Direct and embodied energy-water-carbon nexus at an inter-regional scale

Energy, water and carbon flows are highly intertwined in economy and influence urban and regional sustainability. Few insights have been acquired for energy-water-carbon nexus at inter-regional scale considering both in- and trans-boundary flows. Here we propose an interactive framework to assess inter-regional energy-water-carbon nexus, encapsulating both direct nexus flows within territory and nexus flows embodied in final consumption. An inter-regional input-output model is established to account for energy-related water footprint, water-related energy footprint and water-related carbon footprint from a consumption-based perspective. Using Guangdong-Hong Kong as a case study, we find that though these nexus footprints contribute a small fraction of the total energy, water and carbon footprints of both regions in 2012, their impacts should not be neglected due to higher intensities. The direct intensities of water-related energy and water-related carbon are more than 2 times higher than the total energy and carbon intensities, while their embodied intensities are over 6 times higher. Inter-regional trade plays an important role in controlling energy-water-carbon nexus of both sides. About 29-44% of the consumption-based nexus footprints of Hong Kong's consumption are outsourced to Guangdong and other regions, while 21-24% of Guangdong's footprints are from production elsewhere. These are strong signals showing the importance of managing energy-water-carbon nexus on a cross-border and fully-interactive basis.