Virtual scarce water in China

Investigating agricultural water sustainability in arid regions with Bayesian network and water footprint theories

Water scarcity is a significant constraint in agricultural ecosystems of arid regions, necessitating sustainable development of agricultural water resources. This study innovatively combines Bayesian theory and Water Footprint (WF) to construct a Bayesian Network (BN). Water quantity and quality data were evaluated comprehensively by WF in agricultural production. This evaluation integrates WF and local water resources to establish a sustainability assessment framework. Selected nodes are incorporated into a BN and continuously updated through structural and parameter learning, resulting in a robust model. Results reveal a nearly threefold increase of WF in the arid regions of Northwest China from 1989 to 2019, averaging 189.95 × 108 m3 annually. The region's agricultural scale is expanding, and economic development is rapid, but the unsustainability of agricultural water use is increasing. Blue WF predominates in this region, with cotton having the highest WF among crops. The BN indicates a 70.1 % probability of unsustainable water use. Sensitivity analysis identifies anthropogenic factors as primary drivers influencing water resource sustainability. Scenario analysis underscores the need to reduce WF production and increase agricultural water supply for sustainable development in arid regions. Proposed strategies include improving irrigation methods, implementing integrated water-fertilizer management, and selecting drought-resistant, economically viable crops to optimize crop planting structures and enhance water use efficiency in current agricultural practices in arid regions. This study not only offers insights into water management in arid regions but also provides practical guidance for similar agricultural contexts. The BN model serves as a flexible tool for informed decision-making in dynamic environments.

Assessing the ecological security of the Three Gorges reservoir complex ecosystem based on the improved three-dimensional emergy ecological footprint model

The ecological security (ES) of the reservoir complex ecosystem (RCE) is one of the critical components of watershed water security and sustainable development. Hence, accurately assessing the ES of the RCE is of utmost importance. This study proposed a novel ecological security assessment model based on the improved three-dimensional emergy ecological footprint (ESM-IEEF3D), which integrated various emergy flows during the RCE's construction and operation into a three-dimensional emergy ecological footprint (EEF3D) calculation account. The Three Gorges Project (TGP) is selected as a case study to evaluate the ES from 1993 to 2022 comprehensively. The results showed that the Three Gorges RCE mainly showed an ecological remainder state, and the inflow runoff enormously promoted the TGP's sustainability. The EEF3D indicated a fluctuation decrease trend with a mean value of 7.18 × 102 ha, illustrating that TGP's ecological security and sustainability levels are gradually improving. Regarding the ES evaluation indicators, the TGP's resource dependency and ecological pressure on the natural ecosystem and the external socio-economic system are steadily relieved. Furthermore, the Three Gorges RCE's resource utilization condition is safe, the structural characteristics are healthy, and the eco-economic coordination degree is continuously enlightening. Finally, applicable policy implications for improving the ecological security of Three Gorges RCE were provided. This study helps to understand the complex relationship between humans and ecosystems. It provides a novel framework to be used as an evaluation index and policy insights for hydropower ecological security and sustainable development.

Exploring China's water scarcity incorporating surface water quality and multiple existing solutions

Water scarcity has threatened the sustainability of human life, ecosystem evolution, and socio-economic development. However, previous studies have often lacked a comprehensive consideration of the impact of water quality and existing solutions, such as inter-basin water transfer and unconventional water resources, on water scarcity. In this paper, an improved approach was proposed to quantify water scarcity levels by comprehensively considering surface water quality and multiple solutions. China's water scarcity was first assessed at a high spatial resolution on a monthly basis over the 5-year period from 2014 to 2018. Then, the driving factors including water quality and solutions were identified by a geographic detector model. Finally, an in-depth investigation was conducted to unravel the effects of water quantity solutions (i.e., inter-basin water transfer and unconventional water use), and water quality solutions (i.e., improving surface water quality) on alleviating water scarcity. Based on monthly assessments considering water quality and multiple existing solutions, the results showed that over half of the national population (∼777 million) faced water scarcity for at least one month of the year. Agricultural water use and inadequate water quality were the main driving factors responsible for China's water scarcity. Over four-fifths of the national population (∼1.10 billion) could benefit from alleviated water scarcity through a combination of water quantity and quality solutions. However, the existing solutions considered were insufficient to completely resolve water scarcity in China, especially in Northern China, persisting as a challenging issue. The results obtained from this study provided a better understanding of China's water scarcity, which could contribute to guiding future efforts aimed at alleviating water scarcity and ensuring water security in China.

Economic risks hidden in local water pollution and global markets: A retrospective analysis (1995-2010) and future perspectives on sustainable development goal 6

Pollution from untreated wastewater discharges depletes clean water supply for humans and the environment. It poses adverse economic impacts by determining agricultural yields, manufacturing productivity, and ecosystem functionality. Current studies mainly focus on quantity-related water scarcity assessment. It is unknown how low water quality amplifies local water stress and induces cascading economic risks globally. In this study, we estimated both quality and quantity-related water scarcity index (WSI), local economic water scarcity risk (WSR), and cascading virtual WSR evident in global trade markets across 40 major economies from 1995 to 2010. We find developing countries, e.g., India and China, witnessed fast growth in both quantity and quality-related WSI. Major developed economies, e.g., the US and Germany, experienced a modest increase in water stress but alleviated quality-related risks. Local economic risk (WSR) grew from $116B to $380B, with quality-related risks rising from 20 % to 30 %. Virtual economic WSR in global supply chains increased from $39B to $160B, with quality-related risks increasing from 19 % to 27 %. China became the top exporter of economic WSR, ranked above the US, France, and Japan, and the second-largest position as an importer, trailing only the US. We finally conducted scenario modeling by 2030, assuming different progresses on SDG 6 targets. The findings suggest that only the most ambitious progress in both water quality enhancement and efficiency improvement helps to alleviate ∼20 % economic WSR globally. Our findings underscore the necessity for strategies that integrate management of untreated wastewater flows, improved water use efficiency, and diversification of supply chain networks to enhance global economic resilience to water challenges in the future.

Advanced oxidation of recalcitrant chromophores in full-scale MBR effluent for non-potable reuse of leachate co-treated municipal wastewater

Wastewater non-potable reuse involves further processing of secondary effluent to a quality level acceptable for reuse and is a promising solution to combating water scarcity. Recalcitrant chromophores in landfill leachate challenge the water quality for non-potable reuse when leachate is co-treated with municipal wastewater. In this study, we first use multivariate statistical analysis to reveal that leachate is an important source (with a Pearson's coefficient of 0.82) of recalcitrant chromophores in the full-scale membrane bioreactor (MBR) effluent. We then evaluate the removal efficacies of chromophores by chlorination, breakpoint chlorination, and the chlorination-UV/chlorine advanced oxidation treatment. Conventional chlorination and breakpoint chlorination only partially remove chromophores, leaving a colour level exceeding the standards for non-potable reuse (>20 Hazen units). We demonstrate that pre-chlorination (with an initial chlorine dosing of 20 mg/L as Cl2) followed by UV radiation (with a UV fluence of 500 mJ/cm2) effectively degraded recalcitrant chromophores (>90%). By quantifying the electron donating capacity (EDC) and radical scavenging capacity (RSC) of the reclaimed water, we demonstrate that pre-chlorination reduces EDC and RSC by up to 64%, increases UV transmittance by 32%, and increases radical yields from UV photolysis of chlorine by 1.7-2.2 times. The findings advance fundamental understanding of the alteration of dissolved coloured substances by (photo)chlorination treatment and provide implications for applying advanced oxidation processes in treating wastewater effluents towards sustainable non-potable reuse.

Physical and virtual water transfers in China and their implication for water planetary boundary

China is an extremely water-scarce country with an uneven distribution of regional water resources. We define two absolute sustainability indicators, using the multi-regional input‒output (MRIO) model to outline the contribution of China's physical and virtual water transfers in mitigating the problem of regional water boundary-exceeding. Although the overall use of freshwater resources is within the safe operation space, 55% of province's water resource development transgresses the local water planetary boundary. Physical and virtual water transfers effectively mitigate the stress of water supply to the water planetary boundary in China's water-scarce regions. Among them, the role of virtual water transfers occupies the main part. The cost of using physical water in water-receiving regions and the situation of virtual water flowing from water-scarce regions to developed water-rich regions cannot be ignored, and a small number of provinces are responsible for most of the virtual water net imports and exports. The obtained results are helpful for the redistribution of water planetary boundary transgressing responsibilities among provinces and the formulation of absolute sustainable water resources management policies.

Exploring the drivers of quantity- and quality-related water scarcity due to trade for each province in China

Previous studies have explored virtual water flows due to interprovincial trade within China as well as related impacts on both regional quantity- and quality-related water scarcity aspects. However, the driving forces behind changes in these impacts remain unknown, especially the quality-related water scarcity. Exploring these driving forces can provide targeted measures to mitigate the negative impact of trade on these two types of water scarcity issues. In this study, blue and grey water footprints have been calculated under the consideration of interregional trade between provinces within China and those attributed to international exports from 2007 to 2015. This calculation was based on multi-regional input output model (MRIO). Moreover, the drivers of changes in blue and grey water footprints due to trade have been explored through structural decomposition analysis. The results showed that blue and grey water footprint increased and then slightly decreased from 2007 to 2015 in China. At the same time, interregional trade made an increasing contribution to the blue and grey water footprint, and the proportion increased from 28.8% to 35.0% and from 22.4% to 28.6%, respectively, from 2007 to 2015. The roles of importers and exporters regarding the blue and grey water footprint driven by interprovincial trade within China have changed little, and the quantity- and quality-related water scarcity issues of the main exporters have been intensified by interprovincial trade. A reduction in the water footprint intensity yielded the largest contribution to curb the increase in blue and grey water footprint driven by interprovincial trade. Our study showed that an improvement in efficiency of water use from both quantity and quality perspectives is the key to accomplish sustainable water use in China, especially considering the impact of trade on regional quantity- and quality-related water scarcity issues.

Imbalance in the city-level crop water footprint aggravated regional inequality in China

Crop production is the main consumer of water resources. The heterogeneous water resource endowments and imbalanced crop water use exacerbate regional resource consumption inequality. In this study, we quantified the crop water footprint (CWF) of 356 cities in China from 2000 to 2020, measured the inequality between the city CWF and water resources, and identified different strategies to alleviate regional CWF inequality. We found that the average CWF from 2000 to 2020 varied widely across cities, ranging from 0.03 × 10⁸ m³ to 806.78 × 10⁸ m³, and the inequality between city CWF and local water resource endowment was increasing. China had a strong dependence on green water in crop production, and its proportion increased from 52.48 % to 67.17 %. The Gini coefficient of the green water footprint increased from 0.545 to 0.621, and the degree of inequality increased significantly. In addition, the blue water and gray water continuously showed great inequality, especially the blue water, the Gini coefficient of which was 0.724 in 2020. The results show significant disparities in CWF among cities, which have highly exacerbated regional inequality in China. Improving the utilization rate of green water is an important measure to balance the allocation between serving the natural ecosystem and meeting the basic human needs. This study revealed for the first time the inequality of city-level CWF and highlights the severe situation of inequality among regions in China. Balancing the inequality between CWF and water resource endowment at city-level is conducive to fundamentally solving the problem of unreasonable water resource allocation.

Telecoupling China's City-Level Water Withdrawal with Distant Consumption

Trade causes the geospatial separation of production and consumption, which drives telecoupling between resource utilization and distant consumption. While benefiting the economy, trade can also exacerbate resource use inequality among regions. Here, we propose telecoupled water withdrawal (TWW) to examine the impact of distant consumption on local water resources, defined as local water withdrawal driven remotely by consumption in other regions. We characterize the TWW in China in 2015 at the city level (350 cities) using a nested multiregional input-output model. We find that approximately 20% of TWW is linked to foreign consumption, more than a quarter of which is driven by the United States. Moreover, cities with high TWW are concentrated on the Southeast coast and in Northwest China. Cities in Xinjiang province (Northwest China) account for 12% of the national TWW but only 0.7% of China's GDP. Our findings shed light on the telecoupling of pressure on local water resources in China cities and distant consumption at the global scale, calling for joint efforts by the contributors and beneficiaries of TWW to ensure the synergistic sustainability of water resources and trade.

Consumption-based emissions at city level in China and the spatial heterogeneity analysis of the influential factors

It is of great significance to identify the critical influential factors of pollutant emissions for emission mitigation. However, city disparity implies different priorities for regional mitigation. This study aims to estimate the consumption-based emissions of 309 prefecture-level cities in China based on the multi-region input-output table and the sectoral NOx emission inventory and investigate the emission transfer phenomenon among cities and sectors. In addition, a geographically weighted regression method is used to analyze the spatial heterogeneity in the driving factors of regional consumption-based emissions. The results reveal that the top 10 cities in consumption-based emissions account for 25.2% of emissions and contribute 22.6% to GDP. The consumption-based emissions are mainly driven by local demand (72.79%) at the regional level and by construction activities (94.43%) at the sectoral level. Besides, the results also show the spatial variances in contributions of driving forces to consumption-based emissions. Economic growth has been identified as the most important factor which promotes consumption-based emissions. However, disposable personal income, per capita road area, urbanization, and percentage of tertiary industry GDP are conducive to reduce consumption-based emissions in some cities of China. It could be concluded that policies without consideration of the emissions from a consumption perspective are difficult to achieve effective emission reduction.

Life cycle assessment of shared electric bicycle on greenhouse gas emissions in China

Following the bike-sharing system, the shared electric bicycle (SEB) is experiencing explosive growth in China as an emerging shared transportation mode. While shared transportation has long been linked to energy conservation and reducing emissions, a major problem facing SEB is whether it can reach the goal of greenhouse gas (GHG) reduction. This paper aims to evaluate GHG emissions at each stage of production, operation, and disposal of the SEB using life cycle assessment of GHG emissions. We also compared the differences in GHG emissions between the recycling incineration scenario (H1) and the recycling degradation scenario (H2) in the disposal stage. The GHG emissions of SEB in the production and operation stages were found to be 379.6173 kg CO₂-eq and 183.4663 kg CO₂-eq, respectively. However, the GHG emission reduction in the use stage was 1049.8374 kg CO₂-eq. Thus, the net GHG reduction in the life cycle of the SEB was 487.3923 kg CO₂-eq. (H1) and 433.9215 kg CO₂-eq. (H2), respectively, indicating that SEB had a green effect. Non-recyclable parts of SEB will take 48 years to degrade in landfills in the H2 scenario. The GHG emission thresholds for SEB were further discussed. When the average daily turnover rate of SEB was less than 4 and its operation day was less than 479, SEB would not be able to achieve the goal of GHG reduction in the whole life cycle, with the riding statistics remaining unchanged. Finally, some advice for practical issues of electric bicycle sharing in energy conservation and GHG reduction were presented in response to the results.

Water transfer infrastructure buffers water scarcity risks to supply chains

Inter-basin water transfer (IBWT) infrastructure has been expanding to deliver water across China to meet water demands in populated and industrial areas. Water scarcity may threaten the ability to produce and distribute goods through supply chains. Yet, it is not clear if IBWTs transmit or buffer water scarcity throughout supply chains. Here we combine a national database of IBWT projects and multi-region input-output analysis to trace water transferred by IBWT and virtual scarce water (scarcity weighted water use) from IBWT sourcing basins to production sites then to end consumers. The results indicate that production and final consumption of sectoral products have been increasingly supported by IBWT infrastructure, with physically transferred water volumes doubling between 2007 and 2017. Virtual scarce water is about half of the virtual water supporting the supply chain of the nation. IBWT effectively reduced virtual scarce water supporting the supply chains of most provinces, with the exposure to water scarcity reduced by a maximum of 56.7% and 15.0% for production and final consumption, respectively. IBWT Infrastructure development can thus buffer water scarcity risk to the supply chain and should be considered in water management and sustainable development policy decisions.

Water footprint of nations amplified by scarcity in the Belt and Road Initiative

The growing water scarcity due to international trade poses a serious threat to global sustainability. Given the intensified international trade throughout the Belt and Road Initiative (BRI), this paper tracks the virtual water trade and water footprint of BRI countries in 2005-2015. By conducting a multi-model assessment, we observe a substantial increase in BRI's water footprint after taking water scarcity into account. Globally the BRI acts as a net exporter of virtual water, while the export volume experiences a decreasing trend. Noticeable transitions in nations' role (net exporters vs. net importers) are found between the BRI and global scales, but also between with and without considering water scarcity. Overall economic and population growth is major drivers of scarcity-weighted water footprint for BRI nations, as opposed to the promotion of water-use efficiency and production structure that can reduce water scarcity. Improving international trade and strengthening cooperation on water resources management deserve priority in alleviating the water scarcity of BRI.

Limited water scarcity mitigation by expanded interbasin physical and virtual water diversions with uneven economic value added in China

Interbasin water diversion projects and virtual water transfers embedded in exchanged goods and services are two effective solutions to water deficits. However, the associated real responses in water quantity and quality scarcities and the economic efficiencies remain unclear. Here, we tracked the blue water scarcities, water pollution levels, and economic value added through interbasin physical and virtual water diversions across nine river basins by sector in China from 2007 to 2015. The total national blue and grey water footprints were 365 Gm³yr^-1 and 592 Gm³ yr^-1, in which the Yangtze River basin accounts the most for 32 % and 37 %, respectively, by 2015. The physical water diversions increased by 52 % to 16.9 Gm³yr^-1. The blue virtual water transfers increased by 24 % to 176 Gm³yr^-1, whereas the grey virtual water transfers decreased by 10 % to 266 Gm³yr^-1. Agriculture related interbasin virtual water flows showed opposite directions to those driven by the industry sector. Although with uneven value added while growing, limited effects mitigated water quantity and quality stresses, especially in the drier Yellow, Northwest, and Hai River basins where the capital is located. Half of the basins had low and declining synergy scores, suggesting an urgent need to achieve synergies between resources, the environment, and the economy across basins.

Seeking sustainable pathway of crop production by optimizing planting structures and management practices from the perspective of water footprint

Water shortage threatens sustainable agriculture and food security globally. The Huanghuaihai Plain plays a critical role in ensuring China's food security, but at the expense of groundwater quantity and quality. Approaches that integrate crop production and environmental goals offer promise for achieving more sustainable water management in agriculture, yet little work has been done to link potential solutions with planting structure and resource management. The spatiotemporal variation of water footprint, water scarcity footprint, and green water occupancy rate for seven major crops, and the sustainability index and reduction potential of ten targeted reduction scenarios across 486 counties were quantitatively assessed in the Huanghuaihai Plain during 1985-2015. Total and gray water footprints dramatically increased by 59.5 % and 446.8 % from 1985 to 2015, respectively. The water scarcity footprint increased from 43.3 × 10⁹ to 49.9 × 10⁹ m³ and green water occupancy rate decreased from 37.8 % to 36.1 %. Among the single measures, reducing nitrogen input or its leaching would have the optimal reduction potential in WF_total (reduced by 5.5-11.0 %), while adjusting planting structure would have the best sustainable performance. More importantly, the areas with the greatest reduction potential in blue water footprint by deficit irrigation and adjusting planting structure were located in the southeastern and middle parts of the plain, respectively, suggesting that differentiated strategies are required for regional water sustainability. The findings provide not only integrated approaches to inform targeted water management decision making in the Huanghuaihai Plain, but also best practices that may be applicable to other regions facing similar resource concerns.

Quality matters: Pollution exacerbates water scarcity and sectoral output risks in China

Pollution exacerbates a region's water scarcity by making water unfit for different uses and reducing freshwater availability. Local water scarcity may lead to economic output losses, and the risk can be transmitted to downstream sectors through reduced input supplies. Previous studies focus on quantity-based water scarcity assessment. It is still unknown how water quality constraints may amplify economic risks of local water-use sectors and distant economies. Here we introduce an integrated method and assess the impacts of both quantity and quality-based local physical water scarcity risks (LWSR) and virtual water scarcity risks (VWSR) in domestic trade system in China. We find in 2017 quality-based LWSR and VWSR in China are ∼593 and ∼240 billion US$. Inclusion of water pollution constraints almost doubles the risks of economic losses due to insufficient clean water supply. We then identify critical regions and sectors that are highly risky or vulnerable to the supply chains. We find water pollution makes risky VWSR exporters more centralized in a few Northern provinces where available freshwater resources are already limited, e.g. the agriculture sector in Hebei province. VWSR importers span broadly, but water pollution increases concentrations of upstream suppliers that face local water scarcity for most provinces, decreasing overall resilience of China's domestic trade network. Our results underscore the needs to alleviate overall scarcity risks by conserving physical water resources and improving water quality simultaneously.

Global spatio-temporal change assessment in interregional water stress footprint in China by a high resolution MRIO model

Developing effective strategies to alleviate increasing water stress in China requires an understanding of how consumption and production drive water stress footprints (WSF) at a high resolution and multiple spatial and temporal scales. However, current Chinese multi-regional input-output (CMRIO) models have limited resolution. Here, we build a high-resolution international MRIO model covering 31 Chinese provinces, 163 sectors, to address this issue, and then analyze the impact of changes in China's interprovincial and international trade patterns on the WSF from 2012 to 2017. We find that China's water stress embodied in inter-provincial trade has increased year after year, to 5606 km³ H₂O-eq in 2017, exceeding 50 % of the total domestic footprint. Domestic water stress transfer is most apparent in the outsourcing of water stress from eastern coastal regions to Central and Western regions, with the top interregional supply chain paths mainly associated with the demand of processed rice and tobacco products. China has transformed into a net exporter of water stress in 2017, with water stress exports to developing countries accounting for 54 % of total exports, up from 51 % in 2012. With deepening globalization, trade between China and developing countries has boosted bilateral economic development, while also exacerbating water stress in China. In addition to agricultural cultivation, industrial products such as plastics and steel exported to meet international industries further contribute to water stress in Northern China. Further identify hotspots of water stress consumption is needed to prioritize actions to relieve regional water stress in a more effective manner, and our study can provide key information.

Pollution exacerbates interregional flows of virtual scarce water driven by energy demand in China

Existing studies on the virtual scarce water flows within the water-energy context focus on water quantity while largely ignoring water quality. This study improves the quantification method of scarce water uses by considering both blue water (representing water quantity) and grey water (indicating water quality). Based on a scarce-water extended multi-regional input-output model, we investigate the virtual scarce water flows driven by energy demand across 31 Chinese regions in 2012 and 2017. The results show that considering water quality provides new insights into the patterns of interregional flows of virtual scarce water driven by energy demand. The virtual integrated scarce water (VISW) flows, which consider both water quantity and quality, are 5 times the volume of virtual quantity-based scarce water (VQSW) flows. Moreover, certain regions (e.g., Hebei) are recognized as net VISW exporters, but are net importers in terms of VQSW. There are significant differences in the critical interregional pairs identified based on net VISW flows (e.g., Shandong-Zhejiang, and Shandong-Guangdong) and net VQSW flows (e.g., Heilongjiang-Guangdong, and Liaoning-Shaanxi). To reduce water scarcity based on the combined effect of both quantity and quality, the critical VISW interregional pairs should enhance cooperation through compensation payments and interregional technology transfer. This study highlights the importance of water quality in the assessment of virtual scarce water uses. Employing virtual scarce water as a policy tool to mitigate water scarcity might fail without the consideration of water quality.

How far are we from possible ideal virtual water transfer? Evidence from assessing vulnerability of global virtual water trade

With the increasing contradiction between water demand and supply in a telecoupled society where nature and human interplay intensively over distance, virtual water trade (VWT) plays an indispensable role in global water use sustainability. There has been little quantitative analysis of global water use sustainability depicting both overall system characteristics and flows between subsystems. In such a context, the extent to which virtual water transfer deviates from possible ideal expectations (i.e., virtual water flows from water-abundant regions to water-scarce ones), and its impact on global water use sustainability, are not well evaluated. Therefore, the global VWT vulnerability framework is proposed to delineate the gap between the real VWT and the possible optimal scenario, providing potential space for future optimization and regulation. Represented by the ratio of weighted total virtual water volume to the original one, the vulnerability is assessed from 2005 to 2015 based on the Eora input-output database and Virtual Water Transfer Multiplier which assigns differentiated weights to per unit volume of virtual water transfer based on the water stress levels of importers and those of exporters. Results show that the global VWT vulnerability has increased by 18.9% during the study period, with Africa and Southern and Central Asia making the biggest contribution. Developed countries contributed around 80% of the increased global VWT vulnerability. However, the proportion has fallen a bit, in terms of the conventional view of developed countries taking the approach of transferring responsibility to developing countries. Instead, the proportions of transferring responsibility between developing countries have rose by 10% to 30% during 2005-2015, partially due to stronger trade ties among developing countries. Our findings support policy decisions on tracing environmental responsibility for water scarcity and call for action to prevent water ecological downsides due to international trade.

Local and non-local drivers of consumption-based water use in China during 2007-2015: Perspective of metacoupling

Increasingly growing consumption-based water use (WU) combined with climate change have exacerbated water stress globally and regionally, yet little is known about how the WU change is affected by metacoupled processes which involve human-nature interactions across space; within and across adjacent and distant places. This study aims to unveil the spatio-temporal pattern of China's WUs during 2007-2015 and its underlying local and non-local drivers. Results show that China's total WU exhibited an upward trend from 386.7 billion m³; in 2007 to 431.2 billion m³ in 2012 but dropped to 412.6 billion m³ by 2015. Widespread and continuous water use efficiency improvement contributed most to offsetting the increase in WU driven by the rising affluence and growing population in the context of rapid urbanization and industrialization. Economic structure drove a relatively large WU reduction (responsible for -23.7% of the WU change during 2007-2015), in line with China's ongoing transform from a capital investment-driven economy to a consumption-driven one and decoupling economic growth from environmental pressure. The population share representing the non-local factor of migration effect was large enough to be seen clearly in the changing WUs across China: the WUs of coastal areas ascended while inland areas descended, which was in accordance with migration patterns. Our findings could make a valuable contribution to decision-making in identifying hotspot areas, charting systematic courses for sustainable water use, and combining demand-oriented and supply-oriented measures.

Assessment of Sectoral Virtual Water Flows and Future Water Requirement in Agriculture Under SSP-RCP Scenarios: Reflections for Water Resources Management in Zhangye City

Water scarcity is a core issue that constraints the high-quality development of arid areas in northwestern China. Zhangye is an oasis city located in the Heihe River Basin in northwestern China. It is populated with an agriculture-dominated economy and faces more and more serious water crises. Virtual water is an indicator that can measure the embodied water in the traded products, which has been widely applied for making rational policies for water resources management. In addition, clarifying water requirements in agricultural sectors under future climate change scenarios is essential to develop more appropriate adaptation strategies. From this perspective, this study aims to evaluate and compare virtual water flows among various sectors in Zhangye for the years 2012 and 2017 with a single regional input-output model and to further clarify the future water requirement tendency in agriculture during 2020–2050 under different shared socioeconomic pathways and representative concentration pathways (SSP-RCP) scenarios. The results showed that the planting sector directly contributed most of the total water consumption with the highest direct coefficient of 3307.5 m3/yuan in 2012, whereas the manufacture of food products and tobacco processing sector had the largest proportion of indirect water consumption (99%) mainly from intermediate inputs of agricultural products. Water consumption intensity of all sectors on average decreased by 22% during 2012–2017, indicating an increasing water utilization efficiency in economic industries. Household consumption also can improve water utilization efficiency as the major pathway for final consumption (86.4% in 2017). Water scarcity in Zhangye was becoming increasingly prominent since virtual water net exports were higher than local consumption, especially in the agriculture, manufacturing, and energy supply industries. Moreover, under climate change scenarios, we found the highest level of water requirement per unit area occurred in 2000, but it still had an incremental potential by 2050, especially in SSP585. The high requirement intensity and large-scale maize planting caused a rising tendency of total crop water requirement with an annual increasing rate of 8.4% from 1980 to 2050. This makes it possible to adapt to climate change through scientific management measures and technical means. We further made policy implications for adaptive management of water resources in Zhangye.

Assessing sectoral water stress states from the demand-side perspective through water footprint dimensions decomposition

Due to its essentiality and scarcity, water is subject to stress from the supply and demand side. The SDG and many methods for assessing water stress (WS) are based on water supply, even though the total water supply is uncontrollable by humans in the short term. Conversely, from a water demand perspective, WS arises from the deliberate and manageable use of water to produce goods and services, with few methods proposing to evaluate WS. We propose a method to assess the sectoral demand-side water stress states (DWSS) to fill this gap. The method comprises a quantitative step followed by a qualitative analysis. Quantitatively, an environmentally extended input-output model integrated Brazilian water resource and economic data for 2010 and 2015, including the imported virtual water in the water footprint calculation. Three dimensions of water footprint (DWF) were calculated: consumptive use of water (CUWF), water consumption (CWF), and return to the environment (REWF). The variations in DWFs over time were used as criteria to define five DWSS ranging from weak to strong. Brazilian economy as a whole presented a moderately weak DWSS. Among economic sectors, the most frequent DWSS was moderately weak, with sixteen sectors. The Livestock and Forestry, fishing, and aquaculture sectors had a strong DWSS, while the Slaughter, meat, and dairy and Public administration sectors had weak DWSS. Despite its limitations, the demand-side analysis can complement the usual method from a supply perspective.

Green water appropriation of the cropland ecosystem in China

Despite the awareness that green water is the main source of water to produce food, studies on green water use in cropland ecosystems are still rather limited, and almost no research has so far explored the relationship between green water utilization and socioeconomic development. In this study, with the help of CropWat 8.0, the green water footprint (GWF) of main crops in China was estimated from 1979 to 2016. On this basis, a novel concept, i.e., green water appropriation rate (GWar), was introduced to reveal the relationship between GWF and precipitation. Then, for the first time, the center of gravity trajectory of the GWar and the correlation between GWar and socioeconomic factors were further investigated. The results show that the provinces with the largest increases of GWF were Inner Mongolia (223%), Xinjiang (127%), and Ningxia (123%), while the GWF of 11 provinces has decreased, and 9 of them were municipalities or coastal areas. Generally, the GWar in the eastern and central provinces was higher than that in the western provinces. The center of gravity of the GWar has always been in Henan Province, but it has moved westward from Kaifeng City in 1979 to Sanmenxia City in 2016 and may further move to Shanxi Province soon. The total power of agricultural machinery and the effective irrigation rate had a positive correlation with the GWar, while the agricultural GDP was negatively correlated with the GWar. It is expected that the results will explicitly provide a scientific basis for the development of water-appropriate agriculture and the full utilization of rainwater.

Water-energy-carbon nexus in China's intra and inter-regional trade

Water consumption, energy use, and carbon emission are three related key anthropogenic impacts on the natural environment. China is the largest carbon emitter and energy consumer, with the serious unevenly distributed water resources. Therefore, investigating the water-energy-carbon (WEC) nexus is important for China's environmental footprint reduction. This study explores the relation between water utilization, energy consumption, and carbon emission in China, based on a multiregional input-output (MRIO) analysis. The WEC nexus is discussed comprehensively in consideration of the utilization of water and energy and the emission of carbon, as well as the trade to and from and the consumption activities in different sectors and provinces. Results show that water, energy, and carbon present significant consistency in production and consumption processes. Sectors with higher consumption coefficients dominate the transfer of virtual WEC. Although virtual WEC mainly transfers from less developed regions to relatively developed regions, Category 1 (i.e., WEC all import) and category 2 (i.e., WEC disaccord) present opposite results to and category 3 (i.e., WEC all export) provinces in terms of W-E and W-C nexus. The net water and energy transfers are significantly positively correlated in category 1 provinces, whereas both sides are negatively correlated in category 2 and 3 provinces. This phenomenon also exists in the relationship between net water and carbon transfers. The virtual water, as well as energy and carbon export pressures are dispersed in these export provinces. Findings of this study are expected to assist the government in decreasing the environmental footprints and achieve sustainable development in China.

Environmental Consequences of Potential Strategies for China to Prepare for Natural Gas Import Disruptions

Worldwide efforts to switch away from coal have increased the reliance on natural gas imports for countries with inadequate domestic production. In preparing for potential gas import disruptions, there have been limited attempts to quantify the environmental and human health impacts of different options and incorporate them into decision-making. Here, we analyze the air pollution, human health, carbon emissions, and water consumption impacts under a set of planning strategies to prepare for potentially fully disrupted natural gas imports in China. We find that, with China's current natural gas storage capacity, compensating for natural gas import disruptions using domestic fossil fuels (with the current average combustion technology) could lead up to 23,300 (95% CI: 22,100-24,500) excess premature deaths from air pollution, along with increased carbon emissions and aggravated water stress. Improving energy efficiency, more progressive electrification and decarbonization, cleaner fossil combustion, and expanding natural gas storage capacity can significantly reduce the number of excess premature deaths and may offer opportunities to reduce negative carbon and water impacts simultaneously. Our results highlight the importance for China to increase the domestic storage capacity in the short term, and more importantly, to promote a clean energy transition to avoid potentially substantial environmental consequences under intensifying geopolitical uncertainties in China. Therefore, mitigating potential negative environmental impacts related to insecure natural gas supply provides additional incentives for China to facilitate a clean and efficient energy system transition.

Exploring solutions to alleviate the regional water stress from virtual water flows in China

China has long faced an uneven distribution of physical water resources, which has been further exacerbated by the virtual water transfers embodied in the interregional trade. To alleviate such unfavorable influences of interregional virtual water flows on regional water scarcity, this paper first combined a multi-regional input-output model and a structural decomposition analysis to identify the major driving forces behind the changes in interregional virtual water flows from 2002 to 2012, and then conducted a scenario analysis to explore solutions for sustainable water resource management in China. Results indicated that the virtual water outflows from water-deficient developing regions (Northwest and Northeast) to water-abundant developed regions, such as East Coast and South Coast, have been increasingly intensified from 2002 to 2012. During the period, the final demand predominated the increase of virtual water transfers, while the improvement of water use efficiency dominated the decline in virtual water flows from 2002 to 2012. Results from the designed scenarios indicated that the negative impacts of interregional virtual water flows on the water stress can be effectively relieved, indicating the high priority of regional water use efficiency improvement, especially in water-starved regions.

The Impact of Scarcity of Medical Protective Products on Chinese Consumers’ Impulsive Purchasing during the COVID-19 Epidemic in China

In 2020, during the peak period of the COVID-19 outbreak in China, the scarcity of medical protective products significantly influenced consumers’ impulsive purchasing and affected the public order. It is important to identify the effect of scarcity on consumers’ impulsive purchasing during this difficult time. However, scant research has been conducted on the impact of scarcity of medical protective products on Chinese consumers’ impulsive purchasing. This paper investigates the impact of the scarcity of medical protective products on consumers’ impulsive purchasing during the pandemic in China based on the theories of scarcity, S-O-R and bandwagon effect. Simultaneously, this study identifies the different mediating mechanisms (fear of missing out and perception) and the moderation (bandwagon) in the relationship between scarcity and impulsive purchasing. Finally, 509 validity data were collected by using an online questionnaire, and SmartPLS was used for data analysis. The findings present that the fear of missing out, perception and bandwagon dominate the scarcity effect on impulsive purchasing. The findings provide more information on consumers’ impulsive purchasing in the context of scarcity of medical protective products. Marketers and the Chinese government can adopt measures to reduce their effect, which may help maintain the public order during the epidemic.

A factorial emission-focused general equilibrium model for investigating composite effects of multiple environmental policies

With the rapid growth of the economy, there are increasing conflicts between economic development and environmental protection. Among these conflicts, the wastewater emission management as one of the significant ways to alleviate water scarcity has been paid increasing attention across the developing countries, such as China. It is thus essential to comprehensively investigate the enviro-economic effects induced by wastewater-related policies. In this study, a factorial emission-focused general equilibrium model (FEGE) is first developed to facilitate examine the composite enviro-economic effects of multiple policy scenarios with regards to wastewater-related environmental taxes and the related subsides. A special case study for the Municipality of Chongqing, China, is conducted to illustrate the potential benefits of its use in the formulation of wastewater-related policies. It is found that the impacts of various wastewater-related policies (i.e., environmental taxes and the related subside) on GDP are different. In detail, green tax policies on GDP are negative, while wastewater emission intensity (WEI) improvement policies on GDP are positive. When green tax reaches 14 yuan/tonne, which is the maximum proposed by the Chinese government, the GDP will drop by 0.37%, which would be deemed acceptable for the Municipality of Chongqing. In addition, the impacts on rural households' consumption are greater than those on urban households' consumption whichever the application of wastewater-related policies; it is because the rural households in the Municipality of Chongqing have a relatively unitary income source. It is thus recommended that the rural household in Chongqing should be paid more attention. For example, some extra allowances could be considered to the rural household to help them cope with the negative economic impacts induced by a new environmental policy. It is expected that the outputs would provide bases for formulating desired wastewater-related policies.

Evaluating Cryospheric Water Withdrawal and Virtual Water Flows in Tarim River Basin of China: An Input–Output Analysis

In Tarim River Basin (TRB), the retreat of glacier and snow cover reduction due to climate warming threatens the regional economy of downstream basins that critically depends on meltwater. However, the quantitative evaluation of its impact on multiple sectors of the socioeconomic system is incomplete. Based on compiled regional input–output table of the year 2012, this study developed a method to analyze the relationships between economic activities and related meltwater withdrawal, as well as sectoral transfer. The results show that the direct meltwater withdrawal intensity (DMWI) of agriculture was much higher than other sectors, reaching 2348.02 m3/10,000 CNY. Except for A01 (agriculture) and A02 (mining and washing of coal), the embodied meltwater withdrawal (EMW) driven by the final demand of other sectors was greater than direct meltwater withdrawal, and all sectors required inflows of virtual water (72.45 × 108 m3, accounting for 29% of total supply from cryospheric water resources) for their production processes in 2012. For sectors with high DMWI, improving water-use efficiency is an effective way to reduce water withdrawal. To some extent, the unbalanced supply of cryospheric water resources due to geographical segregation can be regulated by virtual water flows from water-saving to water-intensive sectors. Such decisions can affect the balance between socioeconomic development and environment conservation for long-term sustainability.

What the reclaimed water use can change: From a perspective of inter-provincial virtual water network

Reclaimed water has been used as an alternative water resource for various economic activities, which inevitably is involved in the virtual water trade. However, the effect of reclaimed water on the virtual water trade has not been evaluated in previous studies. For the sake of sustainable water management, this study explored the benefits of reclaimed water use for balancing the water resource allocation at the interprovincial level. Multiregional input-output analysis and ecological network analysis were used to investigate the spatial and structural characteristics of the virtual reclaimed water network (VRWN) among 31 provinces in China and the potential effect of reclaimed water use. The results show that the net export flows of virtual reclaimed water have different spatial patterns from those of freshwater, some provinces that import virtual freshwater are exporters of virtual reclaimed water. Although the exploitative relationship is the dominant ecological relationship in the VRWN (72%), it is confirmed that reclaimed water use contributes to balancing the virtual water trade of China with a more competitive relationship (21%) than in the virtual freshwater network (4%). The virtual freshwater consumption change rate in developed provinces decreases by more than 10% through reclaimed water use. Due to the high food exports and low application of wastewater reclamation in less developed provinces, the effect of reclaimed water use in those provinces is not as obvious as that in developed provinces. This paper offers a new perspective for understanding the current VRWN and guidance for the optimization of the virtual water trade structure.

Is the Water System Healthy in Urban Agglomerations? A Perspective from the Water Metabolism Network

Urban agglomerations are a primary spatial focus of socioeconomic activity and inherently include large volumes of embodied water. We have applied the concept of water metabolism health to comprehensively evaluate the overall operation of water systems in urban agglomerations and propose an innovative assessment framework. In particular, we constructed a water metabolism network (WMN) model to simulate a water system in which different cities and sectors are integrated, combining a newly compiled multiregional input-output (MRIO) table of water flow with ecological network analysis (ENA). A case study considering the Pearl River Delta (PRD) urban agglomeration in 2015 demonstrates that its network is well synergic but highly dependent, with considerable negative effects. Highly developed cities in southeastern of the PRD exhibit higher embodied water productivity and robustness but impose considerable negative effects on the water system. We found the agricultural sector to be a dominant controller of the network; the construction and service sectors represent the primary beneficiaries with strong competition. We suggest measures at various scales to improve water utilization efficiency and promote positive interactions between components, thus improving water metabolism system health for urban agglomerations.

Quantifying economic-social-environmental trade-offs and synergies of water-supply constraints: An application to the capital region of China

Sustainable water management is one of the sustainable development goals (SDGs) and is characterized by a high level of interdependencies with other SDGs from regional to global scales. Many water assessment studies are restricted to silo thinking, mostly focusing on water-related consequences, while lacking a quantification of trade-offs and synergies of economic, social, and environmental dimensions. To fill this knowledge gap, we propose a "nexus" approach that integrates a water supply constrained multi-regional input-output (mixed MRIO) model, scenario analysis, and multi-criteria decision analysis (MCDA) to quantify the trade-offs and synergies at the sectoral level for the capital region of China, i.e. the Beijing-Tianjin-Hebei urban agglomeration. A total of 120 industrial transition scenarios including nine major industries with high water-intensities and water consumption under current development pathways were developed to facilitate the trade-off and synergy analysis between economic loss, social goals (here, the number of jobs) and environmental protection (with grey water footprint representing water pollution) triggered by water conservation measures. Our simulation results show that an imposition of a tolerable water constraint (a necessary water consumption reduction for regional water stress level to move from severe to moderate) in the region would result in an average economic loss of 68.4 (± 16.0) billion Yuan (1 yuan ≈ 0.158 USD$ in 2012), or 1.3 % of regional GDP, a loss of 1.94 (± 0.18) million jobs (i.e. 3.5 % of the work force) and a reduction of 1.27 (± 0.40) billion m³ or about 2.2% of the regional grey water footprint. A tolerable water rationing in water-intensive sectors such as Agriculture, Food and tobacco processing, Electricity and heating power production and Chemicals would result in the lowest economic and job losses and the largest environmental benefits. Based on MCDA, we selected the 10 best scenarios with regard to their economic, social and environmental performances as references for guiding future water management and suggested industrial transition policies. This integrated approach could be a powerful policy support tool for 1) assessing trade-offs and synergies among multiple criteria and across multiple region-sectors under resource constraints; 2) quantifying the short-term supply-chain effects of different containment measures, and 3) facilitating more insightful evaluation of SDGs at the regional level so as to determine priorities for local governments and practitioners to achieve SDGs.

Driving Forces of Food Consumption Water Footprint in North China

The water footprint (WF) vividly links water resources with virtual water of food, providing a novel perspective on food demand and water resources management. This study estimates the per capita WF of food consumption for six provinces in North China. Then, the study applies the logarithmic mean Divisia index method to decompose the driving forces of their WF changes. Results show that the per capita WF of food consumption in Beijing, Tianjin, and Inner Mongolia increases significantly in 2005–2017, whereas that in the other three provinces in North China varies slightly. All provinces have shown the same trend of food structure changes: the grain decreased, whereas the meat increased. In general, the urban effect was positive, and the rural effect was negative for all regions. The urban effects in Beijing and Tianjin played a leading role, whereas the rural effects in the other four provinces played a leading role from 2005–2009. However, the urban effects in all provinces played a leading role in 2010–2017. The WF efficiency increased in each province, and the effect in urban areas is stronger due to the higher water use efficiency. For most provinces, the consumption structure was positive because the diet shifted toward more meat consumption. The food consumption per capita effect was the major driving force in Beijing and Tianjin due to the increased consumption level, whereas the population proportion effect exerted a weak effect. To alleviate the pressure on water resources, further improving water use efficiency in food production and changing the planting structure should be emphasized for all regions in North China.

Social network analysis of virtual water trade among major countries in the world

This study utilizes multi-region input-output model to calculate the virtual water trade among 19 major countries (the Group 20 countries, except the EU) from 2006 to 2015. Moreover, this paper uses network analysis method to study the characteristics of virtual water trade networks. Results show that: (1) the import and export of the virtual water trade among 19 major countries in 2015 increased in varying degrees. Among them, the growth rates of China's import and Russia's export were the highest. (2) The density(average value) and asymmetry(differences between import and export)of the virtual water trade network among the major countries in 2006-2015 increased throughout the whole industry and the three major industries. In comparison with the secondary and tertiary industries, the virtual water trade network formed by the primary industry is denser. (3) The Out-Degree(corresponding to export) and In-Degree(corresponding to import)of countries in the virtual water trade network of the whole industry increased in varying degrees in 2015. Major countries exhibited the largest export and import within the primary industry, except for Japan and South Korea. Therefore, in order to alleviate the contradiction between supply and demand of water resources in various countries, it is necessary to further strengthen the construction of transportation facilities and reduce the logistics cost of trade in industrial and agricultural products, especially the trade cost of agricultural products such as grain, so as to further expand the virtual water import and export trade to expand the import and export trade of the virtual water network further.

A Review of Water Stress and Water Footprint Accounting

Production and consumption activities deplete freshwater, generate water pollution and may further lead to water stress. The accurate measurement of water stress is a precondition for sustainable water management. This paper reviews the literature on physical water stress induced by blue and green water use and by water pollution. Specifically, we clarify several key concepts (i.e., water stress, scarcity, availability, withdrawal, consumption and the water footprint) for water stress evaluation, and review physical water stress indicators in terms of quantity and quality. Furthermore, we identify research gaps in physical water stress assessment, related to environmental flow requirements, return flows, outsourcing of water pollution and standardization of terminology and approaches. These research gaps can serve as venues for further research dealing with the evaluation and reduction of water stress.

Blue water footprint linked to national consumption and international trade is unsustainable

Increasing pressure on the world's freshwater resources raises serious concerns about global food security and the sustainability of water use in agriculture. Here we quantify and map at a 5-arcmin spatial resolution the blue water footprint of each country's national consumption and where they infringe sustainable environmental flows as defined by the presumptive environmental flow standard or the 80% rule, in which runoff depletion by more than 20% will pose risk to ecosystems. We find that 52% of the blue water footprint of global consumption and 43% of international blue virtual water flows come from places where the sustainable environmental flow is violated. About 22% of the environmental flow infringement of the blue water footprint of global consumption lies outside the specific countries of consumption, indicating that a number of them have externalized their impacts. By establishing a link between the consumption of a product in one place and water scarcity in places far from the place of consumption, our assessment may aid a dialogue on how to assign and share responsibilities concerning water use.

Spillover risk analysis of virtual water trade based on multi-regional input-output model -A case study

Massive amounts of water embodied in commodities are transferred via interregional trade which increase the water scarcity risk of exporting region. This study proposed an integrated evaluation framework for sectoral physical water use risks and virtual water flow risks in Northeast China. The initial water use risks for different sectors by provinces were first assessed based on sectoral physical water consumption. Then based on the multi-regional input-output (MRIO) model, a virtual water trade network was established, and simultaneously the virtual scarce water in sectoral export of intermediate goods and final goods were accounted to investigate the virtual water flow risks by sectors. Finally, interprovincial embodied scarce water transfers between Northeast China and the rest of China were mapped, and by grafting the concept of 'spillover risk' to the virtual water trade, we analyzed the spillover risk difference of virtual water trade between regions. The results showed that the sectors of Agriculture (Ag) and Other manufacturing (OM) presented the highest risk of water use while Nonmetal mining (NmM) belonged to the potential high-risk sectors of water use for Northeast China. The sectors exported more virtual scarce water in intermediate goods also exported more in the final goods; and the sector of Manufacture of food products and tobacco processing (FP) was the largest contributor to the large exporting virtual scarce water for Liaoning and Jilin while Ag in Heilongjiang province was the largest exporter. The cumulative spillover risk index from rest of China to Liaoning province through virtual water trade is the highest; and the main risk spilt provinces to Northeast China were Xinjiang, Jiangsu, Anhui and Hebei province. The proposed risk framework for water utilization and trade may help promote the redistribution of water resources and explore pathways for sustainable management of water resources.

Spatio-Temporal Variations of Crop Water Footprint and Its Influencing Factors in Xinjiang, China during 1988–2017

Scientifically determining agricultural water consumption is fundamental to the optimum allocation and regulation of regional water resources. However, traditional statistical methods used for determining agricultural water consumption in China do not reflect the actual use of water resources. This paper determined the variation in the crop water footprint (CWF) to reflect the actual agricultural water consumption in Xinjiang, China, during the past 30 years, and the data from 15 crops were included. In addition, the STIRPAT (stochastic impacts by regression on population, affluence and technology) model was used to determine the factors influencing the CWF. The results showed that the CWF in Xinjiang increased by 256% during the 30-year period. Factors such as population, agricultural added value, and effective irrigated area were correlated with an increase in the CWF. This study also showed that the implementation of national and regional policies significantly accelerated the expansion of agricultural production areas and increased the amount of agricultural water used. The objectives of this paper were to identify the factors influencing the CWF, give a new perspective for further analysis of the relationship between agricultural growth and water resources utilization, and provide a reference for local policy decision-makers in Xinjiang.

Exploring consumption-based planetary boundary indicators: An absolute water footprinting assessment of Chinese provinces and cities

The water planetary boundary (PB) has attracted wide academic attention, but empirical water footprint research that accommodates local biophysical boundaries remains scarce. Here we develop two novel quantitative footprint indicators, the water exceedance footprint and the surplus water footprint. The first measures the amount of excessive water withdrawal (exceeded amount of water withdrawn against local water PBs) and the latter evaluates the potential of surplus water that can be sustainably utilised (amount of surplus water available within local water PBs). We quantify the extent to which demand for goods and services in Chinese provinces and cities are driving excessive withdrawal of local and global water resources. We investigate both territorial and consumption-based water withdrawal deficit and surplus against local water withdrawal PBs. We also trace how PB-exceeded water and surplus water are appropriated for producing certain commodities. In 2015, China's domestic water exceedance reaches 101 km³ while the total water exceedance footprint is 92 km³. We find that 47% of domestic excessive water withdrawal is associated with interprovincial trade. Exceeded water transfers were dominated by agricultural trade from the drier North to the wetter South. A revised virtual water trade network informed by exceedance and surplus water footprint metrics could help address sustainability concerns that arise from the trade of water-intensive commodities. Our findings highlight that policy targets need to accommodate PB exceedance of both direct and virtual water use.

Interprovincial food trade and water resources conservation in China

A spatial mismatch in water and arable land availability results in large virtual water transfers through interprovincial food trade in China. Accurately identifying and measuring water-saving links in interprovincial food trade can help to relieve water resources pressure in main grain-producing areas. We use a multiregional input-output table combined with the CROPWAT model to build China's interprovincial virtual water transfer network embedded in food trade in 2012. Then, water saving and scarce water saving are measured. Both consider the difference in water productivity among provinces, but the latter also pays attention to the scarcity of water resources. Finally, we adopt a water footprint to recalculate the scarce water savings without precipitation (green water). Our results indicate that the amount of virtual water transfer embedded in food trade is 74.9 billion m³, which is equivalent to 12.22% of the total water use in 2012. We observe large variations in the relationship between water resources abundance and agricultural water-use efficiency across provinces. Especially, there is a virtual water transfer from provinces with high water productivity but a lack of water to provinces with low water productivity but an abundance of water. The scarce water saving can identify sustainable food trade links, which can alleviate water scarcity in consuming provinces without exacerbating water shortage in producing provinces. In addition, interprovincial food trade results in 15 billion m³ of scarce gray water saving, which is equivalent to 59.76% of the scarce blue water saving. Scarce water saving based on blue water and gray water provides a basis for establishing an interprovincial compensation mechanism to balance the cost of water redistribution caused by food trade.

Globalized energy-water nexus through international trade: The dominant role of non-energy commodities for worldwide energy-related water use

The increasing energy demand in future will inevitably escalate pressures on water resources, as energy production needs huge amounts of water inputs. Globalization has resulted in the geographic separation between the source of water inputs for energy production and the sink of its final consumption, making it crucial to factor global supply chain effect into water-energy nexus management. Therefore, this paper investigates water use for energy from source of exploitation to sink of final consumption along global supply chains based on embodiment accounting method. In total, the energy-related water use embodied in international trade is in magnitude about 80% of global total energy-related water use in 2011. It should be noted that non-energy commodities contribute more than four fifths of energy-related water use embodied in international trade and global final consumption. China serves the largest exporter of energy-related water use while EU28 is the biggest receiver. From a perspective of global supply chains, two thirds of USA direct energy-related water use sinks into final consumption from rest of the world, and over a quarter of that embodied in Mainland China's final consumption is from USA, showing the tight relation between them on global supply chains. Findings highlight the urgent need to consider international trade (i.e., energy and non-energy commodity trade) and global supply chain effects for water-energy nexus policy-making to ensure the sustainable water supply for energy development.

Multi-dimensional diagnosis model for the sustainable development of regions facing water scarcity problem: A case study for Guangdong, China

Freshwater consumption and wastewater discharge of economic activities have caused water scarcity problem in many regions. This study aims to develop a multi-dimensional diagnosis model (MDDM) to provide new insights for the sustainable development of regions which face water scarcity problem. In detail, the sectorial blue water, grey water and total water consumptions are assessed to reveal the direct effects of economic activities on water quantity and water quality. Then, hypothetical extraction method is integrated into input-output model and ecological network analysis to quantify the system-based effects of sectors in three dimensions: economy, water and metabolism. A case study of Guangdong province, China is conducted to illustrate the availability of the developed model. We found that the multi-dimensional performances of Guangdong's socioeconomic system are dominated by a few sectors. Wastewater, especially that discharged from the primary industry, is the main reason for the local water scarcity. Specifically, the unique role that every sector plays in the socioeconomic system is quantitatively revealed by MDDM, which could guide the relevant policy development at sectorial level.

Tension of Agricultural Land and Water Use in China's Trade: Tele-Connections, Hidden Drivers and Potential Solutions

Interregional trade can potentially extend the management of scarce resources beyond a region's territory along supply chains. Here we combined the multiregional input-output model with structural decomposition analysis to reveal the distant connections of agricultural land and water use as well as the drivers behind their variations in China. Our results show that trade-embodied agricultural land use increase by 2.3-fold and 2.5-fold for virtual agricultural water use flows from 2002 to 2012. The water-starved northern China with abundant agricultural land is the main exporter of virtual (also called trade-embodied) agricultural land and water. Moreover, the role of the virtual water use importers and exporters were determined by the availability of land, rather than water resources. Based on scenario analysis, we found that if agricultural water use efficiency of north China reached the world's top-level but agricultural land use efficiency remained unchanged, the virtual water flows would be reduced by 32% and only water resources, not agricultural land, would be able to sustain future economic development. Our findings may provide significant information for potential solutions to China's regional water shortage from a land-water nexus perspective.

Uneven development within China: Implications for interprovincial energy, water and arable land requirements

Owing to uneven development and unbalanced resource endowments within China, ensuring reliable energy, water and food supply is a core challenge to regional socio-economic development. This study makes a first attempt to examine and compare demand-driven energy, water and arable land (E-W-L) resource outsourcings within China based on the latest multi-regional input-output model. Results show that interprovincial trade reallocated 73.4%, 33.9% and 38.1% of the national total E-W-L resource inputs in 2012, respectively. Investment was the dominant final demand category for driving energy requirements, while consumption was the leading final demand category for water and arable land requirements. Important provincial regions and critical transmission sectors for the trade of embodied E-W-L resources are identified. Substantial E-W-L resources were transferred from the central and western regions to the eastern regions. Especially, Inner Mongolia was the top interregional net exporter of embodied energy, while Jiangsu topped the net importer list. Regarding virtual water transfer, Xinjiang and Shandong were the biggest interregional net exporters and net importers, respectively, while Heilongjiang and Guangdong stood out in the net trade of embodied arable land. Owing to the impact of interprovincial trade, the resource occupancy levels of the eastern developed area were much higher than those of the northeastern, central and western areas. The imbalances in the levels of socio-economic development amongst provincial regions are mirrored by their patterns of E-W-L uses and related trade transfer. Understanding the synchronal outsourcings of E-W-L resource requirements provides important implications for targeted resource management in Chinese interprovincial supply chains.

Urban Multi-Source Water Supply in China: Variation Tendency, Modeling Methods and Challenges

Urban water resources are the basis for the formation and development of cities and the source of urban water supply. However, with the acceleration of urbanization and the explosion of urban populations, the contradiction between water supply and demand in some areas, especially in big cities, has become increasingly prominent. It is simply not sufficient to rely on local conventional water resources to meet urban water demand, and a single source water supply mode has a higher vulnerability, resulting in greater safety risks in urban or regional water supply systems. Therefore, giving full play to the water supply capacity and carrying out multi-source water supplies are necessary and urgent. This paper gives an overview of the optimal allocation of multi-source for urban water supply concerning variation tendency, modeling methods and facing challenges. Based on the variation tendency of water consumption and water supply pattern in China, Tianjin is taken as a typical city for systematically outlining water supply changes and cause analysis. Subsequently, the modeling methods for proposing the optimal allocation scheme are summarized, which are composed of defining the topological relation, constructing the mathematical model and seeking the optimal solution. Ultimately, the current and emerging challenges are discussed including emergency operation of multi-source water supply and joint operation of water quality and quantity. These summaries and prospects provide a valuable reference for giving full play to the multi-source water supply capacity and carrying out relevant research so as to propose the optimal allocation scheme in urban multi-source water supply systems.

Projecting China's future water footprint under the shared socio-economic pathways

Increasing water scarcity in China is further exacerbated by the rapid socio-economic development and uneven spatial distribution of water resources. Current studies on water footprint have mainly focused on historical accounting and trend analysis at the provincial scale. However, a comprehensive exploration of future water footprint would be vital to a better understanding of future water shortage challenges, and more importantly, would allow the mitigation of water scarcity and inequal water distribution. In this paper, we present an approach to project the future water footprint of China at a fine resolution (0.125 arc-degree) under the shared socio-economic pathway (SSP) scenario framework, which described five future alternative socio-economic development pathways over the 21st century. We first simulated the future spatial patterns of built-up land using the Future Land Use Simulation (FLUS) model and derived the future population growth and urbanization rate from the population projection provided by the National Center for Atmospheric Research (NCAR). Then future water footprint was projected according a log-transformed linear regression calibrated with historical data during 2007-2012. We found that the total volume of China's water footprint will increase significantly in the future under the SSP1, SSP4 and SSP5 scenarios, reaching up to nearly 400 billion m³ in 2050, equivalent to almost 40% increase compared to that in 2010. The spatial patterns of future water footprint show dramatic increase (up to 100-130%) in the eastern provinces (Shandong, Henan, and Hebei), and slight decrease were found in the western provinces (Xinjiang, Ningxia, and Qinghai). In addition, the future water footprints were found to share very similar spatial patterns at local pixel scale among different SSP scenarios in three of the largest metropolitan areas of China (Beijing-Hebei-Tianjin, Yangtze River Delta, and Pearl River Delta). These findings provide extensive knowledge of the future water footprint and suggest a more severe water scarcity in the future from a consumption-oriented perspective. More effective water management policies are urgently needed to mitigate future water resource scarcity and inequality.

Virtual Water Flows Embodied in International and Interprovincial Trade of Yellow River Basin: A Multiregional Input-Output Analysis

With the imminent need of regional environmental protection and sustainable economic development, the concept of virtual water is widely used to solve the problem of regional water shortage. In this paper, nine provinces, namely Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan, and Shandong in the Yellow River Basin (YRB), are taken as the research objects. Through the analysis of input-output tables of 30 provinces in China in 2012, the characteristics of virtual water trade in this region are estimated by using a multi-regional input-output (MRIO) model. The results show that: (1) The YRB had a net inflow of 17.387 billion m³ of virtual water in 2012. In interprovincial trade, other provinces outside the basin export 21.721 billion m³ of virtual water into the basin. In international trade, the basin exports 4334 million m³ of virtual water to the international market. (2) There are different virtual flow paths in the basin. Shanxi net inputs virtual water by interprovincial trade and international trade, while Gansu and Ningxia net output virtual water by interprovincial trade and international trade. The other six provinces all net output virtual water through international trade, and obtain the net input of virtual water from other provinces outside the basin. (3) From the industrial structure of the provinces in the basin, the provinces with a relatively developed economy, such as Shandong and Shanxi, mostly import virtual water in the agricultural sector, while relatively developing provinces, such as Gansu and Ningxia, mostly import virtual water in the industrial sector. In order to sustain the overall high-quality development of the YRB, we propose the virtual water trade method to quantify the net flow of virtual water in each province and suggest the compensation responsibility of the virtual water net inflow area, and the compensation need of the virtual water net outflow area, in order to achieve efficient water resources utilization.

Pollution exacerbates China's water scarcity and its regional inequality

Inadequate water quality can mean that water is unsuitable for a variety of human uses, thus exacerbating freshwater scarcity. Previous large-scale water scarcity assessments mostly focused on the availability of sufficient freshwater quantity for providing supplies, but neglected the quality constraints on water usability. Here we report a comprehensive nationwide water scarcity assessment in China, which explicitly includes quality requirements for human water uses. We highlight the necessity of incorporating water scarcity assessment at multiple temporal and geographic scales. Our results show that inadequate water quality exacerbates China's water scarcity, which is unevenly distributed across the country. North China often suffers water scarcity throughout the year, whereas South China, despite sufficient quantities, experiences seasonal water scarcity due to inadequate quality. Over half of the population are affected by water scarcity, pointing to an urgent need for improving freshwater quantity and quality management to cope with water scarcity.

Water for maize for pigs for pork: An analysis of inter-provincial trade in China

Trade in commodities implies trade in virtual water (VW), which refers to the water that was used to produce the traded goods. Various studies have quantified international or inter-provincial virtual water (VW) flows related to the trade in crops and animal products. Until date, however, no effort has been undertaken to understand how the water embodied in traded feed crops (trade stage TS1) will be transferred further because of trade in animal products (trade stage TS2). This is the first study showing this mechanism, in a case study in China for maize (the major pig feed) and pork (the dominant meat), considering the period 2000-2013. We estimate the annual green and blue water footprints in maize production and then quantify the inter-provincial VW flows related to trade in maize (TS1) and trade in maize embodied in pork (TS2). Results show that in TS1, maize-related VW flowed from the water-scarce North to the water-rich South, with an increase of 40% over the study period (from 43 to 61 billion m³ y^-1). In TS2, about 10% of the water embodied in maize exports from North to South China returns in the form of pork, with an increase in the absolute amount of 25% (from 4.8 to 6.1 billion m³ y^-1). Considering blue VW flows specifically, we find that North-to-South blue VW flows decreased by 5% in TS1, while South-to-North blue VW flows increased by 23% in TS2.