Limits to the world's green water resources for food, feed, fiber, timber, and bioenergy

US Corn Belt enhances regional precipitation recycling

Precipitation recycling, where evapotranspiration (ET) from the land surface contributes to precipitation within the same region, is a critical component of the water cycle. This process is especially important for the US Corn Belt, where extensive cropland expansions and irrigation activities have significantly transformed the landscape and affected the regional climate. Previous studies investigating precipitation recycling typically relied on analytical models with simplifying assumptions, overlooking the complex interactions between groundwater hydrology and agricultural management. In this study, we use high-resolution climate models coupled with an explicit water vapor tracer algorithm to quantify the impacts of shallow groundwater, dynamic crop growth, and irrigation on regional precipitation recycling in the US Corn Belt. We find that these coupled groundwater-crop-irrigation processes reduce surface temperatures and increase the growing season precipitation. The increase in precipitation is attributed to a significant enhancement of the precipitation recycling ratio from 14 to 18%. This enhanced precipitation recycling is stronger in a dry year than normal and wet years, depending on both large-scale moisture transport and local ET. Our study underscores the critical role of groundwater hydrology and agricultural management in altering the regional water cycle, with important implications for regional climate predictions and food and water security.

Advancing water security in Africa with new high-resolution discharge data

VegDischarge v1, which covers over 64,000 river segments in Africa, is a natural river discharge dataset produced by coupled modeling; the agro-hydrologic VegET model and the mizuRoute routing model for the period 2001-2021. Using remote sensing data and hydrological modeling system, the 1-km runoff field simulated by VegET, was routed with mizuRoute. Performance metrics show strong model reliability, with R² of 0.5-0.9, NSE of 0.6-0.9, and KGE of 0.5-0.8 at the continental scale. The total average annual discharge for Africa is quantified at 3271.4 km³·year-1, with contributions to oceanic basins: 1000.0 km³·year-1 to the North Atlantic, primarily from the Senegal, Gambia, Volta, and Niger Rivers; 1327.2 km³·year-1 to the South Atlantic, largely from the Congo River; 214.7 km³·year-1 to the Mediterranean Sea, predominantly from the Nile River; and 729.4 km³·year-1 to the Indian Ocean, with inputs from rivers such as the Zambezi. The dataset is valuable for stakeholders and researchers to understand water availability, its temporal and spatial variations that affect water-related infrastructure planning, sustainable resource allocation, and the development of climate resilience strategies.

Blue valorization of lignin-derived monomers via reprogramming marine bacterium Roseovarius nubinhibens

Biological valorization of lignin, the second most abundant biopolymer on Earth, is an indispensable sector to build a circular economy and net-zero future. However, lignin is recalcitrant to bioupcycling, demanding innovative solutions. We report here the biological valorization of lignin-derived aromatic carbon to value-added chemicals without requesting extra organic carbon and freshwater via reprogramming the marine Roseobacter clade bacterium Roseovarius nubinhibens. We discovered the unusual advantages of this strain for the oxidation of lignin monomers and implemented a CRISPR interference (CRISPRi) system with the lacI-Ptrc inducible module, nuclease-deactivated Cas9, and programmable gRNAs. This is the first CRISPR-based regulatory system in R. nubinhibens, enabling precise and efficient repression of genes of interest. By deploying the customized CRISPRi, we reprogrammed the carbon flux from a lignin monomer, 4-hydroxybenzoate, to achieve the maximum production of protocatechuate, a pharmaceutical compound with antibacterial, antioxidant, and anticancer properties, with minimal carbon to maintain cell growth and drive biocatalysis. As a result, we achieved a 4.89-fold increase in protocatechuate yield with a dual-targeting CRISPRi system, and the system was demonstrated with real seawater. Our work underscores the power of CRISPRi in exploiting novel microbial chassis and will accelerate the development of marine synthetic biology. Meanwhile, the introduction of a new-to-the-field lineage of marine bacteria unveils the potential of blue biotechnology leveraging resources from the ocean.IMPORTANCEOne often overlooked sector in carbon-conservative biotechnology is the water resource that sustains these enabling technologies. Similar to the "food-versus-fuel" debate, the competition of freshwater between human demands and bioproduction is another controversial issue, especially under global water scarcity. Here, we bring a new-to-the-field lineage of marine bacteria with unusual advantages to the stage of engineering biology for simultaneous carbon and water conservation. We report the valorization of lignin monomers to pharmaceutical compounds without requesting extra organic substrate (e.g., glucose) or freshwater by reprogramming the marine bacterium Roseovarius nubinhibens with a multiplex CRISPR interference system. Beyond the blue lignin valorization, we present a proof-of-principle of leveraging marine bacteria and engineering biology for a sustainable future.

Global impacts of heat and water stress on food production and severe food insecurity

In contrast to most integrated assessment models, with limited transparency on damage functions and recursive temporal dynamics, we use a unique large-dimensional computational global climate and trade model, GTAP-DynW, to directly project the possible intertemporal impacts of water and heat stress on global food supply and food security to 2050. The GTAP-DynW model uses GTAP production and trade data for 141 countries and regions, with varying water and heat stress baselines, and results are aggregated into 30 countries/regions and 30 commodity sectors. Blue water stress projections are drawn from WRI source material and a GTAP-Water database to incorporate dynamic changes in water resources and their availability in agricultural production and international trade, thus providing a more general measure for severe food insecurity from water and heat stress damages with global warming. Findings are presented for three representative concentration pathways: RCP4.5-SSP2, RCP8.5-SPP2, and RCP8.5-SSP3 (population growth only for SSPs) and project: (a) substantial declines, as measured by GCal, in global food production of some 6%, 10%, and 14% to 2050 and (b) the number of additional people with severe food insecurity by 2050, correspondingly, increases by 556 million, 935 million, and 1.36 billion compared to the 2020 model baseline.

The Andes-Amazon-Atlantic pathway: A foundational hydroclimate system for social-ecological system sustainability

The Amazon River Basin's extraordinary social-ecological system is sustained by various water phases, fluxes, and stores that are interconnected across the tropical Andes mountains, Amazon lowlands, and Atlantic Ocean. This "Andes-Amazon-Atlantic" (AAA) pathway is a complex hydroclimatic system linked by the regional water cycle through atmospheric circulation and continental hydrology. Here, we aim to articulate the AAA hydroclimate pathway as a foundational system for research, management, conservation, and governance of aquatic systems of the Amazon Basin. We identify and describe the AAA pathway as an interdependent, multidirectional, and multiscale hydroclimate system. We then present an assessment of recent (1981 to 2020) changes in the AAA pathway, primarily reflecting an acceleration in the rates of hydrologic fluxes (i.e., water cycle intensification). We discuss how the changing AAA pathway orchestrates and impacts social-ecological systems. We conclude with four recommendations for the sustainability of the AAA pathway in ongoing research, management, conservation, and governance.

Assessing ecological risks and spatial distribution of potentially toxic elements in soils from anthropized environments in a watershed at the caatinga-Atlantic forest ecotone in Brazil

Understanding the processes of mobility and availability of potentially toxic elements in soil is crucial for informed decision-making in the development of public policies aimed at minimizing environmental impacts. Monitoring, in combination with the determination of natural concentrations, can provide effective tools for controlling pollution sources. In this study, enrichment, pollution, and ecological risk indices were used for some potentially toxic elements in an anthropogenically influenced watershed in southwestern Bahia, Brazil. The study involved 63 composite surface soil samples collected from areas with natural forest, crops, pastures, and urbanization. The samples were analyzed for fertility and particle size. Metal extraction followed the EPA 3051A method, and element determination was carried out via ICP-OES. The soils in the Verruga River watershed exhibit a high variability in fertility and granulometric attributes. The Kruskal-Wallis test at a 5% significance level was employed to assess the impact of land management on the availability of elements (As, Co and Pb), while Spearman's correlation, along with hierarchical clustering analysis, was used to comprehend element dynamics. Geostatistics were applied to identify pollution hotspots. Consequently, it became evident that potentially toxic elements can accumulate in the soil depending on land use and management practices (As, Co, and Pb), as well as the weathering process linked to the type of source material, such as diamictite deposits (Ni and Co). Soils in the Verruga River watershed qualify as having minimal enrichment, low pollution levels, and individual ecological risk concerning Cd. The percentage of samples enriched with Cu, As, Zn, and Cd exceeded 67%, with agricultural activities being the primary source of pollution. Meanwhile, in pasture and urban areas, Co and Pb were notably prominent, respectively.

Carbon reduction and water saving potentials for growing corrugated boxes for express delivery services in China

Corrugated packaging for express grew by 90 times to 16.5 Mt y-1 in China, where 81% of recent global express delivery growth occurred. However, the environmental impacts of production, usage, disposal, and recycling of corrugated boxes under the entire supply chain remain unclear. Here, we estimate the magnitudes, drivers, and mitigation potentials of cradle-to-grave life-cycle carbon footprint (CF) and three colors of water footprints (WFs) for corrugated cardboard packaging in China. Over 2007 to 2021, CF, blue and gray WFs per unit package decreased by 45%, 60%, and 84%, respectively, while green WF increased by 23% with growing imports of virgin pulp and China's waste ban. National total CF and WFs were 21 to 102 folded with the scale effects. Only a combination of the supply chain reconstruction, lighter single-piece packaging, and increased recycling rate can possibly reduce the environmental footprints by 24 to 44% by 2035.

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.

Water footprints and crop water use of 175 individual crops for 1990-2019 simulated with a global crop model

The water footprint of a crop (WF) is a common metric for assessing agricultural water consumption and productivity. To provide an update and methodological enhancement of existing WF datasets, we apply a global process-based crop model to quantify consumptive WFs of 175 individual crops at a 5 arcminute resolution over the 1990-2019 period. This model simulates the daily crop growth and vertical water balance considering local environmental conditions, crop characteristics, and farm management. We partition WFs into green (water from precipitation) and blue (from irrigation or capillary rise), and differentiate between rainfed and irrigated production systems. The outputs include gridded datasets and national averages for unit water footprints (expressed in m3 t-1 yr-1), water footprints of production (m3 yr-1), and crop water use (mm yr-1). We compare our estimates to other global studies covering different historical periods and methodological approaches. Provided outputs can offer insights into spatial and temporal patterns of agricultural water consumption and serve as inputs for further virtual water trade studies, life cycle and water footprint assessments.

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.

Ecological impact assessment of green virtual water flow in inter-provincial crop commutation within China

Green water is crucial for to regional ecological sustainability. Currently, there is a lack of research on the impact of crop green water communication on the regional ecology in China. The ecological impact index (EII) and integrated ecological water supply (IES) were proposed to comprehensively evaluate the regional ecological impact of the green virtual water flow (GVWF) of crops. Based on the principle of trade cost minimization, this study simulated the inter-provincial crop commutation within China during 2010-2019 by assigning weights to production, demand, and transportation costs, and analyzed the impact of crop communication on regional ecology. The results showed that multi-year average GVWF among provinces was 216.45 Gm3, accounting for 33.7 % of the total green water footprint of crops. The ecological impact of GVWF varies among provinces and years. The EII values in Beijing, Shanghai, and Jiangsu were all >100, whereas it was <1 in Yunnan and Xizang. Regional management policies for water resources, ecology, and economic development should be formulated taking into account the IES and EII jointly. It is recommended to increase the export of green virtual water of crops and expand the ecological area while ensuring the utilization rate of green water in regions with higher EII values, such as Guangxi and Yunnan. In the future, it is important for district managers to prioritize the quality of ecological development and protect ecological areas from erosion while pursuing urban development. This study innovatively evaluated the ecological impact of crop communication in different regions, which has guiding significance for the trade management in the ecologically water-deficient areas.

WITHDRAWN: Unlimited possibilities to use Сladophora (Chlorophyta, Ulvophyceae, Cladophorales) biomass in agriculture and aquaculture with profit for the environment and humanity

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/policies/article-withdrawal). This article has been withdrawn at the request of the Publisher for legal reasons related to Elsevier's policy on Geographic Sanctions (https://www.elsevier.com/about/policies/trade-sanctions).

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.

Advancing water footprint assessments: Combining the impacts of water pollution and scarcity

Several water footprint indicators have been developed to curb freshwater stress. Volumetric footprints support water allocation decisions and strive to increase water productivity in all sectors. In contrast, impact-oriented footprints are used to minimize the impacts of water use on human health, ecosystems, and freshwater resources. Efforts to combine both perspectives in a harmonized framework have been undertaken, but common challenges remain, such as pollution and ecosystems impacts modelling. To address these knowledge gaps, we build upon a water footprint assessment framework proposed at conceptual level to expand and operationalize relevant features. We propose two regionalized indicators, namely the water biodiversity footprint and the water resource footprint, that aggregate all impacts from toxic chemicals, nutrients, and water scarcity. The first impact indicator represents the impacts on freshwater ecosystems. The second one models the competition for freshwater resources and its consequences on freshwater availability. As part of the framework, we complement the two indicators with a sustainability assessment representing the levels above which ecological and human freshwater needs are no longer sustained. We test our approach assessing the sustainability of water use in the European Union in 2010. Water stress hampers 15 % of domestic, agricultural and industrial water demand, mainly due to irrigation and pesticide emissions in southern Europe. Moreover, damage to the freshwater ecosystems is widespread and mostly resulting from chemical emissions from industry. Approximately 5 % of the area is exceeding the regional sustainability limits for ecosystems and human water requirements altogether. Concerted efforts from all sectors are needed to reduce the impacts of emissions and water consumption under the sustainability limits. These advances are considered an important step toward the harmonization of volumetric and impact-oriented approaches to achieve consistent and holistic water footprinting as well as contributing to strengthen the policy relevance of water footprint assessments.

Water footprint and virtual water flows from the Global South: Foundations for sustainable agriculture in periods of drought

Freshwater availability has decreased alarmingly worldwide, with agriculture playing a vital role in this trend. The assessment of the agricultural water footprint (WF_agricultural) and virtual water flows (VWF) is fundamental not only in local water resources management and protection, but also in our understanding of the synergies between local water consumption and global markets. Thus, the WF_agricultural - broken down into its components (blue, green, and gray) - of the leading 21 crops (grouped in fruit, legumes, cereals, and vegetables), grown in four basins with the most significant agricultural activity in central Chile was determined, estimated in two consecutive years 2017-2018. In addition, due to their great importance in exports, VWFs were assessed, establishing connections according to their origins and destinations. The results show that the green and gray water footprints increased significantly in the south-central basins, while blue water consumption increased in the basins of the central zone, reflecting an evident WF_agricultural transition in accord with latitude and climate conditions. Furthermore, VWF showed an annual increase of 44 %, in about 116 destinations, with Asia, Europe, and North America being the preferred destinations, with annual variations of VWF_{blue- gray} associated with increases in exports of apples, cherries, grapes, blueberries, and walnuts, market preferences and growing areas. The present study is an initial step toward sustainable agriculture in a commodity exporting country, one that is relevant in the exploitation of virtual water yet faces severe water deficit problems, distribution, and local water policies. Therefore, contributing to encouraging the efficiency and value of water in the process of a new institutional framework.

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.

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.

Fouling in reverse osmosis membranes: monitoring, characterization, mitigation strategies and future directions

Water scarcity has been a global challenge for many countries over the past decades, and as a result, reverse osmosis (RO) has emerged as a promising and cost-effective tool for water desalination and wastewater remediation. Currently, RO accounts for >65% of the worldwide desalination capacity; however, membrane fouling is a major issue in RO processes. Fouling reduces the membrane's lifespan and permeability, while also increases the operating pressure and chemical cleaning frequency. Overall, fouling reduces the quality and quantity of desalinated water, and thus hinders the sustainable application of RO membranes by disturbing its efficacy and economic aspects. Fouling arises from various physicochemical interactions between water pollutants and membrane materials leading to foulants' accumulation onto the membrane surfaces and/or inside the membrane pores. The current review illustrates the main types of particulates, organic, inorganic and biological foulants, along with the major factors affecting its formation and development. Moreover, the currently used monitoring methods, characterization techniques and the potential mitigation strategies of membrane fouling are reviewed. Further, the still-faced challenges and the future research on RO membrane fouling are addressed.

Indicators, Goals, and Assessment of the Water Sustainability in China: A Provincial and City-Level Study

The United Nations and scholars called for more attention and efforts for cleaner water and water sustainability. This study established a water sustainability evaluating method framework, including indicators, goals, and methods and performs provincial and city-level assessments as case studies. The framework involves six fields, surface water quality, marine environmental quality, water-soil-agriculture, water infrastructure, water conservation, aquatic ecology, water-efficient use, and pollutant emission reduction. The methods innovatively integrate multi fields and concerns of water sustainability while providing a goal-oriented evaluation and implementing the United Nations' call for the refinement and clarification of SDGs. China's overall water sustainability was evaluated as 0.821 in 2021, and have performed well in surface water quality, sea quality, water conservation, and aquatic ecology fields while performing poorly in the water-soil-agriculture field. The overall strategy, policy, and action for water sustainability could be developed based on the evaluation. The water sustainability evaluation presented the regional and field/indicator differentiations. It is necessary to implement regionally classified policies and differentiated management for sustainable water development. The correlation analysis with socioeconomic factors implies the complicated and intimate interaction between socioeconomic development and water sustainability while revealing that development stages and the inherent conditions of natural ecology and water sources bring about the differentiations. A comprehensive evaluation of water sustainability may be three-dimensional, involving water quality and ecology, development related to water, and water resources and utilization.

Investigation of land use changes in rural areas using MCDM and CA-Markov chain and their effects on water quality and soil fertility in south of Iran

The purpose of the study is to predict drought changes in Dariun, Fars Province, and their impact on water and soil quality. To prepare drought, water, and soil quality zoning maps, Landsat satellite images and the kriging method were used. The fuzzy maps and weights for each parameter were then determined using fuzzy and analytic hierarchy process (AHP) methods. Additionally, cellular automata (CA)-Markov chains were used in order to predict the impact of drought changes on water and soil quality. Using the fuzzy-AHP method, water quality and soil fertility in 2020 were lower compared to previous years, mainly because of land use changes that increased pollution. Based on results of the Markov and CA-Markov chains, approximately 31% of the region will have very poor levels of soil fertility and water quality in 2050. Further, based on remote sensing indicators, it is determined that about 25% of the region will be at high risk of drought in 2050. Thus, if adequate management of the region is not done, the possibility of living in these areas may diminish in the coming years due to drought and deteriorated water and soil quality.

Blue-green water utilization in rice-fish cultivation towards sustainable food production

Integrated rice-fish culture is a competitive alternative to rice monoculture for environmental sustainability and food productivity. Compared to rice monoculture, rearing fish in rice field ecosystems could increase food (rice and fish) production from this coculture. Moreover, the water productivity of rice-fish coculture is considerably higher than that of rice monoculture, because of double cropping. Despite these benefits, rice-fish coculture has not yet been broadly practiced. One of the potential challenges for the wider adoption of rice-fish coculture is water management. There are two forms of water involved in rice-fish cultivation: (1) blue water-surface and groundwater, and (2) green water-soil water from rainfall. The aim of this article is to focus on key factors determining the adoption of rice-fish cultivation through the effective utilization of blue-green water. We suggest that the efficient application of blue and green water in rice-fish coculture could help confronting water scarcity, reducing water footprint, and increasing water productivity.

Prospects for Simultaneously Capturing Carbon Dioxide and Harvesting Water from Air

Mitigation of anthropogenic climate change is expected to require large-scale deployment of carbon dioxide removal strategies. Prominent among these strategies is direct air capture with sequestration (DACS), which encompasses the removal and long-term storage of atmospheric CO₂  by purely engineered means. Because it does not require arable land or copious amounts of freshwater, DACS is already attractive in the context of sustainable development, but opportunities to improve its sustainability still exist. Leveraging differences in the chemistry of CO₂  and water adsorption within porous solids, here, the prospect of simultaneously removing water alongside CO₂  in direct air capture operations is investigated. In many cases, the co-adsorbed water can be desorbed separately from chemisorbed CO₂  molecules, enabling efficient harvesting of water from air. Depending upon the material employed and process conditions, the desorbed water can be of sufficiently high purity for industrial, agricultural, or potable use and can thus improve regional water security. Additionally, the recovered water can offset a portion of the costs associated with DACS. In this Perspective, molecular- and process-level insights are combined to identify routes toward realizing this nascent yet enticing concept.

Delayed use of bioenergy crops might threaten climate and food security

The potential of mitigation actions to limit global warming within 2 °C (ref. ¹) might rely on the abundant supply of biomass for large-scale bioenergy with carbon capture and storage (BECCS) that is assumed to scale up markedly in the future^2-5. However, the detrimental effects of climate change on crop yields may reduce the capacity of BECCS and threaten food security^6-8, thus creating an unrecognized positive feedback loop on global warming. We quantified the strength of this feedback by implementing the responses of crop yields to increases in growing-season temperature, atmospheric CO₂ concentration and intensity of nitrogen (N) fertilization in a compact Earth system model⁹. Exceeding a threshold of climate change would cause transformative changes in social-ecological systems by jeopardizing climate stability and threatening food security. If global mitigation alongside large-scale BECCS is delayed to 2060 when global warming exceeds about 2.5 °C, then the yields of agricultural residues for BECCS would be too low to meet the Paris goal of 2 °C by 2200. This risk of failure is amplified by the sustained demand for food, leading to an expansion of cropland or intensification of N fertilization to compensate for climate-induced yield losses. Our findings thereby reinforce the urgency of early mitigation, preferably by 2040, to avoid irreversible climate change and serious food crises unless other negative-emission technologies become available in the near future to compensate for the reduced capacity of BECCS.

Winter Potato Water Footprint Response to Climate Change in Egypt

The limited amount of freshwater is the most important challenge facing Egypt due to increasing population and climate change. The objective of this study was to investigate how climatic change affects the winter potato water footprint at the Nile Delta covering 10 governorates from 1990 to 2016. Winter potato evapotranspiration (ETC) was calculated based on daily climate variables of minimum temperature, maximum temperature, wind speed and relative humidity during the growing season (October–February). The Mann–Kendall test was applied to determine the trend of climatic variables, crop evapotranspiration and water footprint. The results showed that the highest precipitation values were registered in the northwest governorates (Alexandria followed by Kafr El-Sheikh). The potato water footprint decreased from 170 m3 ton−1 in 1990 to 120 m3 ton−1 in 2016. The blue-water footprint contributed more than 75% of the total; the remainder came from the green-water footprint. The findings from this research can help government and policy makers better understand the impact of climate change on potato crop yield and to enhance sustainable water management in Egypt’s major crop-producing regions to alleviate water scarcity.

Can Water Price Improve Water Productivity? A Water-Economic-Model-Based Study in Heihe River Basin, China

Water demand management through price and market mechanisms is crucial for agricultural water management. However, how to set an appropriate agricultural water price remains unclear due to the uncertainty regarding the response of water demand to price changes and the complexity of the hydro-economic system. Thus, this study developed a water-economic model to examine both issues in the Heihe River Basin. The empirical results revealed that the basin’s agricultural water is currently price-inelastic, with a value of −0.26, but that at 0.27 yuan/m3, elasticity is gained. At this tipping point, water demand and economic output decline by up to 10.2% and 1.6%, respectively, while water productivity increases by 7.2%. It is noteworthy that the reallocation of water and land resources from agricultural sectors to non-agricultural sectors facilitated by a water price change is the main contributor towards water productivity improvement. This signifies the importance of managing water and land resources in an integrated framework to improve water productivity in the future. Our study contributes to the literature by suggesting that future policies for water-demand management should consider pricing that encourages water saving and the reallocation of water resources to high-value uses in order to increase water productivity.

Advances and Challenges in the Water Footprint Assessment Research Field: Towards a More Integrated Understanding of the Water–Energy–Food–Land Nexus in a Changing Climate

Today, human activities are highly dependent on fossil fuels and industrialized forms of agriculture and have reached a level that could damage the Earth’s systems [...]

UK food policy: implications for nutritionists

Implications of the ‘changing world’ for nutrition and nutritionists are considered, using the UK within a global context as an illustration. The first section summarises the slow recognition by policy makers of the significance of the changing world of food and nutrition. The second section ‘Food system stress is now at a critical level’ considers the present scale of global food system stress and the failure so far sufficiently to narrow the gap between evidence and policy change. The year 2021 was earmarked when three major UN conferences had the opportunity to chart food changes ahead. The third section ‘Multi-criteria analysis helps frame 21st century nutrition science’ proposes that multi-criteria analysis is an essential methodology for nutrition within this more complex policy world; nutrition studies can no long exclude social and environmental criteria. The penultimate section ‘Nutrition science can reconnect its life science, social and environmental nutrition traditions to contribute to new paradigm formation’ suggests that nutrition science can now recombine three traditions within its own history to address this complexity: social nutrition, environmental nutrition and life sciences. The final section ‘Priorities ahead’ concludes that this multi-criteria approach to nutrition offers new routes for science and policy influence. Five priorities are identified: (1) clarification of the features of a good food system; (2) new sustainable dietary guidelines which integrate different determinants of sustainability; (3) helping consumer engagement with change; (4) developing improved policy frameworks and (5) contributing to professional channels in these processes. In the UK, while the challenge of narrowing the gap between evidence, policy and change remains daunting, the risks of not attempting to improve the transition to an ecologically sound public health nutrition are even greater.

Integrating Blue and Green Water to Identify Matching Characteristics of Agricultural Water and Land Resources in China

The uneven distribution and spatial mismatch between water and land resources (WLR) limit the utilization efficiency of agricultural water and land resources (AWLR), and then pose a threat to food production. There is a critical need to understand their matching characteristics for strategic resource allocation decisions and management. In this study, a holistic index (RSI) derived from resource equivalency analysis (REA) was developed which contributed to examine the abundance or deficiency of agricultural water and land resources (AWLR) based on the conception of generalized water resources (including blue water and green water). Results indicate that the matching degree of AWLR was the lowest in Northeast China, North China and Gansu in Northwest China, while the highest value was in Xinjiang due to the higher blue water use. In north China, other provinces suffered water scarcity except in Jilin, Liaoning, Henan, while all provinces in south China suffered land scarcity except in Tibet and Jiangsu. Meanwhile, the matching of AWLR was not exactly consistent with the distribution pattern of precipitation. The higher proportion of green water resources was not located in southeast China with rich precipitation; it had to do with water management. Too much or little water resources can result in the increasing of blue water use. The proposed approach can be a powerful instrument to implement public policies and management strategy as an attempt to improve the utilization efficiency and enhance the optimize-allocation of AWLR.

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.

Arjen Y. Hoekstra: A Water Management Researcher to Be Remembered

On 18 November 2019, the life of Arjen Y [...]

Water Ecosystem Services Footprint of agricultural production in Central Italy

The appropriate implementation of the concept of Water-related Ecosystem Services (WES) in water resources planning can support the development of productive activities and, at the same time, sustain local ecosystems. However, such implementation it is only possible when both WES supply and demand are evaluated, eventually with a spatially explicit method, for gaining insights into the ecohydrological behavior of a basin and the anthropogenic pressures on the available water resources. Based on the integration of hydrological modelling and Water Footprint (WF) analysis, this study aims at developing a methodology to analyze both the supply and demand of WES, evaluating a Water Ecosystem Services Footprint (WESF) associated with the agricultural sector. The proposed methodology is based on a 3-tiered approach: 1) evaluating the WES demand determined by the agricultural sector using the WF Assessment methodology; 2) quantifying the WES supply by applying the Soil Water Assessment Tool (SWAT); 3) estimating the green, blue, and gray WESF through dedicated indicators in order to identify the main hotspots. The methodology is applied to a specific case study in the upstream part of the Arno river basin (Central Italy). By means of subnational WF statistics the green, blue, and gray WF of the agricultural sector is calculated, determining the spatial distribution of WES demand in the catchment. SWAT results quantify the available water resources, pointing out the blue/green surface water partitioning, where precipitation is divided into 25% runoff and 46% evapotranspiration, and the associated WES supply. Merging the results, the WESF spatial pattern is evaluated, properly identifying the most critical areas in the catchment. WESF represents an operative tool to look at agricultural water management from an ecosystem-based perspective, supporting the identification of the strategies to explore the sustainable coupling of biosphere and anthroposphere.

Assessing tap water awareness: The development of an empirically-based framework

Despite the often emphasized importance of water awareness, and notwithstanding the fact that calls for increasing public awareness are becoming commonplace, most studies do not define the concept, let alone operationalise it into measurable units. This is, however, essential to measure and evaluate efforts related to water awareness such as public campaigns, customer communication and behavioural interventions. To address this gap, we conceptualise, operationalise and assess tap water awareness, hereby differentiating between cognitive awareness (head), affectional awareness (heart), and behavioural awareness (hands). In parallel, we also differentiate between tap water quality, quantity and system. By building on a variety of contemporary conceptual insights in literature and a series of expert interviews, an assessment framework is developed. A cohesive set of nine awareness components are identified and operationalised into a set of tangible questions which are put to the test in a large-scale online survey (n = 1003) in the Netherlands, applying both a traditional and modern segmentation approach based on four types of perspectives (‘quality & health concerned’, ‘aware & committed’, ‘egalitarian & solidary’, and ‘down to earth & confident’). Based on the analysis of the results of the first empirical application of our tap water awareness assessment framework, we conclude that—with a score 53.5 points out of 100—tap water awareness in the Netherlands shows ample room for improvement. Interestingly, most significant variations in awareness are generally not related to sociodemographic factors but rather apply to the four customer perspectives on drinking water that are based on people’s subjective views and preferences.

Considering the Fate of Evaporated Water Across Basin Boundaries-Implications for Water Footprinting

Water consumption along value chains of goods and services has increased globally and led to increased attention on water footprinting. Most global water consumption is accounted for by evaporation (E), which is connected via bridges of atmospheric moisture transport to other regions on Earth. However, the resultant source-receptor relationships between different drainage basins have not yet been considered in water footprinting. Based on a previously developed data set on the fate of land evaporation, we aim to close this gap by using comprehensive information on evaporation recycling in water footprinting for the first time. By considering both basin internal evaporation recycling (BIER; >5% in 2% of the world's basins) and basin external evaporation recycling (BEER; >50% in 37% of the world's basins), we were able to use three types of water inventories (basin internal, basin external, and transboundary inventories), which imply different evaluation perspectives in water footprinting. Drawing on recently developed impact assessment methods, we produced characterization models for assessing the impacts of blue and green water evaporation on blue water availability for all evaluation perspectives. The results show that the negative effects of evaporation in the originating basins are counteracted (and partly overcompensated) by the positive effects of reprecipitation in receiving basins. By aggregating them, combined net impacts can be determined. While we argue that these offset results should not be used as a standalone evaluation, the water footprint community should consider atmospheric moisture recycling in future standards and guidelines.

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.

Life Cycle Blue and Grey Water in the Supply Chain of China’s Apparel Manufacturing

Apparel manufacturing involves high water consumption and heavy water pollution in its supply chain, e.g., planting cotton, producing chemical fibers, and dyeing. This study employs a multi-regional input–output (MRIO) model to (1) assess the life cycle of blue and grey water (chemical oxygen demand (COD) specific) of China’s apparel manufacturing; (2) reveal the hidden linkage among sectors and regions in the whole supply chain; and (3) identify the key regions and upstream sectors with the most water consumption and heaviest water pollution. We found that the agricultural sector (i.e., planting fiber crops) is responsible for primary water consumption and water pollution. In addition, different provinces assume different production roles. Guangdong is a major output province in apparel manufacturing. However, its economic output is contributed to by other regions, such as blue water from Xinjiang and Jiangsu and grey water from Hebei and Shandong. Our research reveals the significance of taking an inter-regional perspective on water resource issues throughout the supply chain in apparel manufacturing. The sustainable development of China’s apparel manufacturing relies on improving water-use efficiency and reasonable industrial layout. The results are of significance and informative for policymakers to build a water-sustainable apparel industry.

An In-Depth Analysis of Physical Blue and Green Water Scarcity in Agriculture in Terms of Causes and Events and Perceived Amenability to Economic Interpretation

An analytical review of physical blue and green water scarcity in terms of agricultural use, and its amenability to economic interpretation, is presented, employing more than 600 references. The main definitions and classifications involved and information about reserves and resources are critically analyzed, blue and green water scarcity are examined along with their interchange, while their causal connection with climate in general is analyzed along with the particular instances of Europe, Africa, Asia and the WANA region. The role of teleconnections and evaporation/moisture import-export is examined as forms of action at a distance. The human intervention scarcity driver is examined extensively in terms of land use land cover change (LULCC), as well as population increase. The discussion deals with following critical problems: green and blue water availability, inadequate accessibility, blue water loss, unevenly distributed precipitation, climate uncertainty and country level over global level precedence. The conclusion singles out, among others, problems emerging from the inter-relationship of physical variables and the difficulty to translate them into economic instrumental variables, as well as the lack of imbedding uncertainty in the underlying physical theory due to the fact that country level measurements are not methodically assumed to be the basic building block of regional and global water scarcity.

Systematic review on effects of bioenergy from edible versus inedible feedstocks on food security

Achieving food security is a critical challenge of the Anthropocene that may conflict with environmental and societal goals such as increased energy access. The “fuel versus food” debate coupled with climate mitigation efforts has given rise to next-generation biofuels. Findings of this systematic review indicate just over half of the studies (56% of 224 publications) reported a negative impact of bioenergy production on food security. However, no relationship was found between bioenergy feedstocks that are edible versus inedible and food security (P value = 0.15). A strong relationship was found between bioenergy and type of food security parameter (P value < 0.001), sociodemographic index of study location (P value = 0.001), spatial scale (P value < 0.001), and temporal scale (P value = 0.017). Programs and policies focused on bioenergy and climate mitigation should monitor multiple food security parameters at various scales over the long term toward achieving diverse sustainability goals.

Variation between rice accessions in photosynthetic induction in flag leaves and underlying mechanisms

Several breeding initiatives have sought to improve flag leaf performance as its health and physiology are closely correlated to rice yield. Previous studies have described natural variation of photosynthesis for flag leaves; however, none has examined their performance under the non-steady-state conditions that prevail in crop fields. Photosynthetic induction is the transient response of photosynthesis to a change from low to high light. Rice flag leaf photosynthesis was measured in both steady- and non-steady-state conditions to characterize natural variation. Between the lowest and highest performing accession, there was a 152% difference for average CO2 assimilation during induction (Ā300), a 77% difference for average intrinsic water use efficiency during induction (iWUEavg), and a 185% difference for the speed of induction (IT50), indicating plentiful variation. No significant correlation was found between steady- and non-steady-state photosynthetic traits. Additionally, measures of neither steady-state nor non-steady-state photosynthesis of flag leaves correlated with the same measures of leaves in the vegetative growth stage, with the exception of iWUEavg. Photosynthetic induction was measured at six [CO2], to determine biochemical and diffusive limitations to photosynthesis in vivo. Photosynthetic induction in rice flag leaves was limited primarily by biochemistry.

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.

Using water footprint concepts for water security assessment of a basin under anthropogenic pressures

The evaluation of water shortages and pollution levels is crucial for watershed management and sustainable development. This paper proposes a water footprint (WF) sustainability assessment approach to analyse water security in a river basin under human pressures. The methodology involves a comprehensive assessment of the current water security at different spatial and temporal levels, and identifies suitable response formulations to achieve sustainability. Field surveys and measurements (streamflow, water quality) were carried out, and the Soil and Water Assessment Tool model was used for assessing water balance components and water quality. The study was carried out in the Canale d'Aiedda river basin (Taranto, Italy), which is part of the 'area of environmental crisis' of Taranto, which requires remediation of surface water, groundwater, soil and subsoil. Considering all the anthropogenic activities in the basin, including agriculture and the treated effluent disposed of via wastewater treatment plants (WWTPs), the average WF was 213.9 Mm³ y^-1, of which 37.2%, 9.2% and 53.6% comprised respectively for WF_green, WF_blue and WF_grey. The WF sustainability assessment revealed that pollution was the main factor affecting surface water security. In particular, point sources contributed with 90% to the total WF_grey, and lower pollutant thresholds should be fixed for effluent from WWTPs in order to increase water quality of the receiving water body. In addition, for assuring water security the extension of the natural areas should be increased to support biodiversity in the river basin and soil management strategies should be improved to allow more water to be retained in the soil and to reduce nutrients in surface runoff. This study demonstrates that the WF sustainability assessment is a feasible approach for integrated water resources management, as well as offering a much broader perspective on how water security can be achieved in a Mediterranean basin affected by multiple anthropogenic stressors.

The Water Footprint of the United States

This paper commemorates the influence of Arjen Y. Hoekstra on water footprint research of the United States. It is part of the Special Issue “In Memory of Prof. Arjen Y. Hoekstra”. Arjen Y. Hoekstra both inspired and enabled a community of scholars to work on understanding the water footprint of the United States. He did this by comprehensively establishing the terminology and methodology that serves as the foundation for water footprint research. His work on the water footprint of humanity at the global scale highlighted the key role of a few nations in the global water footprint of production, consumption, and virtual water trade. This research inspired water scholars to focus on the United States by highlighting its key role amongst world nations. Importantly, he enabled the research of many others by making water footprint estimates freely available. We review the state of the literature on water footprints of the United States, including its water footprint of production, consumption, and virtual water flows. Additionally, we highlight metrics that have been developed to assess the vulnerability, resiliency, sustainability, and equity of sub-national water footprints and domestic virtual water flows. We highlight opportunities for future research.

Water Resources for Sustainable Healthy Diets: State of the Art and Outlook

Sustainable healthy diets are high on the research and policy agendas. One of the crucial resources to provide such diets are water resources. This paper provides a brief overview of the current research state regarding this topic, with a focus on the water footprint concept, as latter quantifies water use along a supply chain. The water footprint (WF) quantifies blue and green water consumption, as both these water resources are essential for food and energy production as well as for the environment. Different kinds of information are embedded in a dietary WF and different data sources and modelling approaches exist, leading to WF dietary amounts that are not always directly comparable. A full sustainability assessment of a dietary WF encompasses three components: (1) an equity assessment of the total WF amount; (2) an efficiency assessment for each food item in the diet as well as (3) an impact assessment (blue water stress and green water scarcity) for each food item in the diet. The paper concludes with an outlook on future research on the topic, listing the following points: (1) future clarity in system boundary and modelling assumptions, with comparison of results between different approaches; (2) full sustainability assessments including all three components; (3) dietary footprint family assessments with the WF as one member; (4) WF assessments for multiple dietary regimes with support to the development of local dietary guidelines and (5) assessment of the synergies with LCA-based mid-point (scarcity-weighted WF) and end-point (especially human health) indicators and evaluation of the validity and empirical significance of these two indicators

Water Footprint Study Review for Understanding and Resolving Water Issues in China

The water footprint (WF) is a widely recognised and comprehensive indicator of both the direct and indirect appropriation of freshwater. It has been utilised for diverse functions, including as a key indicator of the planetary boundaries and United Nations Sustainable Development Goals. Focusing on the nation with the greatest WF, i.e., China, this study reviews journal articles both in English and Chinese published from January 2003 to June 2020. Using CiteSpace and bibliometric analysis of papers, journals, and keywords, we explore state-of-the-art WF accounting, driving forces, and effects. Visible differences in WF accounting keywords and spatial scales between English and Chinese literature are identified. Reported WF values for the same product varied across studies, and there was a lack of information regarding uncertainties. Key driving factors have been largely investigated for agricultural WFs but not for other sectors. The WF impact analyses primarily assess the environmental effects, ignoring the associated social and economic impacts. The development of WF studies has improved our understanding of water issues in China. However, there are still existing knowledge gaps to be filled to find solutions to WF-related issues.

Rainwater Harvesting Techniques to Face Water Scarcity in African Drylands: Hydrological Efficiency Assessment

The sub-Saharan climate is experiencing a marked increase in temperature and intensification of precipitation intensity and variability. Besides, longer dry spells are compromising the reliability of local agricultural practices. The present study provides a comprehensive investigation about the benefits induced by using indigenous rainwater harvesting techniques (RWHT) against hydrometeorological threats affecting the Sahelian areas. Different RWHT have been tested in term of runoff retention, infiltration increase into the root zone, and soil water stress mitigation. To achieve these purposes, hydrological processes at the field scale have been investigated using a two-dimensional distributed hydrological model. To make the study representative of the whole Sahelian areas, several simulations were carried out adopting a wide range of input parameters based on conventional values of those areas. The results reveal that RWHT may lead to a runoff retention up to 87% and to double the infiltration. Intercepting and storing runoff, RWHT increase the water content in the root zone and the right design can diminish the crop water stress. Furthermore, the results show that adopting RWHT makes it possible to extend the growing season up to 20 days, enhancing the yield. These benefits contribute to the reduction of the climate-related water stress and the prevention of crop failure.

Sustainable food system policies need to address environmental pressures and impacts: The example of water use and water stress

Sustainable food systems are high on the political and research agendas. One of the three pillars of sustainability is environmental sustainability. We argue that, when defining related policies, such as policies under the European Green Deal, both environmental pressures and impacts carry important and complementary information and should be used in combination. Although the environmental focus of a sustainable food system is to have a positive or neutral impact on the natural environment, addressing pressures is necessary to achieve this goal. We show this by means of the pressure water use (or water footprint) and its related impact water stress, by means of different arguments: 1) Water use and water stress are only weakly correlated; 2) water use can be evaluated towards a benchmark, addressing resource efficiency; 3) water use is used for resource allocation assessments within or between economic sectors; 4) water amounts are needed to set fair share amounts for citizens, regions, countries or on a global level 5) the pressure water use requires less data, whereas water stress assessments have more uncertainty and 6) both provide strong communication tools to citizens, including for food packaging labelling. As a result, we present a water quantity sustainability scheme, that addresses both water use and water stress, and can be used in support of food system policies, including food package labelling.

Mesophyll CO2 conductance and leakiness are not responsive to short- and long-term soil water limitations in the C4 plant Sorghum bicolor

Breeding economically important C₄ crops for enhanced whole-plant water-use efficiency (WUE_plant ) is needed for sustainable agriculture. WUE_plant is a complex trait and an efficient phenotyping method that reports on components of WUE_plant , such as intrinsic water-use efficiency (WUE_i , the rate of leaf CO₂ assimilation relative to water loss via stomatal conductance), is needed. In C₄ plants, theoretical models suggest that leaf carbon isotope composition (δ¹³ C), when the efficiency of the CO₂ -concentrating mechanism (leakiness, ϕ) remains constant, can be used to screen for WUE_i . The limited information about how ϕ responds to water limitations confines the application of δ¹³ C for WUE_i screening of C₄ crops. The current research aimed to test the response of ϕ to short- or long-term moderate water limitations, and the relationship of δ¹³ C with WUE_i and WUE_plant , by addressing potential mesophyll CO₂ conductance (g_m ) and biochemical limitations in the C₄ plant Sorghum bicolor. We demonstrate that g_m and ϕ are not responsive to short- or long-term water limitations. Additionally, δ¹³ C was not correlated with gas-exchange estimates of WUE_i under short- and long-term water limitations, but showed a significant negative relationship with WUE_plant . The observed association between the δ¹³ C and WUE_plant suggests an intrinsic link of δ¹³ C with WUE_i in this C₄ plant, and can potentially be used as a screening tool for WUE_plant in sorghum.