Assessment of regional crop-related physical-virtual water coupling flows

Agriculture is the sector with the largest water usage globally, as well as within China. Water is a limited resource that represents the base for regional food security. Modern water science has revealed that crop production consumes not only so-called blue water (surface and ground water), which is at the core of current agricultural water policies, but also so-called green water (rainwater). As driven by natural-socio-economic (“ternary”) activities, water related to the crop production chain (i.e. pre-, during- and after-production) flows in coupled physical and virtual (the “two-dimension”) forms through physical water consumption, virtual water embedding and inter-regional virtual water flows. In this work, based on a physical-virtual water flow theory framework, we have developed a quantification approach for regional crop-related physical-virtual water flow processes, with a focus on the water quantity. This quantification integrates green and blue water footprint accounting and virtual water flow network simulations. We applied this approach in a case study for six western provinces along the “Silk Road Economic Belt” in China over the period 1985−2013. Ten major crops were considered in the case study. Our results show significant crop-related physical-virtual water flows among the six provinces. In terms of blue water, 49% of the irrigation water supply was consumed in the crop production we considered, 31% of which was converted to virtual water flows. Moreover, we find that a trade-off exists between water use efficiency and associated economic value along the physical-virtual water flows. For example, Xinjiang has suffered water stress due to crop production, with a net virtual water export of 21×10⁹ m³/a, but has a high economic income of 314 million CNY/a as a result of the water flow. This study highlights the importance and necessity of improving traditional agricultural water management, which focuses on reducing blue water consumption through engineering strategies, by integrating physical-virtual water flow assessments in order to achieve both high resources and economic efficiencies in water use, as well as both green and blue water savings. Specifically, we propose three key steps towards attaining this goal: (1) To consider both the physical and virtual water flows in modern agriculture water saving technologies as well as policies; (2) to invest in and enhance academic capabilities for quantifying, analysing and optimizing agricultural physical-virtual water flows; (3) to build a modern agricultural water management system targeted towards healthy and sustainable physical-virtual water flows in order to finally achieve both water sustainability and food security goals.