水资源安全是保障地区可持续发展的关键基础之一。虚拟水是产品和服务在贸易转移的过程中蕴含的水资源，为水资源安全研究提供了新思路。我国西北地区（以下简称“西北地区”）气候干旱，生态脆弱，社会经济发展对水资源的依赖程度高。同时，作为我国重要的粮食生产地和矿产贮藏地，西北地区面临水土资源配置失调、水资源开发利用压力高等问题，水资源安全存在隐患。开展西北地区近远程虚拟水流动格局演变及影响因素研究，对促进西北地区的协调发展、水资源节约利用具有重要意义。

近年来，近远程耦合成为水资源要素研究的热点。将近远程耦合的思想应用于虚拟水贸易研究中，能够较好阐述地区对内、外部水资源的依赖性。已有的西北地区虚拟水研究关注远程虚拟水贸易，对比分析西北地区虚拟水近远程流动的研究较少。由于投入产出表数据获取的限制，已有研究大多为单一年份或者两年对比分析，随着西北地区经济迅速发展，有必要对西北地区近远程虚拟水流动开展全产业、长时间的研究。

本文通过环境拓展投入产出模型，从近远程视角对西北地区2007-2017年省际虚拟水流动情况进行研究。首先，通过对比分析西北地区近远程虚拟水特征时空演变，研究西北地区虚拟水的内外部依赖程度；其次，利用空间分析方法探讨近远程虚拟水流动空间格局演变，具体来说，运用标准差椭圆分析近远程虚拟水流动方向变化，运用空间自相关分析方法研究虚拟水流动空间聚集特征。最后，运用结构分解分析方法，研究技术效应、结构效应、经济效应、人口效应和需求效应对西北地区虚拟水近远程流动的影响。研究结果表明：

（1）西北五省区对内外部虚拟水依赖程度空间差异较大。陕西虚拟水主要依赖远程流入，研究期内接收远程流出虚拟水为14.8-61.1亿m3，缓解了本地水资源压力。其他省区虚拟水主要依靠本地供应。研究期内，新疆和甘肃还供应远程流出虚拟水199.2-288.6亿m3和16.1-52.6亿m3。

（2）西北地区的虚拟水近程流动趋于活跃，近程流出以新疆流向其他四省区为主，近程流入逐渐形成以陕西为主要流入地的格局。西北地区的近程虚拟水流入（出）量从2007年的20.09亿m3增至2017年的40.4亿m3，表明有越来越多的商品和服务在西北五省区之间流通。西北地区近程流出的方向性显著减弱，新疆的虚拟水近程流出在西北地区的占比从2007年的73.4%下降至2017年的51.8%，近程流出标准差椭圆重心逐渐远离新疆、向东南方向移动，表明西北地区其他四省区的虚拟水近程流动的参与度逐渐提高。

（3）西北地区的远程虚拟水流动以净流出为主。在研究期内，华东和中南地区始终为西北地区远程流出和远程流入第一和第二多的两大地区，远程流出分别为113.26-179.91亿m3和53.53-122.44亿m3，远程流入分别为29.03-52.94亿m3和25.03-34.20亿m3，西北地区虚拟水远程流出和净流出的热点集中于华东和中南地区的部分省份。随时间变化，西北地区与西南地区的虚拟水远程流出趋于增加，远程流出标准差椭圆重心呈现向西南方向转移的趋势；西北地区接收来自东北地区的虚拟水远程流入逐渐增加，远程流入标准差椭圆重心呈现向东北方向转移的趋势。

（4）西北地区近远程虚拟水流动主要受技术和经济的影响。技术效应为主要的负向影响，经济效应为主要的正向影响，人口效应是轻微的正向影响，结构和需求效应以正向为主，虚拟水流动与距离关系不大。对于西北地区远程虚拟水流入，经济效应的绝对值略大于技术效应的绝对值；对于西北地区虚拟水近程流动和远程虚拟水流出，技术效应的绝对值更大，可以抵消经济效应带来的虚拟水增加。

Water resources security is the key to ensure regional sustainable development. Virtual water trade is the process of water resources transferring between countries or regions through product and service trade. Virtual water trade provides a new idea for the research of water resources security. Northwest China has a dry climate and fragile ecology. The economic and social development highly depends on water resources in Northwest China. At the same time, as an important reserve base for grain production and the main storage of mineral resources in China, Northwest China is facing the problems, which are unbalanced allocation between water and soil resources, high utilization rate of water resources, and so on. There are hidden dangers in water resources security in Northwest China. This study the evolution of inter-provincial virtual water flow patterns and its driving factors of in Northwest China. It is of great significance to promote the coordinated development and intensive utilization of water resources in Northwest China.

In recent years, local and distant coupling has become the hotspot of resource elements research. Appling local and distant coupling to virtual water trade can explain the dependence on internal or external water resources. The existing studies on Northwest China’s virtual water pay attention to distant virtual water trade, and there are few studies on comparative analysis of local and distant virtual water flow in Northwest China. Due to the timing limitation of input-output table, most existing studies are in a single year or comparative analysis of two years. With the rapid economic development, it is necessary to carry out industries and long-term study on inter-provincial virtual water flow in Northwest China.

This study focuses on the inter-provincial virtual water flow through the environmental expansion Input-Output model from 2007 to 2017 in Northwest China. Firstly, this study compared the temporal and spatial evolution of local and distant virtual water flow in Northwest China and analyzed the internal and external dependence of virtual water in Northwest China. Secondly, this study used the spatial analysis method to explore the pattern evolution of local and distant virtual water flow. Specifically, the standard deviation ellipse is used to analyze the change of local and distant virtual water flow direction, and the spatial autocorrelation analysis method is used to study the spatial aggregation characteristics of virtual water flow. Finally, this study uses structural decomposition analysis to analyze the impact of technology effect, structure effect, economic effect, population effect and demand effect on the local and distant virtual water flow in Northwest China. The results shows:

(1) The five provinces have great spatial differences in their dependence on internal and external virtual water in Northwest China. Shaanxi’s virtual water mainly relies on remote inflow, and the virtual water received from distant outflow during the study period is 1.48-6.11 billion m3. Virtual water in other provinces mainly depends on local supply. During the study period, Xinjiang and Gansu also supplied 19.92-28.86 billion m3 and 1.61-5.26 billion m3 of distant outflow.

(2) The local virtual water flow tends to be active in Northwest China. The local outflow mainly flows from Xinjiang to the other four provinces, and the local inflow gradually forms a pattern with Shaanxi as the main inflow place. The inflow (outflow) of short-range virtual water flow in Northwest China increased from 2.009 billion m3 in 2007 to 4.04 billion m3 in 2017. It shows that more and more goods and services are circulating among the five provinces in Northwest China. The directionality of local outflow in Northwest China is significantly weakened. The proportion of virtual water local outflow decreased from 73.4% in 2007 to 51.8% in 2017 in Northwest China. The standard deviation elliptical center of local outflow gradually moves away from Xinjiang and to the Gansu. It indicates that the participation of virtual water local flow in other four provinces in Northwest China is gradually increasing.

(3) The distant virtual flow in Northwest China is dominated by net outflow. During the study period, East China and Central South China have always been the two regions with the largest and second largest distant outflow and distant inflow in Northwest China. The hotspots of distant outflow and net outflow of virtual water are concentrated in some provinces in East China and Central South China. The distant outflow to southwest regions tends to increase. The standard deviation elliptical center of distant outflow tends to the southwest. The virtual water from the northeast region gradually increases. The standard deviation elliptical center of distant inflow shows a trend to the northeast.

(4) The local and distant virtual water flow is mainly affected by technology and economy in Northwest China. Technology effect is the main negative impact and economic effect is the main positive impact. Population effect is a slight positive impact. Structure and demand effect are mainly positive. The virtual water flow has little relationship with distance in Northwest China. For the distant virtual water inflow in Northwest China, the absolute value of economic effect is slightly greater than that of technical effect. For the local flow and distant outflow in Northwest China, the absolute value of technical effect is greater, which offsets the increase of virtual water caused by economic effect.