Spatiotemporal Evolution And Environmental Impact Of Interprovincial Transfer Of China’s Grey Water Footprint

Reducing water pollution while ensuring high-speed economic growth is one of China’s important goals for current and future sustainable development.Due to significant differences in population,economic level,industrial structure,and natural endowments across different regions in China,water pollution characteristics vary greatly.Traditional studies on changes in China’s water pollution load or water pollution prevention have focused mainly on single pollutant or single economic sector,making it difficult to provide differentiated regional strategies for alleviating water pollution in China.In addition,most of the current studies related to regional water pollution analyze the impact of human activities within the regional boundary,and there are fewer analyses on the environmental impact of water pollution discharge and transfer in other regions caused by local final consumption.However,studies in other environmental fields have shown that the transfer of pollution emissions embodied in trade not only directly affect regional environmental quality,but also indirectly leads to environmental inequality among regions.Therefore,there is an urgent need to provide region-specific strategies and suggestions for regional water pollution mitigation and inter-regional equitable and sustainable development,taking into account the environmental background,resource endowment,and pollutant discharges from all production and living sectors,combined with the implied water pollutant discharge and transfer in trade.Grey water footprint（GWF）,as a water pollution assessment indicator,can effectively be used to analyze and solve the above issues.This study comprehensively considers the water pollution load of the agricultural,industrial,and residential sectors,evaluates the GWF and water pollution level（WPL）changes of four pollutants,chemical oxygen demand（COD）,ammonia nitrogen（NH₃-N）,total nitrogen（TN）,and total phosphorus（TP）,in 31provinces in mainland China.Through the environmental extended multi-regional input-output model,the GWF transfer embodied in inter-regional trade and its regional water pollution impact are analyzed,and an environmental inequality index is constructed to evaluate the regional environmental inequality caused by the hidden grey water footprint transfers in trade.Future strategies for alleviating China’s GWF are explored from the consumption side,production side,and terminal treatment side areas.The main work and conclusions of this study are as follows:Firstly,this study calculated the water pollution load of agriculture,industry,and residential sectors within the administrative boundaries of each province in China,analyzed the actual GWF and WPL of each province from 2003 to 2020,and further explored the driving force of GWF change and the spatio-temporal succession of primary water pollutant（PWP）in water body.The results showed that from 2003 to2020,China’s GWF decreased by 26.5%,and the WPL decreased from 1.09 in 2003 to0.69 in 2020.Spatially,the GWF showed a distribution pattern of high in the southeast and low in the northwest,while the WPL was relatively high in North China.The PWP changed from TP in 2007 to NH₃-N in 2008 and then to TN,and the number of provinces with TN as the PWP increased year by year,reaching 28 in 2020.The driving force analysis results showed that population effect and economic effect promoted the increase of GWF,while water use efficiency effect,technical effect,and industrial structure effect promoted the decrease of GWF.In addition,the correlation analysis with the actual surface water quality grade showed that the calculated GWF and WPL in this study can accurately reflect the actual changes in China’s surface water quality.Secondly,based on the environmental extended multi-regional input-output model,this study estimated the virtual GWF（GWF based on final consumption）of each province in China from 2007 to 2017 and the GWF transfer in regional trade.Combined with the actual GWF and WPL of each province,the impact of trade-induced GWF transfer on regional WPL was analyzed.The results showed that Beijing-Tianjin,the East Coast region,and the South Coast region were the main net exporters of GWF,and the GWF of Beijing-Tianjin mainly flowed into the Northeast,Central,and Southwest regions,while the GWF of the South Coast region mainly flowed into the Central and Southwest regions.The major provinces affected by the transfer of GWF embodied in trade were the megacity such as Beijing,Tianjin,and Shanghai,as well as provinces with the WPL near 1.Due to the fact that the GWF of these megacities mainly comes from residential and the tertiary industries,their potential to reduce local WPL through trade has been decreasing year by year.Thirdly,based on the balanced relationship between trade-related GWF and value-added transfer,this study constructs an environmental inequality index and analyzes the environmental inequality among provinces in China caused by trade from 2007 to2017.The results showed that the inter-provincial environmental inequality caused by the transfer of GWF sharply increased from 2007 to 2012,with developed provinces such as Beijing,Tianjin,Shanghai,Jiangsu,Zhejiang,Fujian,and Guangdong outsourcing their GWF while receiving additional income from 70.8%to 100%of less developed provinces.From 2012 to 2017,this environmental inequality was somewhat improved,with the proportion of provinces such as Beijing,Tianjin,Shanghai,and Jiangsu showing extra-earning status when trading with less developed provinces decreasing by 12.5%-58.3%.Although absolute environmental equality in trade is difficult to achieve,developed regions should provide more extra-payment to less developed regions and bear the corresponding consumer responsibility.Fourthly,based on GWF assessment and scenario simulation,this study predicts the changes of WPL in China from 2021 to 2035 under the baseline scenario,current policy scenario,and technical improvement scenario.And analyzes the effects of measures involved in the current policy and technical improvement scenarios on GWF from the consumption side,production side,and terminal treatment side areas.The results showed that under the baseline scenario,only the GWF of NH₃-N in China can be reduced by 0.4%,while the GWF of the other three pollutants will increase by 3.2%to 17.6%.Under the current policy scenario,the measures involved in the current policy can reduce the GWF of these four pollutants by 15.0%to 39.9%,but the GWF of eight provinces will still increase.Under the technical improvement scenario,by improving and adding measures in the production and terminal treatment sides,the GWF of the four pollutants mentioned above will decrease by 54.9%to 71.1%,and the GWF of 31provinces can be reduced.The results of this study can help to improve existing policies for different pollutants and provide regional pollution load relief strategies,and can also provide policy evaluation references for other environmental fields or emerging economies.In conclusion,by evaluating the GWF of all human activities within the administrative boundaries of each province in China,as well as the GWF based on final consumption in each province,this study analyzes the actual changes of WPL in each province,the impact of GWF transfers embodied in trade on regional WPL,and the regional environmental inequality caused by the transfer of GWF.From the perspectives of consumption,production,and terminal treatment,this study analyzes the future changes in China’s GWF and WPL,and provides decision support with industry specificity and regional differentiation for the alleviation of China’s future GWF and reduction in WPL.Additionally,this study addresses the previous lack of environmental impact research on the transfer of water pollutant discharge in interprovincial trade in previous studies,and provides a new evaluation method for quantifying regional environmental inequality in trade.