapid population and economic growth have led to an increased demand for water and food, thereby exacerbating the water scarcity crisis. Therefore, an objective assessment of water usage in crop production is crucial for ensuring national food security and alleviating water scarcity. However, the city-scale crop production water footprint (CWF) in China remains incomplete, while grid-scale CWF data are plagued by the limitations of coarse crop statistics. To fill this knowledge gap, we propose a novel methodology for developing a high-resolution inventory of CWFs. Based on this methodology, we quantified the city-scale water footprint (WF) of three major crops (rice, wheat, and maize) in China and allocated the CWFs of individual cities to 3 km × 3 km grids through a top-down downscaling approach to create a high-resolution CWF inventory. The results show that the average annual CWF of the three crops from 2000 to 2020 was in the order of rice (2.50 × 10¹² m³), maize (1.55 × 10¹² m³), and wheat (1.21 × 10¹² m³). During the study period, the dependence on green water resources for crop production in China increased, especially for maize, which showed a relative increase of 106.76% in green water demand, in addition to optimal water use efficiency, with the dual advantages of combining high yield and low irrigation dependence. At a grid scale of 3 km × 3 km, the CWFs of the three crops followed the same order as at the city scale. Furthermore, the green water footprint (GWF) of each of the three crops increased at different rates during the study period, with maize showing a particularly significant increase of 59.26%. Meanwhile, the blue water footprint (BWF) per unit area for rice and wheat increased, while the BWF for maize decreased by 0.94%. This finding implies that maize cultivation is more efficient in utilizing rainwater resources, thereby reducing dependence on blue water. The inventory established in this study can assist in optimizing crop production in various regions of China, thereby mitigating the effects of water scarcity and facilitating sustainable agricultural development.