Exploring absolute sustainability-informed water inequality indicators of Chinese city clusters

Within a city cluster, central cities rely on imports of water-intensive products from hinterland cities to avoid exceeding domestic planetary boundaries (PB). Yet, the role of PB-informed virtual water trade in redistributing scarce freshwater resources among and within city clusters remains underexplored. This study addresses this gap by analysing city cluster-level PB-exceeded and PB-surplus water footprints of 313 Chinese cities. The water exceedance footprint measures the exceeded amount of water withdrawn against local water PBs to meet the demand of a city. The surplus water footprint quantifies the surplus water available within local PBs that can be sustainably utilized to meet the demand of a city. By employing a Chinese city cluster-level multi-regional input output model, we identified to what extent are city cluster demands for goods and services driving PB transgression. In 2017, Chinese city water exceedance footprint (WEF) amounts to 48.8 km³, while the surplus water footprint (SWF) is almost three times than WEF, reaching 136.7 km³. Net WEF flows primarily from central to the non-central cities, while the net SWF flows in the opposite direction. This suggests central cities could shift from WEF exporters to SWF importers. Across the top five city clusters, net import flows of both PB-exceedance and surplus water are concentrated in the Yangtze River Delta. Contrary to prior research, city cluster-level virtual water trade is not strictly governed by geographical distance, nor do wealthier cities consistently show lower emission to value-added ratios compared to poorer ones. Our revised virtual water trade analysis advance knowledge on how city cluster consumption is transgressing water PBs.