Physical and virtual water transfers for regional water stress alleviation in China

Water can be redistributed through, in physical terms, water transfer projects and virtually, embodied water for the production of traded products. Here, we explore whether such water redistributions can help mitigate water stress in China. This study, for the first time to our knowledge, both compiles a full inventory for physical water transfers at a provincial level and maps virtual water flows between Chinese provinces in 2007 and 2030. Our results show that, at the national level, physical water flows because of the major water transfer projects amounted to 4.5% of national water supply, whereas virtual water flows accounted for 35% (varies between 11% and 65% at the provincial level) in 2007. Furthermore, our analysis shows that both physical and virtual water flows do not play a major role in mitigating water stress in the water-receiving regions but exacerbate water stress for the water-exporting regions of China. Future water stress in the main water-exporting provinces is likely to increase further based on our analysis of the historical trajectory of the major governing socioeconomic and technical factors and the full implementation of policy initiatives relating to water use and economic development. Improving water use efficiency is key to mitigating water stress, but the efficiency gains will be largely offset by the water demand increase caused by continued economic development. We conclude that much greater attention needs to be paid to water demand management rather than the current focus on supply-oriented management.The geographical mismatch between freshwater demand and available freshwater resources is one of the largest threats to sustainable water supply in China (1) and throughout the world. It is well-known that China has a temperate south and an arid north (2). The North China Plain shows the greatest water scarcity, with per capita water availability under 150 m³/y (3–5). At the same time, this area is home to 200 million people and provides more than one-half of China’s wheat and one-third of its maize (6). Recognizing such a mismatch, China has been developing over 20 major physical water transfer projects with a total length of over 7,200 km (6), including the world’s largest—the South–North Water Transfer Project (SNWTP) (7). Three routes are projected in the SNWTP, which will ultimately transfer 44.8 Gm³ water from the Yangtze River Basin to the Huang-Huai-Hai River Basin annually, of which 14.8 Gm³ is for the East Route, 13 Gm³ is for the Middle Route, and 17 Gm³ is for the West Route (7). After completion of the three routes, the transferred water is projected to amount to 30.5% of total water withdrawal in the Huang-Huai-Hai River Basin in 2012 (the latest available statistic) (8).Apart from these major physical water transfer projects, there is another solution to remedy regional water scarcity—so-called virtual water (9–11). The virtual water concept, first introduced by Allan (12), is the water required for the production of goods and services along their supply chains (13). Based on this concept, water-scarce regions import water-intensive products instead of producing them locally, thus conserving local water resources (12, 14). Because the SNWTP has proved highly controversial in its potential impacts on both exporting and importing river ecosystems and its huge capital cost (∼$60 US billion), scholars have suggested that the North China Plain should, instead, reduce the export of water-intensive products or even import virtual water from southern China (11, 13, 15–17). An important question is if such redistributions can be effective in mitigating regional water stress in China.To answer this question, we report here on our quantification of China’s physical and virtual water flows at the provincial level for the year 2007. We have used the most recent interregional trade data and evaluated the associated impacts on water stress. To calculate virtual water flows, we have calculated water use throughout the entire supply chain in China. The study focused on 30 provincial-level administrative regions (provinces, autonomous regions, and municipalities—for simplicity, they are referred to as provinces) (names are shown in SI Appendix, Fig. S1) in mainland China where data were available. The volume of physical water transfer for each province was acquired through the Water Resources Bulletin of the studied provinces (4). To study virtual water flows, we incorporated the direct water use of 30 economic sectors of each province into an environmental extended multiregion input–output (MRIO) model (18, 19) (Methods). An MRIO model distinguishes production structure, technology, and consumption for each study area and shows flows of goods and services between and within regions; thus, it is ideally suited for measuring interregional virtual water flows (20, 21). The virtual water trade generated by final consumption was evaluated using the emissions embodied in trade method (22). Water stress was evaluated using the water stress index (WSI) (10, 23, 24). Moderate, severe, and extreme water stresses occur when the ratio of the annual freshwater withdrawal to the renewable freshwater resource is 20–40%, 40–100%, and over 100%, respectively.