Exploring the network structure of virtual water trade among China's cities

A virtual water trade system based on a multiregional input-output (MRIO) model has been regarded as a network with regions as nodes and virtual water flows between regions as the directional, weighted links. Therefore, exploring the network structure can provide additional insights for understanding how the virtual water trade system works. This study employs the integration of the MRIO model and the complex network theory to investigate the network structure of the virtual water system for trade among China's cities, which has not been well understood. Results show that the virtual water trade system is relatively robust to shocks (e.g., droughts) from certain cities, but it has not yet achieved optimal efficiency in virtual water distribution as the volume of virtual water exchanges among cities increases in a highly nonlinear way with the increase of their trade connections. Results also show that the virtual water network can be divided into 14 communities, each of which is constituted by strongly connected cities and shows spatial structure in virtual water transfers. Cities with higher virtual water flows play a more important role in linking upstream and downstream for virtual water exchange, and those with larger virtual water exports are more likely to transfer virtual water to others closely and quickly. With a structured, quantitative characterization of the city-level virtual water network, this study can facilitate the development of effective strategies for China's water resource management.