This Special Issue addresses topics on the water–energy–food (WEF) nexus along with other water-related topics, such as water resources, irrigation and drinking water supply systems, hydraulics and pollution. Several threats jeopardize freshwater availability and quality, energy and food availability. Integrated management approaches are absolutely necessary for pursuing sustainability. This Special Issue addresses various subjects and includes 29 peer-reviewed papers that have been grouped into the following categories: the WEF nexus, water resources and irrigation systems, drinking water supply systems, hydraulics and pollution. Some of them were selected from the Third Efficient Water Systems (EWaS) International Conference, entitled “Insights on the Water–Energy–Food Nexus,” after a thorough content update. Summaries of the papers are briefly presented in this Editorial.

Freshwater use is recognized as one of the nine planetary boundaries. However, water scarcity is a local or regional phenomenon, meaning that the global boundary must be spatially downscaled to reflect differences in water availability. In China, as in most countries, irrigation is the major freshwater user, closely linking food security to the freshwater boundary. To provide evidence supporting environmentally sustainable water use in China’s food production, this study explores how a grain production shift affects the national water-scarcity footprint (WSF) and the potential to reach sustainable water use limits while maintaining the current grain production level. We found that the historical breadbasket shift towards water-scarce northern regions has increased the WSF by 40% from 1980 to 2015. To operate within the boundary, national irrigation needs to be reduced by 18% in hotspot regions, with implications of a 21% loss of grain production. However, this loss can be reduced to around 8% by closing yield gaps in water-rich regions. It demonstrates the high potential of integrating crop redistribution and closing yield gaps to achieve grain production goals within freshwater boundaries. This Chinese case study can be representative of the challenges faced by many of the world’s countries, where pressures on land and water resources are high and a sustainable means of increasing food supply must be found.

While agriculture places the greatest demand on water resources, increasing agricultural production is worsening a global water shortage. Reducing the cultivation of water-consuming crops may be the most effective way to reduce agricultural water use. However, when also taking food demand into consideration, sustaining the balance between regional water and food securities is a growing challenge. This paper addresses this task for regions where water is unsustainable for food production (Beijing-Tianjin-Hebei Region for example) by: (i) assessing the different effects of wheat and maize on water use; (ii) analyzing virtual water and virtual land flows associated with food imports and exports between Beijing-Tianjin-Hebei and elsewhere in China; (iii) identifying sub-regions where grain is produced using scarce water resources but exported to other regions; and (iv) analyzing the potentiality for mitigating water shortage via Land-Water-Food Nexus. In the Beijing-Tianjin-Hebei Region, the study reveals that 29.76 bn m3 of virtual water (10.81 bn m3 of blue virtual water) are used by wheat and maize production and 8.77 bn m3 of virtual water used in nearly 2 million ha of cropland to overproduce 12 million ton of maize for external food consumption. As an importing-based sub-region with high population density, Beijing & Tianjin imported mostly grain (wheat and maize) from Shandong Province. Then, Hebei Province, as an exporting-based sub-region with severe water shortage, overproduced too much grain for other regions, which aggravated the water crisis. To achieve an integrated and sustainable development of the Beijing-Tianjin-Hebei Region, Hebei Province should stop undertaking the breadbasket role for Beijing & Tianjin and pay more attention to groundwater depletion. The analysis of the Land-Water-Food Nexus indicates how shifts in cultivated crops can potentially solve the overuse of water resources without adverse effects on food supply. It also provides meaningful information to support policy decisions about regional cropping strategies.

Uzbekistan, being historically one of the most populated and agriculture-based republics in the former Soviet Union, still features quite high annual population growth rates and great dependence on agriculture as a backbone for the rest of the economic reforms. With water playing an extremely important role in producing a sufficient food base for the country's growing population and earning much needed foreign exchange for the government to ensure overall economic development, the pressures on this scarce resource will obviously and inevitably grow, putting it much at risk over a long-term perspective. So would available water be enough to meet ever-increasing demands from major economic uses in the foreseeable future, and what can be the options for meeting such demands - these are the key questions raised and researched in this article. As such the research concentrates on the two major country-specific scenarios with water and its multiple uses for Uzbekistan - the business as usual and the best case. Both scenarios discuss possible future implications for the next quarter-century given certain assumptions. Finally when summarizing the findings, the paper provides conclusions and recommendations as to how the model and further scenarios can be better optimized given the trans-boundary nature of most water resources in Central Asia where Uzbekistan geographically belongs.

The tourism industry contributes significantly to the growth of the global economy and is considered to be strongly associated with a large amounts of water and energy consumption. In this study, the tourism water footprint (TWF) and the tourism energy footprint (TEF) of 138 sectors were investigated to examine the water-energy-food (W-E-F) nexus in the Chinese tourism industry from 2012 to 2017 by developing the water- and energy-based environmentally extended input-output analysis with the tourism satellite account. This study revealed that the W-E-F supply groups consumed total 15,556 million m³ of water and 4,964 million tce of energy to support the Chinese tourism industry. The largest contributor to the total TWF is the indirect water use from the food supply group (65%), while the largest proportion of total TEF is contributed by the direct energy use from 11 tourism direct sectors (63%), most especially the air transport sector. A much larger growth of the tourism industry was observed in 2017 compared to that of 2012. The structure decomposition analysis revealed that the growth of the overall water and energy consumption of China tourism is mainly driven by the growth of the total tourism expenditure, i.e. the scale effect. It is the same case for the food supply group associated with the Chinese tourism industry. In contrast, the contribution of the changes to the tourism expenditure composition is relatively low. Furthermore, the growth in water and energy consumption can be offset effectively by reducing the water and energy use coefficient and adjusting the economic production structure of tourism and its associated food supply group. In sum, the food supply and air transport sectors play a crucial role in the water-energy-food nexus of the tourism industry. Therefore, in the future, focus should be placed on improving the water and energy use efficiency of these sectors as well as enhancing their production structures.

Virtual water or land use is the volume of water or area of land, respectively, used to produce a unit food commodity that is traded. Estimates of future virtual water or land use (as potential mechanisms for mitigating against food insecurity due to resource scarcity) are limited by the need for complex modelling and data requirements regarding trade, for which the data or expertise might be rare or unavailable. This paper presents a simple food balance approach for estimating the status quo food demand and supply and associated virtual water or land use transfers under future conditions. The method is spatially-scalable, accessible to a wider range of users, and illustrated using UK feed barley supply. Key features of the method are: ● Proportionate distribution of a target food item over utilization components is estimated from the FAO Food Balance Sheet of the country of analysis and used to distribute future supply over utilization components. ● The balance between demand and supply is used to estimate the direction and magnitude of virtual water or land use transfers. ● The method can be scaled up from national to regional and global levels and to cover multiple food items.

The aim of this study was to analyze the influence of organic fertilizer on the availability of natural food (plankton and benthos) and water quality. Two fertilization protocols were adopted using inorganic and organic fertilizers with shrimp (stocked treatment) and their controls (unstocked treatment). Experimental units consisted of 12 circular fiberglass tanks (500 l) with estuarine sediment, individual aeration and no water exchange. In stocked treatments were used 40 juveniles/m², and they were fed with 35% crude protein marine shrimp ration, three times a day. Under the organic fertilization protocol, the plankton showed higher abundance of Nitzschia and rotifers, the phytobenthos consisted mainly of Nitzschia, Amphiprora and Oscillatoria, the epibenthos was represented mainly by nematodes and rotifers, and the macro-invertebrates were mainly oligochaetes. In relation to inorganic fertilization, the plankton was represented mainly by Coscinodiscus and rotifers, the phytobenthos consisted mainly of Amphiprora and Oscillatoria, the epibenthos was represented mainly by nematodes and rotifers, and the macro-invertebrates were mainly oligochaetes. Dissolved oxygen was higher for organic fertilizer (6.16 ± 0.98 mg/l) than for inorganic (5.92 ± 1.19 mg/l) while the other water quality parameters did not present significant differences. Survival was similar in the two fertilization regimes (96.6%). Final body weight was 11.89 ± 1.73 g for the inorganic fertilizers and 12.28 ± 1.71 g for organic fertilizer. It is concluded that wheat bran showed good performance in the water quality without exchange, in the availability of natural food, and in the growth and survival of the shrimps in the microcosms.

Food security is a high priority issue on the Chinese political agenda. China's food security is challenged by several anthropogenic, sociopolitical and policy factors, including: population growth; urbanization and industrialization; land use changes and water scarcity; income growth and nutritional transition; and turbulence in global energy and food markets. Sustained growth in agricultural productivity and stable relations with global food suppliers are the twin anchors of food security. Shortfalls in domestic food production can take their toll on international food markets. Turbulence in global energy markets can affect food prices and supply costs, affecting food security and poverty. Policy safeguards are needed to shield food supply against such forces. China must make unremitting policy responses to address the loss of its fertile land for true progress towards the goal of national food security, by investing in infrastructure such as irrigation, drainage, storage, transport, and agricultural research and institutional reforms such as tenure security and land market liberalization. The links between water and other development-related sectors such as population, energy, food, and environment, and the interactions among them require reckoning, as they together will determine future food security and poverty reduction in China. Climate change is creating a new level of uncertainty in water governance, requiring accelerated research to avoid water-related stresses.

This study investigates food trade patterns in relation to water resources availability in the Southern and Eastern Mediterranean countries (SEMED). Examinations show that most of these countries have a high dependence on the import of water intensive crops -- cereal, vegetable oil and sugar, in the domestic food supply. The region as a whole is marginally a net exporter of fruits and vegetables, while variations are substantial across countries. Multi-variable regression analyses show that intensification of water scarcity is an important factor in explaining the increase in food import in the SEMED countries during the past two decades. It also finds that while GDP per capita has a strong influence on the level of food import in a country, its impact on changes in the import during the same period is rather modest. No significant relationship is found between the trade of fruits and vegetables and water resources availability. The projection on food import with respect to the decline in per capita water resources availability results in an increase of 40%, 39% and 14%, respectively, for cereal, vegetable oil and sugar by 2020 in the region, holding other factors constant. The European Union (EU) is the major food trade partner of the SEMED countries, except for cereal. About 70% of the fruit export and 55% of the vegetable export of the region currently go to the EU market. Expanding the export of fruits and vegetables is conducive to improving the value of water use in the SEMED countries. However, the expansion is constrained partly by the barriers in the destination markets, notably the EU.