Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544;
Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan;
Proc Natl Acad Sci U S A. 2014 Jul 8;111(27):9774-9. doi: 10.1073/pnas.1404749111. Epub 2014 Jun 23.
China's water resources are under increasing pressure from socioeconomic development, diet shifts, and climate change. Agriculture still concentrates most of the national water withdrawal. Moreover, a spatial mismatch in water and arable land availability--with abundant agricultural land and little water resources in the north--increases water scarcity and results in virtual water transfers from drier to wetter regions through agricultural trade. We use a general equilibrium welfare model and linear programming optimization to model interprovincial food trade in China. We combine these trade flows with province-level estimates of commodities' virtual water content to build China's domestic and foreign virtual water trade network. We observe large variations in agricultural water-use efficiency among provinces. In addition, some provinces particularly rely on irrigation vs. rainwater. We analyze the virtual water flow patterns and the corresponding water savings. We find that this interprovincial network is highly connected and the flow distribution is relatively homogeneous. A significant share of water flows is from international imports (20%), which are dominated by soy (93%). We find that China's domestic food trade is efficient in terms of rainwater but inefficient regarding irrigation, meaning that dry, irrigation-intensive provinces tend to export to wetter, less irrigation-intensive ones. Importantly, when incorporating foreign imports, China's soy trade switches from an inefficient system to a particularly efficient one for saving water resources (20 km(3)/y irrigation water savings, 41 km(3)/y total). Finally, we identify specific provinces (e.g., Inner Mongolia) and products (e.g., corn) that show high potential for irrigation productivity improvements.
中国的水资源正面临着社会经济发展、饮食结构变化和气候变化带来的越来越大的压力。农业仍然集中了全国大部分的取水量。此外，水和耕地资源的空间不匹配——北方农业土地丰富但水资源匮乏——加剧了水资源短缺，并导致通过农业贸易将虚拟水从干旱地区转移到湿润地区。我们使用一般均衡福利模型和线性规划优化来模拟中国的省际粮食贸易。我们将这些贸易流量与各省商品虚拟水含量的估计值结合起来，构建了中国国内和国外的虚拟水贸易网络。我们观察到各省农业用水效率存在很大差异。此外，一些省份特别依赖灌溉用水而不是雨水。我们分析了虚拟水流模式及其对应的节水效果。我们发现，这个省际网络高度互联，流量分布相对均匀。相当一部分水流来自国际进口（20%），其中大豆（93%）占主导地位。我们发现，就雨水而言，中国国内的粮食贸易是有效的，但就灌溉而言则不然，这意味着干旱、灌溉密集型省份往往向湿润、灌溉密集型省份出口。重要的是，当纳入外国进口时，中国的大豆贸易从一个效率低下的系统转变为一个特别高效的水资源节约系统（灌溉节水 20 亿立方米/年，总节水 41 亿立方米/年）。最后，我们确定了一些具有较高灌溉生产力提高潜力的特定省份（如内蒙古）和产品（如玉米）。
