How industrial water resources green efficiency varies in China: a case study of the Yangtze River Economic Belt considering unexpected output

Strengthening the protection and utilization of water resources is very important for the development of the Yangtze River Economic Belt (YREB). The YREB spans the three regions of the East, Middle and West of China, which is not only the inland river economic belt with the largest economic aggregate in China, but also the leading demonstration belt for the construction of ecological civilization. This paper uses the minimum distance to the strong frontier (mSBM) model to evaluate the industrial water resources green efficiency (IWRGE) in the YREB from 2000 to 2018, taking the industrial gray water footprint as bad output, which can more accurately measure the water efficiency of the current industrial sector. Then, compared with the traditional industrial water resources utilization efficiency (IWRUE), the temporal and spatial differences and influencing factors of the IWRGE are further analyzed. The results are as follows: First, the IWRUE in the YREB has been improved to a certain extent in the sample period, and there are obvious differences in provinces. The IWRUE of economically developed provinces is higher than economically underdeveloped provinces. Second, the IWRGE after adding industrial gray water footprint is lower than the IWRUE in the YREB, indicating that the IWRUE without considering the cost of water ecological damage is "false high". Third, the IWRGE in the upper, middle and lower reaches of the YREB shows a "U" type change trend of "decreasing first and then rising". Fourth, the IWRGE in the YREB shows an obvious spatial distribution pattern of "both ends high and intermediate low". The pressure to save industrial water and reduce pollution is especially intense in the middle reaches. Finally, economic growth, property right structure, and opening up can significantly promote the IWRGE, while water endowment, water structure, technological progress, and environmental regulation significantly inhibit the improvement of the IWRGE.