Understanding the two-way virtual water transfer in urban agglomeration: A new perspective from spillover-feedback effects

Interregional trade not only contributes to economic growth but also causes a large amount of virtual water transfer. The virtual water transfer brings about two-way impact of environmental stress between regions. It is essential to examine the two-way impact mechanism to achieve water sustainability. Interregional virtual water transfer includes three aspects of effects: multiplier, spillover and feedback effects. Among them, multiplier effect is the interaction in a single region. Spillover effect generally refers to the one-way impact of former region's economic development on latter region, while the feedback effect refers to the economic change of latter region in turn has an impact on the former region on the basis of the spillover effect. However, most studies have been focusing only on the one-way impact of virtual water transfer, which are the multiplier and spillover effects. This paper introduces a new spillover-feedback effects model to measure the two-way impact of virtual water transfer in urban agglomerations, and takes the Beijing, Tianjin and Hebei capital agglomerations in China as a specific case. The results illustrate that the spillover-feedback effects had significant contributions to virtual water transfer. From the perspective of regional scale, Beijing was a net importer of virtual water, with a net import volume of 1.019 × 10⁸ m³. Tianjin and Hebei were net exporters of virtual water, with net exports of 0.069 × 10⁸ m³ and 0.950 × 10⁸ m³ respectively. The values of the feedback effect were large and should not be ignored, which accounted for up to 40% of the spillover effect. Furthermore, at the sectoral scale, the sectors with large ratios of spillover-feedback effects to total effects in regions included mining, agriculture, manufacturing and transportation. In Beijing, this ratio of mining exceeded 50%. Additionally, the effect intensity patterns were different from the effect patterns, which prove that the regional ability to stimulate water consumption was not consistent with the actual impacts. Finally, regions should pay more attention to managing the industries and enterprises with high virtual water export, adjust the trade structure, strengthen inter-regional cooperation and clarify regional responsibilities for water-saving. In a word, understanding interregional two-way impact mechanism is essential for the sustainable and collaborative development of the economy and environment in urban agglomerations.