Physical water scarcity metrics for monitoring progress towards SDG target 6.4: An evaluation of indicator 6.4.2 "Level of water stress"

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.

Environmental assessment of diets: overview and guidance on indicator choice

Comprehensive but interpretable assessment of the environmental performance of diets involves choosing a set of appropriate indicators. Current knowledge and data gaps on the origin of dietary foodstuffs restrict use of indicators relying on site-specific information. This Personal View summarises commonly used indicators for assessing the environmental performance of diets, briefly outlines their benefits and drawbacks, and provides recommendations on indicator choices for actors across multiple fields involved in activities that include the environmental assessment of diets. We then provide recommendations on indicator choices for actors across multiple fields involved in activities that use environmental assessments, such as health and nutrition experts, policy makers, decision makers, and private-sector and public-sector sustainability officers. We recommend that environmental assessment of diets should include indicators for at least the five following areas: climate change, biosphere integrity, blue water consumption, novel entities, and impacts on natural resources (especially wild fish stocks), to capture important environmental trade-offs. If more indicators can be handled in the assessment, indicators to capture impacts related to land use quantity and quality and green water consumption should be used. For ambitious assessments, indicators related to biogeochemical flows, stratospheric ozone depletion, and energy use can be added.

Progress on SDG 7 achieved by EU countries in relation to the target year 2030: A multidimensional indicator analysis using dynamic relative taxonomy

In 2015, 193 UN members adopted the resolution "Transforming our world: the 2030 Agenda for Sustainable Development", which set out 17 Sustainable Development Goals to be achieved by 2030. The aim of the study is to assess progress towards meeting SDG 7 "Ensure access to affordable, reliable, sustainable and modern energy for all" by individual EU countries in 2010-2021 and to determine their distance in relation to the target set for 2030. Eurostat monitors and assesses progress towards SDG 7 using seven indicators. These indicators were used to create an aggregate index. In order to limit the impact of the compensation effect on the ranking of EU countries, we applied dynamic relative taxonomy with the geometric mean to create an aggregate measure that takes into account target values for the indicators with adjusted data. The study reveals systematic progress towards reaching the EU's SDG 7 in the period 2010-2021, with differences between individual EU countries clearly decreasing. The smallest distance in relation to the target set for SDG 7 can be observed for Sweden, Denmark, Estonia, and Austria. By far the greatest progress in period 2010-2021 has been achieved by Malta, and significant for Cyprus, Latvia, Belgium, Ireland, and Poland.

The impact of human activities on blue-green water resources and quantification of water resource scarcity in the Yangtze River Basin

Under the influence of climate change and human activities, water scarcity and uneven spatial distribution have become critical factors constraining societal development and threatening ecological security. Accurately assessing changes in blue and green water resources (BW and GW) caused by human activities can reveal the actual situation of water scarcity. However, previous research often overlooked the calibration of GW and human water usage, and it rarely delved into the primary human factors leading to water scarcity and potential impact mechanisms. Therefore, based on the PCR-GLOBWB model that considers human impacts, and with reasonable calibration of B/GW and human water usage, hydrological processes were simulated under both human-influenced and natural conditions. A comprehensive assessment of the impact of human activities on BW and GW was conducted. The results show that: (1) BW and GW exhibit a spatial pattern of increasing from northwest to southeast in the basin. From 1961 to 2020, the proportion of BW showed an upward trend, while GW was decreasing; (2) The impact of human activities on changes in water resources is mainly concentrated in the midstream and dowmstream of the basin. Due to human influences, the green water flow (GWF) increased by 3-24.4 mm, and the BW volume increased by 67.2-146.4 mm. However, the green water storage (GWS) decreased by 5.6-75.4 mm; (3) The impact of human activities on blue water scarcity (BWscarcity) is significantly greater than green water scarcity (GWscarcity). The worsening of GWscarcity does not exceed 0.2, while areas where BW reaches significant deterioration (BWscarcity > 1.5) account for 1.3 %, 9.8 %, and 17 % of the upstream, midstream and downstream, respectively. (4) Irrigation activities are the main factor causing water resource scarcity. In the future, it is important to reasonably develop the potential for GW utilization and optimize BW management measures to address water resource crises.

Evaluating Losses from Water Scarcity and Benefits of Water Conservation Measures to Intercity Supply Chains in China

The severe water scarcity in China poses significant economic risks to its agriculture, energy, and manufacturing sectors, which can have a cascading effect through the supply chains. Current research has assessed water scarcity losses for global countries and Chinese provinces by using the water scarcity risk (WSR) method. However, this method involves subjective functions and parameter settings, and it fails to capture the adaptive behaviors of economies to water scarcity, compromising the reliability of quantified water scarcity loss. There is a pressing need for a new method to assess losses related to water scarcity. Here, we develop an agent-based complex network model to estimate the inter-regional and intersectoral impacts of water scarcity on both cities and basins. Subsequently, we evaluate the supply chain-wide economic benefits of four different water conservation measures as stipulated by the 14th Five-Year Plan for the Construction of a Water-Saving Society. These measures include increasing the utilization rate of recycled water in water-scarce cities, reducing the national water consumption per industrial value-added, and implementing agricultural and residential water conservation measures. Results show that direct losses constitute only 9% of the total losses from water scarcity. Approximately 37% of the losses can be attributed to interregional impacts. Among the water-scarce cities, Qingdao, Lanzhou, Jinan, and Zhengzhou pose a significant threat to China's supply chains. Agricultural water conservation yields the highest amount of water savings and economic benefits, while residential water conservation provides the highest economic benefit per unit of water saved. The results provide insights into managing water scarcity, promoting cross-regional cooperation, and mitigating economic impacts.

Envisaged methodologies for sustainable food labelling policies might worsen water scarcity

To reduce the current billions of people facing water scarcity, which is a dedicated Sustainable Development Goal (SDG) target, different actions and measures are required. This includes food labelling which accounts for water scarcity, to help consumers make informed choices when purchasing food products. The European Commission is considering the proposal of a "Sustainable food labelling framework" in the last quartal of 2023, within its ambitious Farm to Fork strategy. Implementing such a food label in the EU has a potential reach of 447 million consumers. Most prominent label candidate is its own developed PEF (Product Environmental Footprint), a tool already implemented by some retailers in the EU. However, this paper argues that the category water scarcity in the PEF has two major flaws. First, it does not account for water efficiency of a product, which is essential to solve global water stress. Second, the spatial resolution for water stress is much too coarse. The current PEF tool makes comparisons between products useless and even misleading. Its use might worsen global water scarcity, as it provides producers and consumers the wrong incentives. Urgent revision of the category water stress in the PEF is required. This can be done by using the indicators water stress and water efficiency in a complementary way, as well as using the most detailed spatial resolution science can provide.

An interval water demand prediction method to reduce uncertainty: A case study of Sichuan Province, China

Effective prediction of water demand is a prerequisite for decision makers to achieve reliable management of water supply. Currently, the research on water demand prediction focuses on point prediction method. In this study, we constructed a GA-BP-KDE hybrid interval water demand prediction model by combining non-parametric estimation and point prediction. Multiple metaheuristic algorithms were used to optimize the Back-Propagation Neural Network (BP) and Kernel Extreme Learning Machine (KELM) network structures. The performance of the water demand point prediction models was compared by the Root Mean Squared Error (RMSE), Mean Absolute Percentage Error (MAPE), Kling-Gupta Efficiency (KGE), computation time, and fitness convergence curves. The kernel density estimation method (KDE) and the normal distribution method were used to fit the distribution of errors. The probability density function with the best fitting degree was selected based on the index G. The shortest confidence interval under 95% confidence was calculated according to the asymmetry of the error distribution. We predicted the impact indicator values for 2025 using the exponential smoothing method, and obtained water demand prediction intervals for various water use sectors. The results showed that the GA-BP model was the optimal model as it exhibited the highest computational efficiency, algorithmic stability, and prediction accuracy. The three prediction intervals estimated after adjusting the KDE bandwidth parameter covered most of the sample points in the test set. The prediction intervals of the four water use sectors were evaluated as F values of 1.6845, 1.3294, 1.6237, and 1.3600, which indicates high accuracy and quality of the prediction intervals. The mixed water demand interval prediction based on GA-BP-KDE reduces the uncertainty of the point prediction results and can provide a basis for water resource management by decision makers.

Fresh water resource, scarcity, water salinity challenges and possible remedies: A review

Water is one of the natural resource due balance if our planet and the life on it have to sustain and economic development to be expected in the future. The increase in population of the world and level of wealth of humans is expected to withdraw more freshwater. However, since water is already one of the limited resources, global per capital water available surely drops and water shortage happens. Pollution of ground and surface water by dissolved salts are increasing and exacerbating this water shortage situation. The sources of these dissolved salts (such as primary and secondary salinity-causing agents) are known to change the chemical constituent of water. Once contributing factors for water scarcity are identified, future man should work on it to overcome the challenge. This paper therefore began with global water resource information and indicated different levels of scarcity to give overall clues on the situation. Salinity description, its global status, causative factors and challenges were revised before possible recommendations were indicated as indispensable solution.

Multi-model assessment identifies livestock grazing as a major contributor to variation in European Union land and water footprints

Food systems are the largest users of land and water resources worldwide. Using a multi-model approach to track food through the global trade network, we calculated the land footprint (LF) and water footprint (WF) of food consumption in the European Union (EU). We estimated the EU LF as 140-222 Mha yr^-1 and WF as 569-918 km³ yr^-1. These amounts are 5-7% of the global LF and 6-10% of the global WF of agriculture, with the EU representing 6% of the global population. We also calculated the global LF of livestock grazing, accounting only for grass eaten, to be 1,411-1,657 Mha yr^-1, and the global LF of agriculture to be 2,809-3,014 Mha yr^-1, which is about two-thirds of what the Food and Agriculture Organization Statistics (FAOSTAT) database reports. We discuss here the different methods for calculating the LF for livestock grazing, underscoring the need for a consistent methodology when monitoring the food LF and WF reduction goals set by the EU's Farm To Fork Strategy.

Methodology for a preliminary assessment of water use sustainability in industries at sub-basin level

The sustainability of industrial production, especially for highly water-demanding processes, is strictly related to water resource availability and to the dynamic interactions between natural and anthropogenic requirements over the spatial and temporal scales. The increase in industrial water demand raises the need to assess the related environmental sustainability, facing the occurrence of global and local water stress issues. The identification of reliable methodologies, based on simple indices and able to consider the impact on local water basins, may play a basilar role in water sustainability diagnosis and decision-making processes for water management and land use planning. The present work focalized on the definition of a methodology based on the calculation of indicators and indices in the view of providing a synthetic, simple, and site-specific assessment tool for industrial water cycle sustainability. The methodology was built starting from geo-referenced data on water availability and sectorial uses derived for Italian sub-basins. According to the data monthly time scale, the proposed indices allowed for an industrial water-related impacts assessment, able to take into account the seasonal variability of local resources. Three industrial factories, located in northern (SB1, SB2) and central (SB3) Italian sub-basins, were selected as case studies (CS1, CS2, CS3) to validate the methodology. The companies were directly involved and asked to provide some input data. The methodology is based on the calculation of three synthetic indexes: the Withdrawal and Consumption water Stress Index (WCSI) allowed for deriving a synthetic water stress level assessment at the sub-basin scale, also considering the spatial and temporal variations; the industrial water use sustainability assessment was achieved by calculating the Overall Factory-to-Basin Impact (OFBI) and the Internal Water Reuse (IWR) indices, which allowed a preliminary evaluation of the factories' impacts on the sub-basin water status, considering the related water uses and the overall pressures on the reference territorial context. The WCSI values highlighted significant differences between the northern sub-basins, characterised by limited water stress (WCSI_SB1 = 0.221; WCSI_SB2 = 0.047), and the central ones, more subjected to high stress (WCSI_SB3 = 0.413). The case studies CS1 and CS3 showed to exert a more significant impact on the local water resource (OFBI_CS1 = 0.18%; OFBI_CS2 = 0.192%) with respect to CS2 (OFBI = 0.002%), whereas the IWR index revealed the different company's attitude in implementing water reuse practices (IWR_CS1 = 40%; IWR_CS1 = 27%; IWR_CS1 = 99%). The proposed methodology and the indices may also contribute to assessing the effectiveness of river basin management actions to pursue sustainable development goals.

Food demand displaced by global refugee migration influences water use in already water stressed countries

Millions of people displaced by conflicts have found refuge in water-scarce countries, where their perceived effect on water availability has shaped local water security discourses. Using an annual global data set, we explain the effects of refugee migrations on the host countries' water stress through the food demand displaced by refugees and the water necessary to produce that food. The water footprint of refugee displacement increased by nearly 75% globally between 2005 and 2016. Although minimal in most countries, implications can be severe in countries already facing severe water stress. For example, refugees may have contributed up to 75 percentage points to water stress in Jordan. While water considerations should not, alone, determine trade and migration policy, we find that small changes to current international food supply flows and refugee resettlement procedures can potentially ease the effect of refugee displacement on water stress in water-vulnerable countries.

Water crisis in Iran: A system dynamics approach on water, energy, food, land and climate (WEFLC) nexus

Water scarcity is a highly complex, multifaceted and dynamic issue, which has become a severe global challenge. Water scarcity is a hyperconnected phenomenon and thus should be studied through nexus approach, however current water-energy-food (WEF) nexus underrepresents the impacts of land use change and climate change on water scarcity. Therefore, this study was investigated to expand the WEF nexus coverage of further systems, improving the accuracy of nexus models for decision-making and narrowing science-policy gap. Current study developed a water-energy-food-land-climate (WEFLC) nexus model to analyze the water scarcity. Modeling the complex behavior of water scarcity enables the analysis of the efficiency of some adaptation policies in addressing water scarcity and will provide suggestions for improving adaptation practices. The results showed that there is a substantial water supply-demand gap in study region, with an excess consumption of 62,361 million m³. Under baseline scenario, the gap between water supply and demand will enlarge, leading to water crisis in Iran as our study region. Climate change was found to be the prime cause of exacerbating water scarcity in Iran, raising evapotranspiration from 70 % to 85 % in 50 years, and considerably increasing the water demand in various sectors. In terms of policy/adaptation measure analysis, the results showed that neither supply-side nor demand-side scenarios could solely address water crisis, and mixed supply-demand side interventions can be the most effective policy to alleviate water crisis. Overall, the study suggests that water resource management practices and policies in Iran should be reevaluated to include a system thinking management approach. The results can be used as a decision support tool that can recommend suitable mitigation and adaptation strategies for water scarcity in the country.

Solutions to agricultural green water scarcity under climate change

Rain-fed agricultural systems, which solely depend on green water (i.e. soil moisture from rainfall), sustain ∼60% of global food production and are particularly vulnerable to vagaries in temperature and precipitation patterns, which are intensifying due to climate change. Here, using projections of crop water demand and green water availability under warming scenarios, we assess global agricultural green water scarcity-defined when the rainfall regime is unable to meet crop water requirements. With present-day climate conditions, food production for 890 million people is lost because of green water scarcity. Under 1.5°C and 3°C warming-the global warming projected from the current climate targets and business as usual policies-green water scarcity will affect global crop production for 1.23 and 1.45 billion people, respectively. If adaptation strategies were to be adopted to retain more green water in the soil and reduce evaporation, we find that food production loss from green water scarcity would decrease to 780 million people. Our results show that appropriate green water management strategies have the potential to adapt agriculture to green water scarcity and promote global food security.

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.

Sustainable development goals: a bibliometric analysis of literature reviews

The research in sustainable development goals (SDG) increases year by year since its approval in 2015. Typically, after a phase of exponential growth, the number of publications increases at lower rates, suggesting a consolidation process in which literature reviews become a relevant and high-evidence type of document. In this context, the aim of this study was to perform an unprecedented bibliometric analysis of literature reviews on SDG to assess the evolution and consolidation of the scientific research. Article reviews on SDG from 2015 to 2022 were retrieved from Web of Science core collection and a descriptive bibliometric analysis was performed by growth rate, research area, source, citation, and region. Mapping and cluster analysis using keyword co-occurrence, co-authorship, and bibliographic coupling were also applied. The result revealed that SDG is a fast-growing field, with a trend in the diversification of research areas. Most of the review documents were categorized in general aspects of sustainability. Technology (SDG 9) and economic growth (SDG 8) were spotted as hidden key research areas. This result is contrary to previous bibliometric studies on SDG, demonstrating the rapid evolution and change in the field. In addition, literature reviews on reduced inequalities (SDG 10), gender equality (SDG 5); oceans, seas, and marine environments (SDG 14); and peace, justice, and strong institutions (SDG 16) were revealed as research gaps. Thus, the results demonstrated that the research on SDG cannot yet be considered a consolidated area of research, as it leaves many SDG unexplored. Future research has been proposed accordingly.

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.

A systematic approach for assessing water, energy and food security during the COVID-19 pandemic: case study of Mexico

Assessing the security of the water-energy-food nexus is a topic of great importance, which allows determining the situation of each resource to implement actions for sustainable management of these resources in today's society. For this reason, a systematic procedure is proposed to evaluate the synergies of the water-energy-food nexus in a large region that is divided into subregions that allow considering their interactions. The new procedure considers the availability, accessibility and regional interdependence of resources while annexing economic and social aspects. A composite index called the WEF Global Index is developed, which involves the WEF nexus index and has nine indicators that evaluate the availability, accessibility and regional interdependence of each resource in the water-energy-food nexus. This new index considers the Gross Domestic Product per capita and the involved population. As a case study, the 32 states of Mexico were considered to assess the effects of the COVID-19 pandemic on the economy and the security of the water-energy-food nexus at the state level. For this, the composite index was evaluated in the years 2019 and 2020. The results show that from 2019 to 2020, the value of the global index increased in 13 states, in 21 states the security index of the WEF nexus increased, and in 9 states the GDP per capita index increased. On the other hand, the results indicate that in 11 states there was no improvement in the nexus security index due to the increase in water demand, which considerably affected the water availability indicator.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10668-022-02671-2.

Agricultural Adaptation to Reconcile Food Security and Water Sustainability Under Climate Change: The Case of Cereals in Iran

In this study, we simulate the crop yield and water footprint (WF) of major food crops of Iran on irrigated and rainfed croplands for the historical and the future climate. We assess the effects of three agricultural adaptation strategies to climate change in terms of potential blue water savings. We then evaluate to what extent these savings can reduce unsustainable blue WF. We find that cereal production increases under climate change in both irrigated and rainfed croplands (by 2.6-3.1 and 1.4-2.3 million t yr-1, respectively) due to increased yields (6.6%-78.7%). Simultaneously, the unit WF (m3 t-1) tends to decrease in most scenarios. However, the annual consumptive water use increases in both irrigated and rainfed croplands (by 0.3-1.8 and 0.5-1.7 billion m3 yr-1, respectively). This is most noticeable in the arid regions, where consumptive water use increases by roughly 70% under climate change. Off-season cultivation is the most effective adaptation strategy to alleviate additional pressure on blue water resources with blue water savings of 14-15 billion m3 yr-1. The second most effective is WF benchmarking, which results in blue water savings of 1.1-3.5 billion m3 yr-1. The early planting strategy is less effective but still leads to blue water savings of 1.7-1.9 billion m3 yr-1. In the same order of effectiveness, these three strategies can reduce blue water scarcity and unsustainable blue water use in Iran under current conditions. However, we find that these strategies do not mitigate water scarcity in all provinces per se, nor all months of the year.

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.

Using the WEI+ index to evaluate water scarcity at highly regulated river basins with conjunctive uses of surface and groundwater resources

This paper discusses the role and limitations of using WEI+ as a water resource management tool for highly regulated river basins, with a conjunctive use of surface and groundwater resources. By considering flow regulation by reservoirs and aquifer systems, seasonality of water availability and demand, returns from water uses and environmental flow requirements, WEI+ constitutes an improvement to existing quantitative water scarcity indexes. However, the computation of WEI+ in complex river basins systems requires detailed data on water availability and water allocation to various uses, which are hard to obtain from monitoring records. The paper describes how the combined use of hydrological and water allocation models can help to overcome data gaps in water accounting and contribute to an improved analysis of water scarcity in heterogeneous and intricate river basins. It also examines the information provided by WEI+ and by other widely used water scarcity indexes, such as the Water Stress Index and the Criticality Ratio, as well as discusses the ability of WEI+ to measure the performance of hydraulic systems, usually evaluated by parameters such as reliability, vulnerability, and resilience. The Tagus River transboundary basin was selected as case study due to massive flow regulation by multi-purpose reservoirs and significant seasonality of water availability and demand. Results show the benefits of using WEI+ to define levels of water scarcity, over other indexes. Within the Tagus River systems, high values of WEI+ are reached during the summer months in regions with intensive agriculture, denoting severe water stress conditions in most sub-basins. The analysis also reveals the strong dependence of Portugal, the downstream country, on flows from Spain, the upstream country.

Ecological Sustainability Assessment of Water Distribution for the Maintenance of Ecosystems, their Services and Biodiversity

Water provision and distribution are subject to conflicts between users worldwide, with agriculture as a major driver of discords. Water sensitive ecosystems and their services are often impaired by man-made water shortage. Nevertheless, they are not sufficiently included in sustainability or risk assessments and neglected when it comes to distribution of available water resources. The herein presented contribution to the Sustainable Development Goals Clean Water and Sanitation (SDG 6) and Life on Land (SDG 15) is the Ecological Sustainability Assessment of Water distribution (ESAW-tool). The ESAW-tool introduces a watershed sustainability assessment that evaluates the sustainability of the water supply-demand ratio on basin level, where domestic water use and the water requirements of ecosystems are considered as most important water users. An ecological risk assessment estimates potential impacts of agricultural depletion of renewable water resources on (ground)water-dependent ecosystems. The ESAW-tool works in standard GIS applications and is applicable in basins worldwide with a set of broadly available input data. The ESAW-tool is tested in the Danube river basin through combination of high-resolution hydro-agroecological model data (hydrological land surface process model PROMET and groundwater model OpenGeoSys) and further freely available data (water use, biodiversity and wetlands maps). Based on the results, measures for more sustainable water management can be deduced, such as increase of rainfed agriculture near vulnerable ecosystems or change of certain crops. The tool can support decision making of authorities from local to national level as well as private enterprises who want to improve the sustainability of their supply chains.

Water Resource Management in Hotels Using a Sustainable Balanced Scorecard

It is essential to find a balance between tourism development and sustainable consumption of water resources. To achieve this goal, a Sustainable Balanced Scorecard connected to the Sustainable Development Goals (SDG) is proposed for optimal water resource management in the hotel sector. The Scorecard is based on four perspectives: customer, internal processes, learning and improvement, and financial. The key variables were agreed on with stakeholders in the sector, and the Sustainable Balanced Scorecard was tested empirically on a sample of 70 hotels in island tourism destinations in the Macaronesia region. The results revealed that though more and more hotels have tried to implement strategies to save water, they were still a long way from reaching the international standard of 140 litres per guest night. In addition, there were significant differences concerning water consumption according to hotel category. The Sustainable Balanced Scorecard in this paper adds to the existing works about materiality in sustainability. It can also support business decision making about the SDGs and help potential investors.

Securing Land and Water for Food Production through Sustainable Land Reform: A Nexus Planning Perspective

Land and water are vital resources for sustaining rural livelihoods and are critical for rural development as they form the basis of agriculture, the main economic activity for rural communities. Nevertheless, in most developing countries, land and water resources are unevenly distributed due to historical and socio-economic imbalances, hence the need for land reform policies to address these disparities. However, redistributing land without considering the interconnectedness of land and socio-ecological systems can compound existing food and water insecurity challenges. This study used a mixed research method, integrating both quantitative and qualitative data, to develop a framework to guide policy and decision-makers to formulate coherent strategies towards sustainable land redistribution programmes and achieve the desired outcomes. The approach was vital for integrating the broad and intricate interlinkages between water, land, and environmental resources. Therefore, the framework is based on transformative and circular models for informing strategic policy decisions towards sustainable land redistribution. The focus was on South Africa’s land redistribution plans and the implications on water and food security and rural development. The developed framework is designed to ensure the sustainability of agrarian reform and rural economic development. It is framed to address land and water accessibility inequalities, promote water and food security, and enhance rural development. A sustainable land redistribution increases the adaptive capacity of rural communities to climate change, enhances their resilience, and provides pathways towards Sustainable Development Goals (SDGs).

Impact of seawater desalination and wastewater treatment on water stress levels and greenhouse gas emissions: The case of Chile

Many regions around the world are suffering from water stress, and desalinated water and recycled water are seen as alternatives for meeting the water demand. However, high energy consumption and associated greenhouse gas emissions are some of the main environmental impacts. This is notable for many arid and semi-arid countries where desalination and water recycling are considered options for ensuring water resources availability. This research presents the incorporation of the quantification of greenhouse gas emissions generated during the operation of desalination and wastewater treatment plants in the assessment of water stress levels using the water stress indicator adopted by the 2030 Agenda for Sustainable Development. Chile was chosen as a case study, as it is a country where there is a considerable difference between the availability of conventional water sources and the water demand, and the electrical grid is fed mainly by fossil fuels. The methodology proposed allows calculating the indirect greenhouse gas emissions due to electrical consumption for the operation of desalination and wastewater treatment plants, and the direct greenhouse gas emissions coming from biological processes used in wastewater treatment plants. The results showed that Chilean arid climate zones will not experience water stress in the future at the regional level, mainly because of the installation of several desalination plants by 2030. Meanwhile, recycled water from the urban sector will slightly contribute to the reduction in the level of water stress in almost all Chilean regions by 2030. Moreover, desalination and wastewater treatment plant will contribute only between 0.34% and 0.75% of total greenhouse gas emitted in Chile by 2030. Therefore, the operation of these industrial systems for facing water scarcity problems in northern and central zones of Chile is a suitable alternative because it does not generate large environmental problems.

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.

National water shortage for low to high environmental flow protection

Global freshwater biodiversity has been decreasing rapidly, requiring the restoration and maintenance of environmental flows (EFs) in streams and rivers. EFs provide many ecosystem services that benefit humans. Reserving such EFs for aquatic ecosystems, implies less renewable water availability for direct human water use such as agriculture, industry, cities and energy. Here we show that, depending on the level of EF protection, global annual renewable water availability for humans decreases between 41 and 80% compared to when not reserving EFs. With low EF protection, currently 53 countries experience different levels of water shortage, which increases to 101 countries for high EF protection. Countries will carefully have to balance the amount of water allocated to humans and the environment.

Educational Resources for Geoethical Aspects of Water Management

Global water resources are a critical value for the future of humankind. Conflicts and wars seem to rise because of such critical resources. While water-scarce countries are under extreme pressure on the long-term scale, also water-rich countries in Europe, such as Austria, face local conflicts of interest between water supply, tourism, agriculture, hydropower and ecology, for instance. Higher Education must address these conflicts and the new concepts of geoethics offer the conceptional thinking to do so. Based on educational resources for Higher Education that have been developed in the field of “Geoethics and Water Management” under the Erasmus+ co-funded project GOAL (Geoethics Outcomes and Awareness Learning), selected water-related conflicts are discussed. The cases selected for developing the educational resources are water use conflicts and geoethical aspects of hydropower plants. The educational resources include a subsequent procedure for applying them with students. Outcomes from the educational resources show that issues related to water management often create geoethical conflicts and dilemmas, and an interconnection between several Sustainable Development Goals can be established. Applying the educational resources shall enable geoscientists to contribute towards sustainable development of Earth’s future by a more holistic view.

Understanding responses to climate-related water scarcity in Africa

Water scarcity is a global challenge, yet existing responses are failing to cope with current shocks and stressors, including those attributable to climate change. In sub-Saharan Africa, the impacts of water scarcity threaten livelihoods and wellbeing across the continent and are driving a broad range of adaptive responses. This paper describes trends of water scarcity for Africa and outlines climate impacts on key water-related sectors on food systems, cities, livelihoods and wellbeing, conflict and security, economies, and ecosystems. It then uses systematic review methods, including the Global Adaptation Mapping Initiative, to analyse 240 articles and identify adaptation characteristics of planned and autonomous responses to water scarcity across Africa. The most common impact drivers responded to are drought and participation variability. The most frequently identified actors responding to water scarcity include individuals or households (32%), local government (15%) and national government (15%), while the most common types of response are behavioural and cultural (30%), technological and infrastructural (27%), ecosystem-based (25%) and institutional (18%). Most planned responses target low-income communities (31%), women (20%), and indigenous communities (13%), but very few studies target migrants, ethnic minorities or those living with disabilities. There is a lack of coordination of planned adaptation at scale across all relevant sectors and regions, and lack of legal and institutional frameworks for their operation. Most responses to water scarcity are coping and autonomous responses that showed only minor adjustments to business-as-usual water practices, suggesting limited adaptation depth. Maladaptation is associated with one or more dimension of responses in almost 20% of articles. Coordinating institutional responses, carefully planned technologies, planning for projected climate risks including extension of climate services and increased climate change literacy, and integrating indigenous knowledge will help to address identified challenges of water scarcity towards more adaptive responses across Africa.

Going beyond Global Indicators—Policy Relevant Indicators for SDG 6 Targets in the Context of Austria

Bringing forward sustainable transformation as envisioned within the Agenda 2030 requires comprehensive monitoring of the 17 Sustainable Development Goals (SDGs) formulated therein. To monitor and report progress on goal 6 on clean water and sanitation and its eight pertinent targets, 11 indicators were stipulated in an elaborated process. Yet, through continuous scientific and public scrutiny and debate several gaps and weaknesses were identified. Amongst others, these globally defined indicators are found to reflect weakly the diversity of national realities, capacities and levels of development. To translate the targets into national contexts and fully cover all aspects of the SDG 6 targets, the utilization of complementary indicators is recommended. Within this paper, following a critical appraisal of the SDG 6 indicators, possible complementary indicators are collected from literature and screened based on their quality, relevance for the national context and data availability. A deepened status quo of the SDG 6 targets and corresponding problem areas are outlined for the context of Austria, where water and sanitation infrastructure as well as regulation and governance of water bodies are widely established. Despite increasing the monitoring effort, it is concluded that complementary indicators are practicable to support coherent policy-making and ultimately contribute to the Agenda 2030’s aspiration that all countries take action.

Competition for water induced by transnational land acquisitions for agriculture

The ongoing agrarian transition from smallholder farming to large-scale commercial agriculture promoted by transnational large-scale land acquisitions (LSLAs) often aims to increase crop yields through the expansion of irrigation. LSLAs are playing an increasingly prominent role in this transition. Yet it remains unknown whether foreign LSLAs by agribusinesses target areas based on specific hydrological conditions and whether these investments compete with the water needs of existing local users. Here we combine process-based crop and hydrological modelling, agricultural statistics, and georeferenced information on individual transnational LSLAs to evaluate emergence of water scarcity associated with LSLAs. While conditions of blue water scarcity already existed prior to land acquisitions, these deals substantially exacerbate blue water scarcity through both the adoption of water-intensive crops and the expansion of irrigated cultivation. These effects lead to new rival water uses in 105 of the 160 studied LSLAs (67% of the acquired land). Combined with our findings that investors target land with preferential access to surface and groundwater resources to support irrigation, this suggests that LSLAs often appropriate water resources to the detriment of local users.

Water scarcity associated with large-scale land acquisitions is exacerbated by adoption of water-intensive crops and expansion of irrigation, which in turn increases rival water uses.

SDG indicator 6.4.1 "change in water use efficiency over time": Methodological flaws and suggestions for improvement

Sustainable Development Goal indicator 6.4.1 is defined as the change in water use efficiency over time and measured as the change in the ratio of gross economic value added by irrigated agriculture, industry and the services sector to the volume of water withdrawn over time. The rationale behind this indicator is to decouple a country's economic growth from its water use. Yet, this unwittingly results in an economic distortion of the water balance, favouring increased water withdrawal in service of higher water-use efficiency, at the expense of environmental sustainability. This paper discusses three methodological flaws. First, aggregation of only economic values across all sectors ignores social and environmental values and is very sensitive to changes in the relative water use by agriculture versus industry and services. Second, the economic value derived from agriculture and from imports cannot in fact be decoupled from agricultural water use. Third, the indicator completely ignores the effects of diminished return flows to the environment due to increased re-use of water. A novel alternative, disaggregated WUE approach is therefore proposed, which links water consumption to the water balance. It is defined as the economic value of irrigated and rainfed agriculture combined with water consumption (ET_a) by rainfed and irrigated agriculture per area based on earth observation data. It is measured as the change in the ratio of gross economic value added by irrigated and rainfed agriculture to the volume of water consumed by rainfed and irrigated agriculture over time. This approach is more consistent and objective, while being methodologically, hydrologically and environmentally sound. It acknowledges the coupling of economic growth and water depletion, and the need to strike a balance between opportunities for economic growth and environmental sustainability. This better serves the full breadth of the water and sanitation goal as defined in SDG 6.

Assessing SDG indicator 6.4.2 'level of water stress' at major basins level

This paper describes a method to disaggregate indicator 6.4.2 (level of water stress) by major river basins. The analysis was performed using the GlobWat soil water balance model and global geospatial data consistent with national statistics published in AQUASTAT, the FAO's global information system on water and agriculture. When a river basin spans across more than one country, the water stress calculated by country can be very different from that calculated by the river basin as the counting of the renewable freshwater resources from one country to another is highly dependent on the official agreement and treaties that regulate the flow of those resources between countries. This problem is solved hydrologically once the accounting of the water resources is done on the major river basin as a whole. The disaggregation by the river basin allows the identification of hotspots where actions should be prioritised and reveals that the area affected by a high or critical water stress spans across all continents with the exception of Oceania. It also offers the possibility of an analysis of freshwater withdrawals by sector, which may become crucial for the definition of water management policies in the context of the economic development of a country.

The number of people exposed to water stress in relation to how much water is reserved for the environment: a global modelling study

BACKGROUND

Increasing human demand for water and changes in water availability due to climate change threatens water security worldwide. Additionally, exploitation of water resources induces stress on freshwater environments, leading to biodiversity loss and reduced ecosystem services. We aimed to conduct a spatially detailed assessment of global human water stress for low to high environmental flow (EF) protection.

METHODS

In this modelling study, we used the LISFLOOD model to generate daily natural flows without anthropogenic water use for 1980-2018. On the basis of these flows, we selected three EF methods (EF with high ecological protection [EF_PROT], EF with minimum flow requirements [EF_MIN], and variable monthly flow [EF_VMF]) to calculate monthly EFs. We assessed monthly consumptive water use for industry, agricultural crops, livestock, municipalities, and energy production for 2010. We then estimated the corresponding number of people under water stress per month on a global and national level using a spatially detailed population database for 2010.

FINDINGS

We estimate that 3·2 billion (EF_PROT), 2·4 billion (EF_VMF), and 2·2 billion (EF_MIN) people lived under water stress for at least 1 month per year, corresponding to 46%, 35%, and 32% of the world's population in 2010, respectively. Around 80% of people living under water stress lived in Asia; in particular, India, Pakistan, and northeast China. Compared with EF_MIN, imposing EF_PROT globally would have put between 710 million (March) to 1 billion (June) additional people under water stress on a monthly basis, whereas this would have been 72 million (August) to 218 million (April) additional people if EF_VMF were imposed.

INTERPRETATION

Ensuring high ecological protection would put nearly half of the world's population (3·2 billion people) under water stress for at least 1 month per year. Policy makers and water managers have to make an important trade-off when allocating limited water resources between direct human needs and the environment. A better understanding of local ecosystem needs is crucial to alleviating current and future human water stress, while sustaining healthy ecosystems.

FUNDING

None.

Identification of Potential Surface Water Resources for Inland Aquaculture from Sentinel-2 Images of the Rwenzori Region of Uganda

Aquaculture has the potential to sustainably meet the growing demand for animal protein. The availability of water is essential for aquaculture development, but there is no knowledge about the potential inland water resources of the Rwenzori region of Uganda. Though remote sensing is popularly utilized during studies involving various aspects of surface water, it has never been employed in mapping inland water bodies of Uganda. In this study, we assessed the efficiency of seven remote-sensing derived water index methods to map the available surface water resources in the Rwenzori region using moderate resolution Sentinel 2A/B imagery. From the four targeted sites, the Automated Water Extraction Index for urban areas (AWEInsh) and shadow removal (AWEIsh) were the best at identifying inland water bodies in the region. Both AWEIsh and AWEInsh consistently had the highest overall accuracy (OA) and kappa (OA > 90%, kappa > 0.8 in sites 1 and 2; OA > 84.9%, kappa > 0.61 in sites 3 and 4), as well as the lowest omission errors in all sites. AWEI was able to suppress classification noise from shadows and other non-water dark surfaces. However, none of the seven water indices used during this study was able to efficiently extract narrow water bodies such as streams. This was due to a combination of factors like the presence of terrain shadows, a dense vegetation cover, and the image resolution. Nonetheless, AWEI can efficiently identify other surface water resources such as crater lakes and rivers/streams that are potentially suitable for aquaculture from moderate resolution Sentinel 2A/B imagery.

Territorial and Sustainable Healthy Diets

The rapid changes that societies have gone through in the last few decades have led to the increase in the prevalence of malnutrition in all its forms and to the degradation of natural resources and the environment. The change in the dietary habits and production systems are responsible for much of this change. Some territorial diets have been shown as potentially capable of reversing these trends by positively contributing to the health of people and the environment such as the Mediterranean Diet and the New Nordic Diet. In this paper, we review the contribution of these 2 diets to health and nutrition and to environmental, sociocultural, and economic sustainability proposing pertinent indicators. Learning from a culturally established diet and a constructed one, tradeoff could be reached to ensure better health and sustainability outcomes. Strong factors for achieving this goal lie in building on the sociocultural appropriation of diets, having the proper tools and indicators, investing in cross-sector collaboration and policy coherence, and having the necessary political support to push the agenda of sustainability forward.

Global assessment of future sectoral water scarcity under adaptive inner-basin water allocation measures

Water scarcity has become a major threat to sustainable development under climate change. To reduce the population exposure to water scarcity and improve universal access to safe drinking water are important targets of the Sustainable Development Goal (SDG) 6 in the near future. This study aims to examine the potential of applying adaptive inner-basin water allocation measures (AIWAM), which were not explicitly considered in previous studies, for mitigating water scarcity in the future period (2020-2050). By incorporating AIWAM in water scarcity assessment, nonagricultural water uses are assumed to have high priority over agricultural water use and thus would receive more water supply. Results show that global water deficit is projected to be ~3241.9 km³/yr in 2050, and severe water scarcity is mainly found in arid and semi-arid regions, e.g. Western US, Northern China, and the Middle East. Future warming climate and socioeconomic development tend to aggravate global water scarcity, particularly in Northern Africa, Central Asia, and the Middle East. The application of AIWAM could significantly mitigate water scarcity for nonagricultural sectors by leading to a decrease of global population subject to water scarcity by 12% in 2050 when compared to that without AIWAM. However, this is at the cost of reducing water availability for agricultural sector in the upstream areas, resulting in an increase of global irrigated cropland exposed to water scarcity by 6%. Nevertheless, AIWAM provides a useful scenario that helps design strategies for reducing future population exposure to water scarcity, particularly in densely populated basins and regions. Our findings highlight increasing water use competition across sectors between upstream and downstream areas, and the results provide useful information to develop adaptation strategies towards sustainable water management.

Which diet has the lower water footprint in Mediterranean countries?

The Mediterranean region is increasingly water scarce, with the food system being the largest driver of water use. We calculate the water resources related to food consumption in nine major Mediterranean countries, by means of the water footprint (WF), for the existing situation (period 2011-2013) as well as the Mediterranean and EAT-Lancet diets. We account for different food intake requirements according to gender and six age groups. These nine countries - Spain, France, Italy, Greece, Turkey, Egypt, Tunisia, Algeria and Morocco - represent 88% of the population of all countries bordering the Mediterranean. As first major observation, we find that the EAT-Lancet diet, a scientifically optimised diet for both nutrition and certain environmental indicators, requires less water resources than the Mediterranean diet, a culturally accepted diet within the region. In terms of water resources use, adherence to the former is thus more beneficial than adherence to the latter. As second major observation, we find that the EAT-Lancet diet reduces the current WF for all nations consistently, within the range -17% to -48%, whereas the Mediterranean diet reduces the WF of the European countries, Turkey, Egypt and Morocco within the range of -4% to -35%. For the Maghreb countries Tunisia and Algeria, the Mediterranean diet WF is slightly higher compared to the current WF and the proportions of food product groups differ. Such dietary shifts would be important parts of the solution to obtain the sustainable use of water resources in Mediterranean countries.

A quantitative approach to resource effectiveness assessment: Application in the Urmia Lake Basin

This paper aims to present a new quantitative systematic approach to evaluate the effectiveness of utilizing and allocating resources based on the concept of "Work" in physics. This method is examined in the Urmia Lake Basin (ULB), shrinking of which has threatened the life of about five million inhabitants and ecosystem biodiversity. In the proposed approach, the role of three types of financial, human, and environmental resources in the development process is evaluated quantitatively, and they have been compared in two periods before and after the severe reduction of the lake water volume. Results show that although financial resources have increased by 1.9 times in the second period, the effectiveness of the development process has decreased. Therefore, the resources have not been utilized properly in a direction compatible with sustainable development strategies. Additionally, the improperly-spent financial resources on the development projects especially in the second period have had a more destructive role than the human and environmental resources in the ULB crisis.

Indicators and Recommendations for Assessing Sustainable Healthy Diets

Research coupling human nutrition and sustainability concerns is a rapidly developing field, which is essential to guide governments' policies. This critical and comprehensive review analyzes indicators and approaches to "sustainable healthy diets" published in the literature since this discipline's emergence a few years ago, identifying robust gauges and highlighting the flaws of the most commonly used models. The reviewed studies largely focus on one or two domains such as greenhouse gas emissions or water use, while overlooking potential impact shifts to other sectors or resources. The present study covers a comprehensive set of indicators from the health, environmental and socio-economic viewpoints. This assessment concludes that in order to identify the best food option in sustainability assessments and nutrition analysis of diets, some aspects such as the classification and disaggregation of food groups, the impacts of the rates of local food consumption and seasonality, preservation methods, agrobiodiversity and organic food and different production systems, together with consequences for low-income countries, require further analysis and consideration.

Unraveling the effect of inter-basin water transfer on reducing water scarcity and its inequality in China

Securing water supply in the face of increasing water scarcity is one important challenge faced by humanity in sustainable development. Inter-basin water transfer is widely applied to provide water supply security in regions where water demand exceeds water availability. However, the effect of inter-basin water transfer on alleviating water scarcity and its inequality is poorly understood especially at the national scale. Based on a newly compiled database of inter-basin water transfer projects in China, here we report a first national assessment of their effect on securing water supply in different basins. We developed a number of indices to facilitate quantifying the effect of water transfer on water scarcity and its inequality. The capacity of inter-basin transfer projects has been steadily increased, which achieved ~48.5 billion m³ yr^-1 by 2016 (equivalent to ~8% of the national water use). The results indicate that water transfer has impacted water supply of 43 sub-basins out of a total of 76 sub-basins, but it hardly changes a basin's water scarcity level (e.g., from water scarcity to low water scarcity). Approximately three quarters of people in China are affected by water transfer. More than a half of the national population (705 million) benefit from alleviated water scarcity, leading to the inequality coefficient reduced from 0.64 under natural water availability condition to 0.59 considering water transfer in 2016. However, 357 million people in water transfer source basins are subject to increased water scarcity, in which ~21% are from water stressed sub-basins. This study reveals for the first time water transfer induced water scarcity and inequality change across sub-basins in China, and highlights the challenges to secure water supply across basins.

Understanding the Spatial-Temporal Changes of Oasis Farmland in the Tarim River Basin from the Perspective of Agricultural Water Footprint

The Tarim River Basin in China has predominantly assumed the task of commodity cotton and other high water-intensive crop production in recent years. The spatial matching status of agricultural water and land resources is a prerequisite for local economic development. This paper provides an insight into the spatiotemporal variation trends of agricultural production water footprint and oasis farmland in the Tarim River Basin. The degree of spatial mismatching between oasis farmland and crop production water footprints studied in this paper found how the crop water footprint affected the change in oasis farmland area by sensitivity analysis. Time series data covering the period of 1990–2015 were used for the study. The results showed that the annual variation of crop production water footprint and oasis farmland area have experienced upward trends in Tarim River Basin. The blue water makes the largest contribution to the components of the crop production water footprint in each district (all exceeded 77%). The crop production water footprint and oasis farmland area tend to aggregate towards the eastern region. The level of spatial mismatch between the blue water footprint and farmland area fluctuated during the study period, but it was gradually remedied after 2000, while the spatial mismatch between green water footprint and farmland area gradually worsened. The number of districts with mid and high sensitivity to changes in blue water footprint continuously increased during 1990–2005, which revealed that the change in blue water footprint has an increasing influence on oasis farmland. The results can provide operable recommendations for efficient use of water resources, maintaining oasis suitable farmland scale and agricultural sustainable development in the Tarim River Basin.

The scarcity-weighted water footprint provides unreliable water sustainability scoring

To evaluate the environmental sustainability of blue water use or the blue water footprint (WF) of a product, organisation, geographical entity or a diet, two well-established indicators are generally applied: water efficiency and blue water stress. In recent years, the Life Cycle Assessment (LCA) community has developed, used and promoted the indicator scarcity-weighted WF, which aims to grasp both blue water use and blue water stress in one indicator. This indicator is now recommended in an ISO document on water footprinting and many scholars have used associated scarcity-weighted water use indicators. However, questions on its physical meaning and its ability to correctly evaluate water sustainability have emerged. Here, we analyse for global irrigated wheat production to what extend the scarcity-weighted WF addresses blue water stress and water efficiency. We observe inconsistent results, as a significant proportion of unsustainably produced irrigated wheat has better scarcity-weighted WF scores as compared to sustainably produced irrigated wheat. Using the scarcity-weighted WF or scarcity-weighted water use for policy-making including product labelling, punishes some farmers producing their wheat in a water-sustainable way and promotes some farmers producing wheat unsustainably. Applying the scarcity-weighted WF indicator thereby is contraproductive in reaching the Sustainable Development Goal (SDG) target 6.4 on reducing water stress. In line with the specifications of this SDG target, to evaluate the sustainability of blue water use or the blue WF, the two indicators water stress and water efficiency should be used separately, in a complementary way.

Water footprint coupled economic impact assessment for maize production in China

Nowadays, agricultural production places an enormous burden on freshwater resources, and the environmental external cost caused by the restoration of water quality degradation has attracted great attention. Maize is regarded as one of the world's major food security crops, and China is the second-largest maize producer. Thus, this study conducts an impact-oriented water footprint coupled economic impact assessment to quantify the water-related environmental impacts and economic burden caused by China's maize production from 2008 to 2017. Results show that the overall damage to human health and ecosystem quality of China's maize production in 2017 were 4.32 × 10⁴ DALY and 4.62 × 10³ Species·yr, respectively. The total economic cost was $ 2.15 × 10¹¹, which included an internal cost of $ 5.99 × 10¹⁰ and external cost of $ 1.55 × 10¹¹. Key factor analysis demonstrates that diesel and fertilizer production dominated the reduction in ecological and external cost burdens. Direct water consumption and labor cost played leading roles in human health and internal cost, respectively. The spatiotemporal variation assessment indicates that Inner Mongolia and Heilongjiang were the hotspots for water footprint and economic impact assessment results after considering the yield factor. The national average water footprint and economic impact caused by producing 1 ton of maize showed an upward trend from 2008 to 2015, however, a significant decline transpired later. Overall, improving the resource efficiency (i.e., diesel and freshwater), scientific application of fertilizer and reducing labor input can further lessen the water footprint and economic impact of maize production. Developing the social environment can also generate indirect environmental and economic benefits to China's maize production.

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.

An analytical framework to assess SDG targets within the context of WEFE nexus in the Mediterranean region

Understanding the complex relationships amongst Water, Energy, Food and Ecosystems (WEFE nexus) together with the achievement of Sustainable Development Goals (SDGs) is critical for the development of a sustainable and secure future in the Mediterranean area. In this study, we analysed 29 case studies across the Mediterranean region which describe potential success stories for the implementation of good nexus practices. We developed an analytical framework for investigating the impacts on 15 SDG targets and we also explicitly quantified the magnitude of interconnection of nexus pillars with SDGs. Our findings showed that renewable energies have a predominant role on sustainability. Moreover, to achieve the highest positive impacts on economy, environment and society, it is necessary to ensure that both people and ecosystems benefit from a minimum amount of goods/qualities as expected by specific targets like SDG 6.1-4 (clean water and sanitation) and 15.1-3 (life on land), as well as 7.2-3 (affordable and clean energy) that are strongly linked with 13.1 (climate action). We showed also that the strongest interconections between SDG and WEFE are present for the categories of renewable energy system (RED and REW). However, the analysis showed that there is a tendency to focus on a specific sector (e.g. agriculture) and that the good nexus practices implementation is not enough to understand the achievement and progress towards the SDGs. For that reason, we recommended that a more holistic nexus approach including end of supply chain options should be systematically integrated into the project design or evaluation.

Water-related challenges in nexus governance for sustainable development: Insights from the city of Arequipa, Peru

Peru has one of the fastest-growing economies in Latin America, but there are concerns regarding how long this can be sustained. Negative environmental impacts are increasing due to the pressures of a growing urban population and competition for natural resources. This study explores stakeholder perceptions linked to nexus governance in the context of integrated management of natural resources, particularly water, and the environmental, socio-economic and governance challenges constraining the achievement of UN Sustainable Development Goals (SDGs). Our analysis focused on the urban and rural areas associated with the city of Arequipa, an economically dynamic region subject to extreme levels of water stress. Face-to-face interviews with key informants were conducted to identify mechanisms that have enhanced successful multi-sectoral collaboration, and to assess challenges in promoting sustainable economic development. A workshop prioritised the identified challenges and an online survey was then used to assess stakeholder interest in and influence over nexus governance of water with other natural resources. Stakeholder mapping revealed a complex network of actors involved in nexus governance, where successful collaboration could be promoted through formal and informal mechanisms, including exemplar policies and initiatives across sectors and actors. Shared visions between stakeholders were identified as well as contradictory priorities relating to the sustainable management of natural resources. A key finding that emerged was the need to promote adaptation in water and land management (SDG 6) due to perceived impacts of extreme climate events (SDG 13), urban population growth (SDG 11), and increased sectoral water demands. This situation in combination with poor governance and lack of planning has exposed the vulnerability of Arequipa water supply system to future shocks. Urgent action will be needed to raise stakeholder awareness, strengthen governance and enforcement, and agree on a collective vision for integrated land and water planning if the SDGs are to be achieved.