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Aim: Assessing water consumption in intercropping systems relative to sole crop systems is important for planting system planning. Methods: This study focused on wheat/maize (Triticum aestivum L./Zea mays L.) relay intercropping to evaluate water use advantage of relay intercropping system based on the same period. Field experiments were conducted from 2014 to 2016, and three cropping patterns were designed: sole wheat, sole maize, wheat/maize intercrops. Method for evaluating water use advantage in intercropping was revised by considering water consumption of sole crops during the fallow period (periods where no plants are grown). Results: Intercropping grain yield was higher than sole cropping yield. Based on the existing method, the intercropping system had 20.4% greater water use than the sole cropping system and the water equivalent ratio (WER) was lower than 1; after revision, intercropping had 7.7% less water use than sole cropping, and the WER was greater than 1. Before revision, intercropped wheat used 3.1% more water than sole wheat, and the intercropped maize used 38.8% more water than sole maize; after revision, intercropped wheat used 24.4% less water than sole wheat, and intercropped maize used 11.0% more water than sole maize. Conclusion: These results indicated that the revised method can be better used to evaluate water use advantage of relay intercropping system. This study implied that wheat/maize intercropping increased both yield and water use based on revised method, and relay intercropping can be a suitable production practice employed in fallow policy, especially in areas with limited water. [ABSTRACT FROM AUTHOR]

Growth in water consumption with intensified virtual water (VW) flows from increased production and consumption of both meat and feed crops threatens the sustainability of water resources in water‐scarce countries and export regions. However, a sustainability assessment of both water footprints (WFs) and VW flows related to animal products at a subnational scale is lacking. Here we estimate direct and indirect WFs as well as the inter‐provincial VW flows associated with pork production and consumption in China for the years 2008 and 2017. The contributions of feed crop production and consumption were identified. Both life cycle assessment and WF network frameworks were applied to evaluate the sustainability of blue WF and VW flows. Results show that the national annual consumptive (green‐blue) WF and degradative (gray) WF of pork production increased by 8.7% and 15.8%, respectively. More than 80% of the blue WF in pork production was unsustainable. By 2017, 62% of the unsustainable blue WF and 64% of the water scarcity footprints of pork production in the south resulted from consuming the feed crops from the north. This analysis highlights the importance and provides feasible approaches to uncover remote geographical effects on regional water scarcities from different steps in the value chains of livestock products. Key Points: Over 80% of the blue water footprint of pork production in China is unsustainableOne‐third of pork‐related scarce water is consumed in low‐water‐scarce provincesOne‐fifth of the north‐to‐south virtual water embodied in feed returns by pork [ABSTRACT FROM AUTHOR]

Agricultural sectors are facing various environmental threats, such as land degradation and water resource depletion. Agricultural water use and cropping patterns are closely linked to each other, with both related to the regional climate. This study evaluated the impacts of future climate and agricultural land‐use changes on agricultural water consumption in the Hetao Irrigation District (HID), China. The results show that owing to an increase in temperature and a decrease in precipitation, the future climate in the research area will become warmer and dryer, which will increase the water demand of crops. Future climate in the HID will lead to a 10.5% increase in total irrigation water demand under a scenario of high greenhouse gas emissions and a 6.9% increase under a scenario of low greenhouse gas emissions. Results of the grey prediction modeling indicate that the amount of water allocated to the agricultural sector will decrease, which will make it difficult to meet crop irrigation demands. The results of the gray model also show that the cropping pattern in the HID will vary over time, and the proportion of the area of cash crops will increase by 5.3% during the next decade. Regional agricultural water use can be reduced by adjusting the cropping pattern under irrigation water limitations. Meanwhile, the saved water can be used for soil desalination in cultivated land in the HID. Consequently, adjusting the cropping pattern is a nature‐based solution by which to address climate change and guarantee the sustainable use of regional water and land resources. [ABSTRACT FROM AUTHOR]

Abstract: Irrigation plays an increasing important role in agriculture of China. The assessment of water resources utilization during agricultural production process will contribute to improving agricultural water management practices for the irrigation districts. The water footprint provides a new approach to assessing the agricultural water utilization. The present paper put forward a modified calculation method to quantify the water footprint of crop. On this basis, this paper calculated the water footprint of major crop in Hetao irrigation district, China. Then, it evaluated the influencing factors that caused the variability of crop water footprint during the study period. Results showed that: 1) the annual average water footprint of integrated-crop production in Hetao irrigation district was 3.91m3 kg−1 (90.91% blue water and 9.09% green water). The crop production in the Hetao irrigation district mainly relies on blue water; 2) under the integrated influences of interannual climate variability and variation of agricultural inputs, the water footprint of integrated-crop production displayed a decreasing trend; 3) the contribution rate of the climatic factors to the variation of water footprint was only −6.90%, while the total contribution rate of the agricultural inputs factors was −84.31%. The results suggest that the water footprint of crop mainly depends on agricultural management rather than the regional climate and its variation. The results indicated that the water footprint of a crop could be controlled at a reasonable level by better management of all agricultural inputs and the improvement of water use efficiency in agriculture. [Copyright &y& Elsevier]

Water shortage is the main bottleneck restricting the sustainable development of rain-fed jujube (Ziziphus jujuba Mill.) orchards in the loess hilly region of China. Given the effect of mulching on soil moisture conservation, straw mulching (SM) and jujube branch mulching (BM) were applied to a rain-fed jujube orchard in this study. Soil moisture dynamics, soil water storage, water consumption, and soil moisture attenuation after typical rainfall under SM, BM, and clean tillage (CT) were studied. The results showed the following: (1) The 0–60 cm soil layer was the seasonal fluctuation layer of soil moisture under SM, BM, and CT in both the normal precipitation year and the dry year studied. The moisture contents of the 0–60, 60–160, and 160–280 cm soil layers under SM and BM were higher than that under CT in the three experimental years studied, and SM showed the most obvious effect of increasing soil moisture. (2) SM and BM showed a significant soil water storage effect in all of the jujube growth stages, and SM had a better water storage effect than BM. (3) SM reduced the amount of water consumption by 94.3, 60.8, and 121.3 mm compared to CT in the whole jujube growth period in 2014, 2015, and 2016, respectively. The amount of water consumption of BM decreased by 34.8 and 31.0 mm compared to that of CT in the whole growth period in 2014 and 2015, respectively. (4) CT had the maximum soil moisture loss rate under continuous drought after rainfall. The soil moisture loss rate of CT was above 37.3% on the eleventh day after typical rainfall in 2014, 2015, and 2016. With the extension of drought, the soil moisture loss rate under SM increased slowly. This study suggests that SM is the best mulching measure for rain-fed jujube orchards, and pruned jujube branches can also be used for in situ mulching to obtain a certain moisture conservation effect. [ABSTRACT FROM AUTHOR]

Jointly influenced by natural factors and artificial protection measures in recent years, the vegetation coverage of the Loess Plateau has significantly increased. However, extensive vegetation recovery can result in massive water consumption and a severe soil water deficit, which poses a great threat to the sustainable development of the regional ecological system. Maintaining the balance between precipitation and water consumption is an important foundation of ecological security in the Loess Plateau. Based on this, the present study used the GRACE (Gravity Recovery and Climate Experiment) gravity satellite data to simulate the annual actual water consumption from 2003 to 2014 and to analyze the temporal and spatial evolution of the regional precipitation and the actual evapotranspiration (AET). This study also applied the newly developed rainwater utilization potential index (IRUP) to quantify the sustainability of the water balance in the Loess Plateau. The spatial-temporal patterns of precipitation, potential evapotranspiration, and AET from 2003 to 2014 in the Loess Plateau were all analyzed in this study. Based on the results, the annual average precipitation (AAP) and AET in the entire Loess Plateau had significant increasing trends. The analysis of the spatial distribution reveals that the AET was decreasing from the southeast to the northwest in the Loess Plateau. However, the average values of potential evapotranspiration did not obviously change. Based on the estimated AET result, it was determined that the average IRUP had an increasing trend. The increase in the IRUP is due to an increased rate of precipitation that is statistically higher than that of the AET. Consequently, the Loess Plateau experienced a wetting trend during the period of 2003–2014, especially after the Grain for Green project was implemented. The results in this paper were proven by using three different depths of ERA-Interim (a global atmospheric reanalysis product created by the European Centre for Medium-Range Weather Forecasts) soil water content data from the same period and the observed runoff data from 18 different hydrological sites. Consequently, it seems that the vegetation could maintain a sustainable growth with the implementation of the Grain for Green Project. [ABSTRACT FROM AUTHOR]

The integration of water footprints and virtual water flows allows the mapping of the links between production, trade, and consumption and could potentially help to alleviate water scarcity and improve water management. We evaluated the water footprints and virtual water flows of crop production, consumption, and trade and their influencing factors in the Hetao irrigation district in China for 1960–2010. The water footprint of crop production and the export of virtual water fluctuated but tended to increase during this period and were influenced mainly by agricultural factors such as crop yield, irrigation efficiency, and area sown. The water footprint of crop consumption and the import of virtual water increased during 1960–1979 and decreased during 1980–2010 and were influenced by socio-economic factors such as total population, the retail-price index, and the proportion of the population in urban areas. Most of the water footprint of production was exported to other areas, which added to the pressure on local water systems. The import of virtual water led to a saving of water for the Hetao irrigation district, while its share of the water footprint of consumption has decreased significantly since 1977. An increase in irrigation efficiency can alleviate water scarcity, and its application should be coupled with measures that constrain the continued expansion of agriculture. Full-cost pricing of irrigation water was an effective policy tool for its management. Re-shaping regional water-production and water-trade nexuses by changing crop structures could provide alternative opportunities for addressing the problems of local water scarcity, but the trade-offs involved should first be assessed. [ABSTRACT FROM AUTHOR]

A comprehensive assessment of the regional water-saving potential (WSP) for crop production is the foundation for setting targets, formulating strategies, and implementing management measures for agriculture. Water footprint (WF) for crop production is a well-known indicator of blue and green water consumption and an effective tool for evaluating blue and green WSP in crop production. The WSP evaluations based on crop WF primarily rely on crop redistribution (CR) and the crop WF benchmark (WFB). The CR can be completed relatively quickly, but the WSP is limited. In contrast, reaching an area's maximum WSP is possible with WFB, but it requires long-term and multi-aspect inputs. However, existing evaluations of regional crop WSP are often based on a single methodology, and the results are various, which confuse the policymakers at times. This study estimated both blue and green WSP of wheat and maize based on two approaches—crop redistribution (CR) and crop water footprint benchmark (WFB)—at the county level in the Yellow River basin (YRB) in different hydrological years. The WSP was 7–11% based on CR, whereas 17–24% based on the crop WFB. The green WSPs were larger than blue WSPs. Over half of counties had larger WSP based on the WFB. These values vary with the crop, region, and hydrological year. The analysis emphasises the importance of considering both blue and green water, and quantitatively comparing different water-saving methods when evaluating regional crop WSP. [Display omitted] • Crop blue and green water-saving potentials (WSPs) were assessed via two methods. • The two approaches were crop redistribution and water footprint benchmarking. • The approach with most water-saving potential varied with crop, region, and year. • Combination of two approaches provided both water saving and crop yield increases. [ABSTRACT FROM AUTHOR]

• Supplementary irrigation promoted the recovery growth of intercropped maize after wheat harvest. • The recovery growth degree was different between border rows and inner rows of intercropped maize. • The root recovery growth was earlier than the dry matter recovery in border rows with irrigation. • SPAD, P n and sap flow in both border inner rows showed obvious recovery under irrigated conditions. • Water use advantage during the recovery growth period of intercropping was evaluated at first time. Recovery growth is common in relay intercropping systems and is a feasible practice for increasing total productivity of these systems. Previous studies have focused on the description of recovery growth, but the physiological changes and water use assessment during the recovery growth period remain unclear. A field experiment was conducted in Yangling, Shaanxi province, China during the 2014–2015 and 2015–2016 growing seasons to investigate maize physiological characteristics, root morphology, and transpiration efficiency during the recovery growth period. Three cropping systems (sole wheat, sole maize, wheat/maize intercropping) and two water treatments (supplementary irrigation and rainfed) were evaluated. Wheat was more competitive than maize during the intercropping co-growth period. During the co-growth period, the aboveground dry matter of intercropped wheat was 20.1 %–37.8 % greater than for sole wheat and water consumption was 14.9 %–15.9 % greater than for sole wheat. However, plant height and aboveground dry matter of intercropped maize during the co-growth period were less than for sole maize. Total root length of intercropped maize under supplementary irrigation initially exhibited rapid growth after wheat harvest, especially in the border rows. Subsequently, aboveground dry matter showed recovery growth, with final aboveground dry matter (2-yr average) of border rows and inner rows being 1 % and 4.5 %, respectively, greater than sole maize dry matter. Relative chlorophyll content and photosynthetic rate of intercropped maize were 4.3 %–19.2 % and 1.7 %–15.9 %, respectively, higher than observed for sole maize under irrigated conditions. Transpiration efficiency of intercropped maize during the recovery period was 10 % and 50.9 % greater than observed for sole maize under irrigated conditions in 2015 and 2016, respectively. Some recovery growth did occur under rainfed conditions, but it did not completely compensate for the growth reduction that occurred during the co-growth period. Supplementary irrigation promoted recovery growth of intercropped maize. Recovery growth improves intercropped maize grain yield and efficient use of water resources. [ABSTRACT FROM AUTHOR]

• Intercropped wheat had higher water use efficiency than sole wheat. • Wheat outcompeted maize for soil water during the co-growth period. • Transpiration was higher in wheat border rows than sole wheat, especially during the dry period. • A method for evapotranspiration partitioning in wheat/maize strips was proposed. Climate change will likely intensify water shortages, so more attention should be given to the efficient use of agricultural water in agricultural production, especially under rainfed conditions. Therefore, studying and understanding crop water consumption amounts and patterns is of great importance. However, the amount of water consumed by the component crops in strip intercropping systems has received little attention. To close this knowledge gap, a two-year field experiment of sole wheat (Triticum aestivum L.), sole maize (Zea mays L.), and wheat/maize strip intercropping was carried out under rainfed conditions. Soil water content, sap flow, soil water evaporation, and evaporation of canopy interception were measured both in intercrops and sole crops. Soil water movement between strips, evapotranspiration components, and water use efficiency were calculated. Compared with corresponding sole crops, intercropping increased water consumption of wheat and maize during the growing period of each crop. Intercropped wheat obtained soil water from the adjacent maize strip during the co-growth period, while intercropped maize obtained soil water from the adjacent wheat strip after wheat harvest. The amount of water obtained by maize was much less than the amount of water obtained by wheat. The transpiration of intercropped wheat was greater than that of sole wheat, but the transpiration of intercropped maize was lower than that of sole maize. Compared with sole cropping, intercropping increased the sap flow rate of wheat in border rows but reduced sap flow rate of maize in border rows, and this phenomenon was pronounced in the case of drought. After wheat harvest, soil water evaporation from the intercropped wheat strip was less than that from sole wheat, and evaporation from the intercropped maize strip was significantly higher than that of sole maize. The two-year average water use efficiency of intercropped wheat was 32% more than that of sole wheat, and water use efficiency of intercropped maize was 10% less than that of sole maize. These results can improve the understanding of water consumption in wheat and maize of intercropping from the point of evapotranspiration partitioning, and provide implications for water management of intercropping system under rainfed conditions. [ABSTRACT FROM AUTHOR]

Soil conservation and soil water storage are two of the main ecosystem functions affected by revegetation programs. However, the effects of revegetation on these variables have traditionally been studied separately, and there have been few efforts to assess their responses to revegetation in an integrated way. This paper evaluates the tradeoff between these responses by introducing two new indicators: the accumulation of the ratio between soil erosion protection and water consumption over a prescribed time period (EEWA) and the time specific ratio of the reduction in soil water to the reduction in erosion by vegetation (EEW). Micro-plot experiments involving different vegetation types, clipping treatments, and rainfall intensities were conducted, revealing that analyses based on EEWA identified different dominant factors and optimal management strategies than would be obtained by considering either soil conservation or soil water contents in isolation. The vegetation type, clipping, and rainfall intensity all affected soil erosion by changing the level of soil protection and the driving forces of erosion. Vegetation type and clipping affected soil water storage during and after simulated rainfall but the impact of rainfall intensity was limited because even the mildest rainfall treatment exceeded the soil's infiltration capacity. The results confirmed that it is possible to retain the soil conservation benefits of revegetation programs while avoiding detrimental soil water consumption by manipulating factors such as the vegetation type and clipping regime. These findings will provide useful guidance for increasing the sustainability of revegetation programs, particularly in arid areas where soil water is often a limiting factor for vegetation survival. • Soil conservation and soil water storage need to be simultaneously studied. • Vegetation type, clipping and rainfall intensities were influencing factors. • New indicators on soil conservation/soil water consumption trade were developed. [ABSTRACT FROM AUTHOR]

Soil water and its efficient use are critical to sustainable productivity of rainfed orchards under the context of climate change in water-limited areas. Here, we combined micro-catchments for collecting hillslope runoff, named fish-scale pits, with mulches to examine water infiltration and water consumption of fruit trees using in situ soil moisture monitoring, the micro-lysimeter and sap flow methods via a two-year experiment in a rainfed jujube orchard on China’s Loess Plateau. This experiment included four treatments: fish-scale pit with branch mulching (FB), fish-scale pit with straw mulching (FS), fish-scale pit without mulching (F), and bare land treatment (CK). The results showed that only about 50% of the rainfall infiltrated the soil for CK during the 2014 and 2015 growing seasons. The fish-scale pit without mulching experienced significantly increased rainfall infiltration by 41.38 and 27.30%, respectively, but also increased evaporation by 42.28 and 65.59%, respectively, compared to CK during the two growing seasons. The jujube transpiration significantly increased by 45.64–53.10% over CK, and the evaporation decreased by 42.47–53.50% when fish-scale pits were mulched with branches or straw. Taken together, the results show that the fish-scale pits and mulching combinations efficiently increased rainfall infiltration and jujube evapotranspiration in the experimental jujube orchard. The findings here provide an insight into the field water management for hillslope orchards in water-limited regions. [ABSTRACT FROM AUTHOR]

Cropping pattern determines the agricultural water use requirement and efficiency, as well as economic benefits of crop production. Agricultural water resources include blue water (irrigation water) and green water (soil moisture from precipitation), which have different shadow prices. The virtual water (VW) flow embedded in the interregional food trade causes burden shifts of water resources pressures in space. However, these intertwined economic and social effects have been neglected in regional cropping structure management. Using the case of the Yellow River Basin in China, here, we propose a two-stage multi-objective cropping pattern optimization scheme to maximize crop economic output, while minimize blue water scarcities (the first stage), and considered the criteria of maximum economic benefits of the interprovincial crop-related VW flows based on the shadow prices of crop green and blue water use (the second stage). Results show considerable differences in shadow prices of crop water use by colures, crops and location. With the optimized cropping pattern, which appropriately expands the planting scale of vegetables with higher water shadow price and comparative advantage and reduces the crop planting with lower water shadow price and intensive blue water consumption (e.g., soybean and wheat), blue water scarcity can be alleviated by ∼20%, combined with a ∼5% increase in crop economic output and up to ∼3% (800 million USD) higher benefits of VW flows. The premise to achieve above goals is to improve crop water resources utilization efficiency and break down the barriers of dietary preferences and trade policy. • Shadow prices of green and blue water use for crops differ in time and space. • Remote economic impacts are considered in cropping pattern optimization. • Key pathway is to transform water-intensive irrigated crops to rain-fed production. [ABSTRACT FROM AUTHOR]

Dryland revegetation can mitigate land degradation, increase vegetation coverage and terrestrial C sinks, and substantially decrease soil water storage. However, variation in soil organic C (SOC) sequestration with precipitation under large-scale ecological restoration is unclear, and the trade-off between SOC sequestration and water consumption under different vegetation types remain controversial, particularly in deep soils. This study investigated SOC storage (SOCS) and soil water storage (SWS) in 0–1000 cm profiles under various vegetation types (woodland, shrubland, grassland, and farmland) along a precipitation gradient from 406 mm to 606 mm on China's Loess Plateau. The four vegetation types exhibited similar trends in the spatial distribution of SOCS and SWS, significantly increasing as mean annual precipitation (MAP) increased, except for SWS in shrubland. In contrast, deep SOC sequestration and water deficit effects varied with vegetation type and MAP. Specifically, ΔSOCS (SOCS difference between restored vegetation and farmland) of woodland significantly decreased with increasing MAP, whereas no significant relationship occurred for shrubland and grassland; significant positive and negative linear correlations occurred between ΔSWS (SWS difference between restored vegetation and farmland) and MAP for woodland and shrubland, respectively, with no apparent relationship for grassland. Moreover, the three restored vegetation had positive correlations between ΔSOCS and ΔSWS in deep soils. Woodland had the highest SOC sequestration efficiency (ΔSOCS/ΔSWS) but also caused the most severe soil water deficit, while grassland had the lowest C and water effect. Therefore, shrublands are better for revegetation in semiarid regions, with relatively lower soil water deficit than woodland and higher SOC sequestration effect than grassland; multispecies forest plantations dominated by R. pseudoacacia may be more suitable than single-species plantations in semihumid regions. These findings highlight the SOC sequestration potential of deep soils and offer insights into dryland revegetation. • Soil water content (SWC) and soil organic carbon (SOC) of four vegetation were explored. • SOC storage (SOCS) and soil water storage (SWS) increased as MAP increased. • ΔSOCS in deep soil significantly decreased as MAP increased for woodland. • Deep SOC sequestration efficiency of Shrubland is enhanced by drier climates. [ABSTRACT FROM AUTHOR]

• Grain water-carbon footprint was accounting in mainland China. • Grain virtual water-carbon flow among regions was evaluated in mainland China. • Water saving and carbon emission reduction based on grain transfer were evaluated. • Challenges and opportunities in water-saving and carbon emission reduction were discussed. Water resource and carbon emission involved in grain production in mainland China are redistributed among provinces as the grain was transported in recent years. This study first calculated the water consumption and carbon emission during the growth of grain crops based on the water-carbon footprint theory, and then used the social-equity method to calculate the inter-regional grain virtual water and virtual carbon flow. Finally, the regional and national trends in water saving and carbon emission reduction were calculated based on the spatial and temporal differences in grain planting among provinces. In terms of virtual water-carbon, from 2000 to 2017, the amount of the inter-provincial grain virtual water flow increased from 717.4 × 108 m3 to 1472.6 × 108 m3. Heilongjiang and Guangdong are the provinces with the largest amount of grain virtual water outflow (670.9 × 108 m3) and inflow (402.8 × 108 m3) in 2017, respectively. And the total inter-provincial grain virtual carbon flow increased from 2362.7 × 104 t CO 2 e to 12,680.6 × 104 t CO 2 e. Grain transport leads to water saving and carbon emission reduction, the amount of water saving increased from 25.6 × 108 m3 to 77.0 × 108 m3 and the carbon emission reduction increased from 2.4 × 104 t CO 2 e to 847.4 × 104 t CO 2 e from 2000 to 2017. Based on research results and from the perspective of socio-hydrology combined with water saving and carbon emission reduction, the regions could optimize the integration of water saving, carbon emission reduction, and sustainable development based on coordinating the grain planting structure according to their own climatic condition, soil and water resource condition, and socioeconomic condition. [Display omitted] [ABSTRACT FROM AUTHOR]

Jointly influenced by the natural factors and the artificial protection measures, the ecological environment of Loess Plateau has been significantly improved in recent years, but which has already brought about some water-related problems. To maintain the balance between precipitation and water consumption is an important foundation for sustainable development of the ecology remediation. This study used Budyko Framework to simulate the actual water consumption of 161 sub-basins from 1990 to 2014. Based on the simulation results, the research also analyzed the evolution characteristics of water balance in Loess Plateau from 1990 to 2014. Results show that, with the increase of vegetation coverage, the regional precipitation and actual evapotranspiration were both showing a significant increasing trend, and the increasing rate of precipitation was 1.91 mm/a on average, which was greater than the increasing rate of actual evapotranspiration of 1.34 mm/a. To further demonstrate the water balance regime in Loess Plateau, the evapotranspiration coefficient (ECC) was used to quantitatively indicate the ratio of the vegetation water consumption and the total precipitation. The average values of ECC were 0.868, 0.863, 0.851 and 0.837 respectively in four sub-periods of 1990–1999, 2000–2004, 2005–2009 and 2010–2014. The above analyses indicate that with the vegetation recovery and ecological restoration, the percentage of evapotranspiration in the total precipitation is keeping decreasing and in turn the percentage of water yield in the total precipitation is keeping increasing. Consequently, it seems more sustainable for vegetation water use in most areas of Loess Plateau currently. [ABSTRACT FROM AUTHOR]

The issue of growing water scarcity has been increasingly perceived as a global systemic risk. To solve it, an integrated approach considering different perspectives of water scarcity is at a premise. In this study, we developed an approach to calculate the blue water scarcity (BWS) and integrated the production, consumption, and water transfer perspectives into a single framework. The results are as follows: The average BWS in the Hetao irrigation district was 0.491 during the 2001–2010 year period, which was much larger than the threshold of 0.30, indicating a high water stress level. From the production perspective, the agricultural sector was the largest contributor to regional water scarcity and the average BWS was as high as 0.479. From the consumption perspective, BWS related to virtual water export was much larger than that related to water consumption for making products to be consumed locally and the values were 0.422 and 0.069, respectively. Under the influence of physical and virtual water transfer, BWS changed from 0.242 (medium to high water stress level) to 0.491 (high water stress level). Strategies for reducing agricultural water consumption, such as increasing crop water productivity, improving irrigation efficiency, and promoting more reasonable irrigation water price, could be adopted in the Hetao irrigation district to alleviate regional BWS. Compared with physical and virtual water import, the virtual water export played a more important role in influencing the regional water scarcity, and the increase in crop water productivity, decrease in crop export volume, or adjustment of trade pattern from water-intensive crops to water-extensive ones could be feasible measures to decrease virtual water export for lower water stress, while the trade-offs in the product-consuming regions should be considered. [ABSTRACT FROM AUTHOR]

Over half of global livestock-related water consumption is for ruminants. Securing the increasing demand for ruminant products and their nutritional supply worldwide, especially in developing countries with limited and scarce water resources, poses new challenges. However, the evaluations of water appropriation (i.e., water footprints) and efficiencies of ruminant animals and products in time and space within large developing and populous countries remain unclear. Taking three ruminant animals (beef cattle, cows, and mutton sheep) and their meat and milk products produced within the most populous developing country, China, over the period 2008–2017 as the study case, we estimate and analyse provincial water footprints (WFs) by colours as well as their efficiencies from both perspectives of water and nutrients. The results show that the national average unit WFs decreased across species of ruminant. The northern provinces had higher unit WFs of three ruminants than the southern provinces. The WFs of beef were higher than those of the other ruminant animal products. Feed crops contributed 99% of the consumptive WFs of ruminant production in China. The water use efficiency for growing feed crops of the three ruminants increased in most provinces during the study period, which led to decreased proportion of inefficient WF of three animal products. The nutrition conversion efficiency of some animal products is found to overcome the well-known gaps between the WFs for a unit nutrient from animal products versus crops. For example, although the WF of fat per kilogram of mutton was triple of its ingested feed crops, the fat content can increase by six times when the feed crops were converted to mutton. This study reveals the necessity of evaluating the environmental impact of ruminant products from the dual perspectives of resource utilization efficiency and nutrient conversion efficiency, with a feasible evaluation method. • Water footprints of main ruminants and products are evaluated for China's provinces. • Water footprint of ruminants declined while varied in space and by species. • Feed crops contributed 99% of consumptive water footprints of ruminant production. • Dual efficiencies of resources use and nutrient conversion need to be guaranteed. [ABSTRACT FROM AUTHOR]

• Values of green water used in crop production are estimated accounting for costs. • Values of crop-related blue and green virtual water flows are compared. • Visible trade-offs between volume and value of water for crop production are observed. • Regional values of water are more sensitive than volume of water to future changes. Blue water (irrigation water) and green water (rainwater) constitute the indispensable inputs in crop production, and they virtually flow through crop trade. The valuation of water for crops is becoming essential for providing not only guidance in measuring both the biophysical and economic sustainability of agricultural water resources but also crucial information for investors and authorities engaged in water allocations. However, valuation of green water has been severely disregarded. Here, taking the Yellow River Basin as the study case, we show the feasibility of estimating the value of green water for crop production considering the costs in production processes in addition to blue water valuation. Thus, the volume versus value of blue and green water consumed in crop production as well as that of corresponding virtual water (VW) flows related to crop transfers within the basin are comparable. Fourteen major crops in current three typical years and four scenarios for the year 2050 under climate-socio-economic changes are examined. Results show that value of blue water was approximately 3 times that of green water for irrigated crops, whereas at similar level to the value of green water for rain-fed crops. Visible trade-offs between the regional volume and value of water used in crop production and that of the intra-national VW flows exist in terms of magnitude in time and space, as well as the structure by crops. The total volumes of the water footprint (WF), i.e., water consumption, in crop production and VW exports changed little over years, however the corresponding total water values was tripled and seven-folded, respectively, due to apple production expansions. Wheat was the biggest contributor in volume of VW export while apple accounted the most in value of VW export of the basin. The considered scenarios for 2050 suggested that the reduced values of crop-related WF and VW flows were more sensitive than the corresponding water quantity. This study implies the importance of managing the internal trade-offs or mutual effects between water resources and economic returns. [ABSTRACT FROM AUTHOR]

Currently, the spatial mismatch between water and animal production in China has posed a great problem for the common security of food and water. Specially, the water resources in northern China are facing severer challenges due to the poor physical water condition and the increasing virtual water outflow. To analyze the characteristics of water consumption and virtual water flow embedded in animal products, this study assessed the water footprint of major animal products in 31 provinces and simulated the virtual water flow associated with the inter-provincial animal products trade, and also evaluated the effects of virtual water flow on regional water stress and economic development. The results show that the total water footprint of animal products is 392.81 billion m3, of which meat accounts for 81.20%. Besides, the water footprint of various animal products in different regions are significantly different, mainly owing to the local climatic condition and economic development degree. The virtual water flow associated with animal products is mainly from the water-scarce and underdeveloped northern regions to the water-rich and developed southern regions, which is as much as 61.39 billion m3 in 2015, accounting for more than 15% of the total water footprint of animal products. Therefore, the current virtual water flow pattern not only seriously aggravates the water scarcity in the output areas, but also widens the economic gap between the output areas and the input areas. To effectively solve aforementioned problems, this study proposed some countermeasures, including the improvement of water use efficiency for animal production, the adjustment of regional industrial structure to low-water and high-profit degree, and the integrated management framework of physical and virtual water. [Display omitted] • There is a mismatch between water resources and animal production in China. • The water consumption characteristics related to animal products are evaluated. • The virtual water flow pattern embedded in animal products trade is simulated. • Virtual water flows mainly from the water-scarce north to the water-rich south. • Current flow pattern will threaten water security and widen the economic gap. [ABSTRACT FROM AUTHOR]

Water consumption in grain production consists of blue (i.e., surface water and groundwater) and green water (i.e., rainwater), however, is rarely distinguished in existing emergy analysis. Taking four major grain crop production systems (rice, wheat, maize, and soybean) by provinces in mainland China over the period 2001–2016 as the study case, in this study the blue and green water were differentiated, for the first time, in the emergy analysis for crop production systems based on water footprint assessment. Three indicators were estimated per crop per province per year: water resource emergy input (WEI), water resource emergy contribution ratio (WECR), and water resource emergy use efficiency (WEUE). Results show that during the study period, the total WEI into the major grain crop production systems increased by 16.61%; blue and green WEI accounted for 52.64% and 47.36%, respectively, by 2016. Although the blue WECR was higher than green WECR, it decreased significantly over the study period. The annual average green WEUE was 10.99 sej sej−1, 7.7 times the blue; moreover, it increased by 27.28% over the study period. The annual average total WECRs in nine provinces were higher than the national average, but the corresponding total WEUEs were lower than the national average; of these, four were distributed in arid and rainwater-deficient areas of northwest China. The emergy analysis of blue and green water separately provides information for a more precise and efficient water allocation as well as better cropping structures given corresponding water endowments. [Display omitted] • Blue and green water were distinguished in water emergy analysis for crop production. • Three emergy based indicators were estimated to measure the water use efficiencies. • Visible spatial and temporal heterogeneities were shown in crop-related water emergy. • Blue water and green water have different emergy in crop production systems. [ABSTRACT FROM AUTHOR]

The mismatching of grain production and consumption in space causes grain virtual water flow. Previous studies focused on the important role of virtual water trade in regional food security and its impact on water resource consumption, while this study focuses on the impact of virtual water flow on the environment. In this paper, two indexes of gray water footprint and carbon footprint were selected by footprint evaluation method to study the influence of virtual water flow on regional environment. The results show that the scale of grain virtual water flow gradually expanded, and the amount of virtual water flow increased from 67.14 Gm³ to 129.87 Gm³ from 1997 to 2014. The gray water footprint at a national scale showed a fluctuating trend, with obvious differences in temporal and spatial distribution. In addition, the total carbon footprint at the national scale increased from 290.2 Mton in 1997–430.4 Mton in 2014, basically showing a continuous increase trend. Provinces with larger gray water footprints are basically converted into import areas, and the total national gray water footprint reduced 64.74 Gm3. Meanwhile, the carbon footprint of the grain export region and import region changed significantly. Among the export areas, such as the Northeast region and the Huang-Huai-Hai region, the carbon footprint had an obvious downward trend. On the other hand, the carbon footprint of the import region in the south due to increasing of grain production to meet their own needs showed an increasing trend. Although virtual water flow reduced the gray water footprint and carbon footprint nationally, it increased the local environmental pressure on the export area. This study would be helpful in forming better water management policy and alleviating regional environment pressure. • Virtual water flow shows an environmentally friendly model in the overall situation. • Virtual water flow increases the gray water and carbon footprint in the export area. • The environmental impact rate of the export area is higher than that of import area. [ABSTRACT FROM AUTHOR]

The water footprint (WF) of crop production indicates the water consumption for crop growth in a specific area over a certain time, enabling comprehensive water use efficiency assessments to be achieved for different types of water in an irrigation district. Daily and monthly blue (irrigation water) and green (rainfall) water resources are unevenly distributed in monsoon climate areas. However, the intra-annual evolution of the WF of crop production for a monsoon irrigation district is lacking. In the current study, maize and wheat production in the Baojixia Irrigation District (BID) of Shaanxi in China selected as the case study for the period 2008–2017, where the WF of crop production was analyzed based on a regional distributed hydrological model and the associated meteorological driving factors on daily, monthly, and yearly scales were identified. Results reveal that the method of WF of crop production established in the study can be applied to hydrological simulation of irrigated areas without drainage system. The blue WFs of maize and wheat production accounted for 34% and 36% of the irrigation water supplies, respectively. On a yearly scale, precipitation had the greatest impact on the green and blue WFs of maize, while sunshine hours and temperature had the greatest impact on those of wheat, respectively. On daily and monthly scales, different meteorological factors played key roles in the WF of crop production in different typical years. The time scale effect existed in the impact of meteorological driving factors on the WF of crop production, reaching its maximum on a monthly scale. Both water shortages and water waste coexist in BID. The irrigated area should rationally allocate blue water and effectively utilize green water resource to improve crop yield. Meanwhile, the time scale effect in the WF assessment of crop production and driving factors cannot be neglected. The irrigation strategy should be adjusted to cope with the impact of meteorological conditions according to the results and actual situation. [Display omitted] • Daily and monthly water footprint of irrigated crops were analyzed. • Precipitation had the largest effect on the water footprint of maize. • Sunshine hours and temperature effected largest on the water footprint of wheat. • Monthly time scale effect of meteorological factors on water footprint was larger. [ABSTRACT FROM AUTHOR]

Here we identified and evaluated the strengths and spatio-temporal heterogeneities in 12 main socio-economic driving factors of water footprints and inter-provincial virtual water flows related to three staple crops (rice, wheat, and maize) within mainland China for 2000–2017, in consideration of the infrastructure related to irrigation, agricultural electricity and road for the first time. The irrigation, agricultural electricity, and road infrastructures in China expanded by 33.8, 4.5, and 2.4 folds, respectively, throughout the course of this study. The results show that irrigation infrastructure in water-scarce regions was the most critical driver for the effective reduction of the water footprint per unit mass of crops, particularly the blue water footprints (i.e. increasing water efficiency). As the irrigation infrastructure per unit area doubled for 2000–2008, blue water use efficiency and total blue water consumption decreased by 58% and 71%, respectively. However, the development of irrigation infrastructure has led to a larger total water footprint in crop production. Agricultural electricity and road infrastructures had increasing effects on provincial virtual water export, with varied corresponding driving strengths across spaces. The visible effects of agricultural infrastructure on regional water productivity, water consumption, and virtual water patterns should not be neglected. This analysis suggests that investments in agricultural infrastructure should consider the spatio-temporal heterogeneity of these infrastructures on local water productivity and water consumption in addition to the economic benefits. [Display omitted] • Agricultural infrastructure is core driver for water in crop production and trade. • Irrigation infrastructure lowers water per crop but enlarges regional water consumed. • Spatiotemporal heterogeneities are in driving forces for crop water consumption. [ABSTRACT FROM AUTHOR]

Water scarcity is a significant risk for meeting increasing food demand around the world. The importance of identifying the driving forces behind water consumption in agriculture and relative virtual water (VW) flows has been widely reported in order to provide practical advice for regional sustainable agricultural water resource management. However, the differences of regional driving forces behind both water consumption and VW flows were largely ignored. To fill the crucial gap, taking nine major crops grown in the Beijing-Tianjin-Hebei (BTH) region in China over 2000–2013 as the study case, we investigated the regional differences in socio-economic driving forces on both the estimated water footprint (WF) in crop production and relative inter-city VW flows for each crop per year. Results show that although there is little change in total WFs in crop production (∼43.3 billion m3/y on annual average), the WF per unit mass of crop decreased and the crop structure in the total WFs changed greatly. The BTH region was a VW importer with net VW import of 11.7 billion m3/y by 2013 but the roles of each cities were different. Inter-city VW was predominantly exported from the southern regions. The per capita GDP was the main positive driver of both total WFs and relative VW flows. Whereas economic productivity and consumption capacity were inhibiting factors for the WFs and VW flows, respectively. The levels of total crop WFs in agricultural cities were more sensitive to the effects of the main driving factors. The intensity of driving factors behind the inter-regional crop-related VW flows was shown to be directly related to regional role as an importer or exporter. Aiming for a balance between water sustainability, food security and economic developments, the current analysis suggests characteristic-based agriculture in terms of regional differences in water consumption and local roles in relative inter-regional VW flows. Especially for agricultural cities which are VW exporters, reducing water consumption per unit agricultural product and increasing economic production value per drop of water used in all sectors are equally important. Image 1 • Drivers' levels of crop water footprints and virtual water flows differ spatially. • Driving forces of virtual water flows differ between importer and exporter. • Economic growth enhances both crop-related water footprints and virtual water flows. [ABSTRACT FROM AUTHOR]

• Quantification of water footprint for three crops during 2002–2018 were reviewed. • Approaches to water footprint quantification were divided into five types. • Results are affected by spatial scale and the type of approach. The water footprint (WF) of crop production has been widely accepted as a comprehensive indicator of agricultural water consumption. Rationality and accuracy in crop WF accounting are thus prerequisites for implementation of WF assessments that yield sustainable regional agricultural water management. However, few studies have focused on the rationality of multiple quantitative approaches and the associated differences in crop WF accounting among different studies. Here we, focusing on maize, wheat and rice, review quantitatively the effects of different quantification approaches and scales on the results of crop WF accounting and simulations in relevant published research during 2002–2018 worldwide. Results show that (i) The number of studies on crop WF accounting has increased by 17 times since 2002 (~the year of creation of WF concepts); the research direction is focused on improvement of quantification and resolution in both time and space. (ii) The current approaches to WF calculation can be divided into five main types: the field crop water requirement (FCWR) approach, field soil water balance (FSWB) approach, regional water balance (RWB) approach, remote sensing (RS) approach and field measured water balance (FMWB) approach. The FCWR and FSWB approaches are more widely adopted than the other three. (iii) There were non-negligible differences in the WF accounting results among approaches and scales. At the global level, the deviations in WF for maize, wheat, and rice were relatively low among different studies, with the world average values of 0.73 m3 kg−1 ± 14.9%, 1.136 m3 kg−1 ± 13.5%, and 1.269 m3 kg−1 ± 27%, respectively. The ranges of uncertainty varied significantly when downscaling to specific countries and provinces. The maximum coefficients of variation (CV) of WF for maize, wheat, and rice in different regions were up to 40%, 49%, and 50%, respectively. (iv) The WF simulations showed very reasonable agreement and lower deviation between the FCWR and FSWB approaches. [ABSTRACT FROM AUTHOR]

• Blue and green water resources, footprints and scarcities were quantified. • Effects of irrigation on blue and green water resources were considered. • Middle reaches faced both blue and green water scarcities at least 3 months a year. Blue water (surface and ground water) and green water (water stored in unsaturated soil layer and canopy evapotranspiration from rainfall) are the two sources of water generated from precipitation and communicating vessels that define the limits of water resources (WRs) for both human activities and ecosystems. However, the blue and green evapotranspiration in irrigated fields and their contribution to blue and green water flows have not been identified in studies conducted on blue and green WRs. In addition, information on intra-annual variations in green water footprints (WFs) and water scarcities is limited. In particular, there is a lack of information on water consumption obtained from hydrological model-based blue and green water assessments at the basin scales. This study quantified, taking the Yellow River Basin (YRB) over 2010–2018 as the study case, the inter- and intra-annual variations in blue and green WRs, WFs and water scarcities at sub-basin levels. WRs and WFs were simulated using the Soil and Water Assessment Tool (SWAT) model. The results revealed that the annual average blue and green WRs of the YRB were 119.33 × 109 m3 yr−1 and 296.94 × 109 m3 yr−1, respectively, over the study period. The blue and green WFs of the crops in the middle reach were significantly larger than those of the crops in the upper and lower reaches. There were visible spatial heterogeneities in water scarcities across the basin. Several areas in the middle reaches were subject to both blue and green water scarcities (at least modest level) for a minimum of three months a year. Furthermore, the norther region of the YRB was subject to significant and severe blue water scarcity for the whole year. [ABSTRACT FROM AUTHOR]

• China's inter-provincial crop-related inefficient inter-provincial VWFs reduced. • Inter-provincial unsustainable blue VWFs increased by 8% over 2004–2013. • Trade-offs between efficiency and sustainability of VWFs existed in five provinces. The phenomenon of virtual water flows (VWFs) reveals the remote pressure on local water resources on one hand, and provides the possibility of global water saving if VWFs from water-rich places of higher water use efficiencies to water-poor or lower water use efficiencies regions on the other hand. A VWF is marked as efficient when at least half of the water footprint (WF) in producing the traded products is below the corresponding WF benchmark. Whereas the VWF is marked as sustainable when flowing from the places where the water consumption did not exceed local sustainable renewable water availability. However, most attention has been taken to the sustainability of VWFs, ignoring their efficiency and spatial-temporal variations. Here we, taking inter-provincial crop-related VWFs of twenty major crops in the mainland China over 2004–2013 as a study case, analysing the efficiency of VWFs and the sustainability of blue VWFs, as well as their mutual relationship. Results show that over the study period, although inter-provincial crop-related VWFs increased slightly by 2%, the North to South VWFs and blue VWFs increased by 41% and 2.5 times, respectively. The weight of inefficient inter-provincial VWFs reduced to 75% in 2013 from 94% in 2004, whereas the unsustainable blue VWFs increased by 8%. Trade-offs between the efficiency and sustainability of VWFs existed in five provinces. Wheat, rice, maize, and cotton were the main contributors to inefficient and unsustainable VWFs. Assessments in VWFs should account for local water resources conditions, considering both efficiency and sustainability to determine hotspots and critical products and allow appropriate management of crop production and water allocation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Age- and climate- related water use patterns of apple trees were explored. • Orchards in semihumid area had higher SWC than those in semiarid area. • Main water sources in shallow layers became shallower with stand age in two areas. • Uptake from deep layers peaked in blossom and young fruit stage in semiarid area. • Older trees absorbed more deep soil water than younger trees in semiarid area. The Loess Plateau of China is a major apple-cultivating region, but much of the Plateau is water-limited, and the expansion of apple-growing is putting pressure on soil water resources. Plants' water consumption patterns have been intensively studied to facilitate formulation of robust agricultural strategies, but previous studies have generally applied indirect methods to characterize their water use. Moreover, the few studies that have applied direct (isotopic) methods have mostly focused on shallow (0–200 cm) soil layers, usually in stands of a single age or single climatic region. To avoid these limitations, we have investigated the primary water sources of apple trees of three ages (10, 15 and 22 years) in semiarid and semihumid climatic regions of the Plateau using both natural stable isotopic signatures (δ 2H values) and injections of 2H 2 O into deep soil layers. We found that water content in apple orchards' soil decreased with increases in depth and stand age, and was higher in the semihumid area than in the semiarid area. Nevertheless, patterns of apple trees' water uptake from shallow (0–300 cm) soil layers were similar in the two climatic regions and the main water sources became shallower with increases in stand age. However, water uptake from deep (400–500 cm) soil layers was also detected, particularly in the blossom and young fruit stage in apple orchards of the semiarid area. Moreover, older trees absorbed more water from these layers than younger trees in the semiarid area (but not in the semihumid area) throughout the growing season. Excessive consumption of deep soil water inevitably results in deep soil drying and severely threatens the sustainability of apple cultivation. Our work suggests that it is necessary to take actions (e.g. supplementary irrigation, landscaping and mulching combinations) to reduce the proportion of deep soil water used by apple trees to prevent the development of dried soil layers. It also highlights the need to assess uptake patterns of plants at multiple developmental stages and ages to identify times when and places where interventions may be required or most effective. [ABSTRACT FROM AUTHOR]