Assessing water-energy-related use system towards the targets SDG 6 and SDG7: A dynamic parallel-series DEA model

Water and energy are key elements to accomplish the Sustainable Development Goals (SDGs) of human society. The aim of this study is to acknowledge and enhance the efficiency of water-energy-related use (WERU) systems from a sustainable perspective. This paper proposes a dynamic parallel-series data envelopment analysis model to assess WERU efficiency towards the targets SDG 6 and SDG 7. The WERU system with parallel-series structure consists of water supply (WS), water use (WU), energy supply (ES), and energy use (EU) subsystems. To investigating the role of digital economy in enhancing WERU efficiency in 30 provinces of China from 2011 to 2020, the intermediary effect model and the spatial Durbin model are applied to explore the transmission mechanism and spatial spillover effect. The main findings are as follows: (1) The average overall efficiency of the WERU system is 0.60, primarily due to the suboptimal performance of the WU and EU subsystems. (2) The central region has lower efficiency scores in the WU and EU subsystems than the eastern and western regions. (3) The digital economy indirectly boosts WERU efficiency by stimulating provincial innovation and industrial structure upgrading. The digital economy is beneficial to enhancing WERU efficiency in local and neighboring provinces. This study advocates for the sustainable advancement of the WERU system by encouraging provincial innovation, upgrading industrial structures, and underscoring the growth of the digital economy.