Water footprint (WF) measures human appropriation of water resources for consumptive use of surface and ground water (blue WF) and soil water (green WF) and for assimilating polluted water (grey WF). Questions have been often asked about the exact meaning behind the numbers from WF accounting. However, to date environmental sustainability of WF has never been assessed at the sub-national level over time. This study evaluated the environmental sustainability of blue, green and grey WF for China's 31 mainland provinces in 2002, 2007 and 2012, and identified the unsustainable hotspots. Overall, the total WF increased by 30% between 2002 and 2012. The growth can be attributed to the increase of grey WF because the green and blue WF showed only a slight rise. Among all provinces investigated in 2012, eleven showed unsustainable blue WF (sustainability index SI<0), which were mainly located in the North China Plain. There were 12 provinces that displayed unsustainable green WF, and they were distributed in China's southern and southeastern areas. The grey WF was not sustainable in approximately two third of provinces (19), which were mainly located in China's middle and northern regions and Guangdong province. More than half of China's provinces showed trends of improved SI of green and blue WF from 2002 to 2012. However, the SI of grey WF decreased in almost two third of provinces. Poor levels of WF sustainability were due to water scarcity and pollution, which intensify the degradation of local rivers and ecosystems and make restoration more difficult. The results shed light on the policy making needed to improve sustainable water management, and ecological restoration of hotspot regions.
- Green water Blue water Grey water Sustainable development Ecological restoration