Definition

A generally agreed-upon definition of a nexus approach has not yet emerged (Avellan et al. 2017). Conceptually, a nexus describes the linking of multiple resource-use practices and serves to understand interrelations among such practices. In the view of Hoff (2011), the water-energy-food nexus focuses on achieving water, energy, and food security in an emerging green economy. Within that context, the WEF nexus aims to support the respective transition through achieving greater policy coherence and higher resource use efficiency. Through reducing tradeoffs and building synergies, the intentions of the WEF nexus are to increase the security of water, energy, and food, which would result in secure access for all the people (Hoff 2011).

Introduction

In September 2015, the United Nations adopted the Sustainable Development Goals (SDGs), the Agenda 2030 which range from ending poverty in the world to gender issues. The 17 goals set as measurable variables comprise 169 concrete targets, built on the previous eight Millennium Development Goals, and are intended to guide the development of the world over the next 15 years. The objectives are universally applicable and implementable at national level taking into account the different circumstances, capacities and development stages of individual countries.

The nexus approach, which was discussed for the first time on a broad international level between experts and decision-makers at the “Bonn2011 Conference: The Water Energy and Food Security Nexus - Solutions for the Green Economy” (Hoff 2011), presents a number of interesting potential solutions. The basic concepts are founded on the principle of sustainability, which the participating states declared as a global maxim 20 years ago at the first UN Conference on Sustainable Development in Rio. The Water-Energy-Food (WEF) nexus constitutes a framework for analyzing the dynamic interrelations between water, energy, and food systems to achieve equitable water, energy, and food security and developing strategies for sustainable development (Hoff 2011). The WEF nexus postulates that water security, energy security, and food security are inextricably linked causing impacts in one or both of the others. Networked and coherent governance approaches are needed across the three sectors to understand, assess, and manage supply risks.

Particular emphasis is placed on the interconnections between the individual sustainable development goals as a basis for sustainable development and its integrative character. Nexus refers here to the interaction of the system components of individual goals in the form of mutual influence, dependency, and impact. Consciousness and the knowledge of mutual influence are not new as also for instance the integrated natural resources management (INRM) has traditionally an interdisciplinary holistic approach (Avellan et al. 2017). This is necessary for a nexus approach (Howarth and Monasterolo 2016). Nevertheless, the establishment of the nexus idea at the international strategic level represents a decisive step. Isolated, linear approaches are not suitable to solve the complex problems facing the world under resource-limited conditions. Central challenges such as water, energy, and food security are therefore treated under the term “water-energy-food nexus.” Between these three singular terms, numerous dependencies can be identified, as exemplified in Fig. 1.

Water-Energy-Food Nexus and Sustainability, Fig. 1
figure 229figure 229

Illustration of the water-energy-food nexus

Full size image

For the Global Risks 2012 report of the World Economic Forum, 469 experts assessed various risks according to their probability and potential impact (Beisheim 2013). According to the World Economic Forum (2012), water supply and food crises rank right after the financial crisis as a risk, along with high volatility in energy and food prices. In the most recent emission, the Global Risks 2018 report of the World Economic Forum underlined that environmental risks have grown in prominence in recent years. According to the World Economic Forum (2018), biodiversity is being lost at mass extinction rates, agricultural systems are under strain, and pollution of the air and sea has become an increasingly pressing threat to human health. Still, more than a billion people have no access to clean drinking water and safe sanitation, suffer from malnutrition, and cannot use modern energy sources. At the same time, climate change, a growing world population, changing consumer habits and, under- and misinvestments in infrastructure in many places are leading to an increasing shortage of resources such as water, energy sources, and land.

The interdependencies in the use of resources to secure the provision of water and energy and the production of food are becoming increasingly apparent. For example, the cultivation of agrofuels can supplant the cultivation of food and contribute to the depletion of water resources. Intensive agricultural use upstream of the watershed can increase downstream erosion and affect hydropower production. Energy subsidies for farmers make irrigation pumps affordable, but with their use, the groundwater level can be lowered. Not only climate change but also climate change measures can increase the pressure on water and land resources (World Economic Forum 2011). The nexus approach explicitly addresses these dependencies.

In this entry we wish to further illustrate (1) the concepts of water, food, and energy securities, (2) the connection of the concept of securities with sustainable development and (3) show examples of nexus methodologies that support achieving water, energy, and food security.

The Concepts of Water, Energy, and Food Security

Water Security and Integrated Water Resources Management

UN-Water proposes the following definition of water security: “The capacity of a population to safeguard sustainable access to adequate quantities of and acceptable quality water for sustaining livelihoods, human well-being, and socio-economic development, for ensuring protection against water-borne pollution and water-related disasters, and for preserving ecosystems in a climate of peace and political stability” (United Nations University UNU-INWEH 2013).

According to the World Economic Forum (2011), water security is understood as “the grossamer that links together the web of food, energy, climate, economic growth and human security challenger that the world economy faces over the next two decade.” Water security has emerged as a new discourse in water governance challenging the more traditional dominant discourse of integrated water resources management (IWRM) in the past decade (Gerlak and Mukhtarov 2015). The definition of IWRM that is most widely accepted and of relevance today was given by the Technical Committee (TEC, former Technical Advisory Committee, TAC), of the Global Water Partnership (GWP).

It states that IWRM is:

A process which promotes the co-ordinated development and management of water, land and related resources, in order to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems. (GWP 2000).

IWRM explicitly challenges conventional, partial water development and management systems and underlines the importance of an integrated approach with greater coordinated decision-making across sectors and scales. It recognizes that a pure top-down, supply-side, technology-based, and sector-based approach to water management puts mankind at a non-sustainable high economic, social, and environmental cost. IWRM and its relation to sub-sectors are illustrated in Fig. 2.

Water-Energy-Food Nexus and Sustainability, Fig. 2
figure 2210figure 2210

IWRM and its relation to sub-sectors (GWP 2000)

Full size image

IWRM has a strong sustainability dimension, expressed through:

  • Social responsibility: ensuring equal access for all users (in particular marginalized and poorer user groups) to an adequate quantity and quality of water necessary for the maintenance of individual well-being

  • Economic efficiency: delivering the most value to existing financial and water resources for the largest possible number of users

  • Ecological sustainability: requires the recognition of aquatic ecosystems as social and economic actors and the adequate distribution of their natural functions

The pressure on water resources is growing with the increasing world’s population and the resulting need for food security as well as the increasing urbanization causing an increasing energy demand. Since the 1950s, the water demand from the agriculture sector and the industry has more than tripled, while the demand from households has doubled; see Fig. 3 (Gleick 1998, 2000).

Water-Energy-Food Nexus and Sustainability, Fig. 3
figure 2211figure 2211

Evolution of the global water use – withdrawal and consumption by sector. (Source: Igor A. Shiklomanov, State Hydrological Institute (SHI St. Petersburg) and United Nations Educational Scientific and Cultural Organization (UNESCO, Paris), 1999)

Full size image

Since the 1970s, there is also an increasing water demand from the energy sector through the construction of reservoirs for water power generation and water storage.

Energy Security and Use of Renewable Energies

The International Energy Agency (IEA) defines energy security as the uninterrupted availability of energy sources at an affordable price. Long-term energy security which mainly deals with timely investments to supply energy in line with economic developments and environmental needs. Short-term energy security focuses on the ability of the energy system to react promptly to sudden changes in the supply-demand balance (source: IEA).

According to the IEA’s 2017 Medium-Term Renewable Energy Market Report (International Energy Agency (IEA) 2017), there has been substantial growth in renewables in some sectors and regions. Paolo Frankl, Head of Renewable Energy Division of the IEA, stated that renewables (including hydropower) have made “tremendous progress.” They now account for 22% of global power generation. IEA (2016) forecasts that by 2020, hydropower (4669 TWh) will provide the lion’s share of the total renewable energy production, which is projected to be 7313 TWh, or 26% of global power production (International Energy Agency (IEA) 2017). Bioenergy production (615 TWh by 2020) also needs water. In 2016, global renewable electricity generation grew 5% by 240 TWh to reach 5070 TWh (International Energy Agency (IEA) 2016). The global renewable electricity production by region, historical and projected, can be seen from Fig. 4. The figure indicates an increasing trend for the global energy demand.

Water-Energy-Food Nexus and Sustainability, Fig. 4
figure 2212figure 2212

Global renewable electricity production by region, historical and projected. (Source: http://energypost.eu/global-renewable-energy-cross-roads/). Note: the figures are from the IEA. Hydropower includes pumped storage

Full size image

Food Security

Concepts of food security have a long history and arrived in the last 30 years in the official policy thinking (Clay 2002; Heidhues et al. 2004). The term has its origin in the mid-1970s, when the World Food Conference (1974) defined food security in terms of food supply as assuring the availability and price stability of basic foodstuffs at the international and national level. Later definitions addressed demand and access issues. In 1983, the definition of the FAO focused on food access, leading to a definition based on the balance between the demand and supply side of food security. The understanding of food security moved from a more economic view to a more social ones, that includes the negative effect on the physical, social, emotional, and cognitive development of human (Pérez-Escamilla 2017). The 1996 World Summit on Food Security declared that “food should not be used as an instrument for political and economic pressure” (FAO 1996).

The current definition was developed at the FAO World Food Summit (WFS), which took place from 13 to 17 November 1996 in Rome and aimed at renewing the global commitment to fight world hunger: “Food security exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life” (FAO 1996). The background to this World Summit was, in particular, the malnutrition prevalent among large parts of the world population and the limited capacity of agriculture to meet the food needs of the future. World grain stocks were at their lowest levels since the early 1970s, prices had risen enormously, and food aid had almost halved in the years 1993–1996.

Notable progress has been made in some countries and malnutrition is slowly declining in many developing countries. Theoretically, world food production is enough to feed all people, but the poorest of the poor often have no access to it, and 815 million people suffer from hunger (FAO 2017), see Fig. 5. At the end of the summit, a declaration on global food security and an action plan on world nutrition were adopted. The FAO estimates that over the next 30 years, food production will need to increase by over 75% to ensure adequate food supplies to the world’s population of approximately 7.6 billion people in 2017.

Water-Energy-Food Nexus and Sustainability, Fig. 5
figure 2213figure 2213

Prevalence and number of undernourished people in the world, 2000–2016. Figures for 2016 are projected estimates (United Nations Food and Agricultural Organization (FAO) 2017)

Full size image

The links within the WEF nexus in terms of global food security are obvious as food production is by far the largest consumer of global freshwater supplies, representing an average of 70% of the freshwater consumption on the global scale. Further, there are also quite high energy needs in food production as for irrigation, machinery, transport, and storage of food. As reflected in SDG 2, one of the main global challenges is ensuring food security for a growing global population (UN-DESA 2011), which is projected to rise to around ten billion by 2050 (FAO 2017). The resulting need of increasing the food production by 75% globally by 2050 requires a holistic approach to all forms of malnutrition, productivity and incomes of small-scale food producers, resilience of food production systems, and the sustainable use of biodiversity and genetic resources (FAO 2017). It requires a sustainable and innovative use of water resources which are needed to grow that food, including the use of wastewater in agriculture.

The Nexus Approach to Foster Sustainable Development

The WEF nexus provides the framework for the sustainable linkage of the water, energy, and food sectors (Kurian 2017; UNU-FLORES 2015; Walker et al. 2014). Water is a key factor for food production along the entire value chain. Energy is also of vital importance for food production, water supply, and sanitation. Thirty percent of global energy consumption is needed for food production. There are a large number of synergies and conflicting goals between the three sectors (Leck et al. 2015). For example, extracting water for the agricultural sector can increase food production but leads to a reduction in runoff and hydroelectric potential.

The future supply of water, food, and energy largely depend on global developments that will change the supply and demand for these resources. Among the most important drivers are population development, climate change, and changes in living standards (von Braun and Mirzabaev 2016). All components of the global population development (birth rate, life expectancy, and migration) are characterized by economic and social conditions as well as by individual behavior.

The development of living standards and consumption patterns toward higher resource consumption per capita is driven by two forces: economic development (prosperity) and international market integration (globalization), which also increases the availability of goods. Demographic aspects, such as changes in age structures, influence this factor. At the same time, climate policy has consequences for the nexus of water, energy, and food security (WEF nexus). All three trends can cause supply risks to increase. Both the growing demand for water, energy, and food by more people or ever higher demands and the decreasing supply of these resources as a result of climatic changes are global processes, which, however, are predominantly local and regional (Obersteiner et al. 2016). Therefore, politics is required at all levels. Although complex relationships and risks in the supply of water, energy, and food can easily be seen, a corresponding “nexus” on the part of the policy is missing. In order to deal adequately with the problems, cross-sectoral and cross-border cooperation and coherence must be strengthened (Stiftung Wissenschaft und Politik).

Yillia (2016) described the water-energy-food nexus in the context of the SDGs, which considers in more detail the framework of the nexus approach. Specifically, the following SDG goals are considered:

  • SDG 2. Stop hunger, achieve food security and nutrition, and promote sustainable agriculture.

  • SDG 6. Ensure availability and sustainable management of water and sanitation for all.

  • SDG 7. Ensure access to affordable, reliable, sustainable, and modern energy for all.

The interface with other SDGs presents concrete content-related contributions and solution approaches derived, for instance, from wastewater treatment or responsible consumption in the nexus (UN-Water 2013, 2016).

The nexus perspective investigates the interdependencies across the water, energy, and food sectors and influences policies in related areas, climate and biodiversity. Taking these relationships into account can result in greater resource efficiency while minimizing environmental hazards and impacts.

Allouche et al. 2014 discussed the assumption that discourses over nontraditional forms of securities are affecting ways of policy framing of long-term sustainability in the area of water, energy, and food, which was originally based on an equilibrium thinking between these aspects as summarized by the idea of balancing. Allouche et al. (2014) agreed the approach of Leach et al. (2010) that recent understanding of ecological systems has shifted from seeing nature as “in balance” to recognizing ecological systems as being in a dynamic non-equilibrium with potentially nonlinear responses and multiple stable states. Leach et al. (2010) prioritized different aspects of systems dynamics (see Fig. 6) as dynamic properties of sustainability and proposed different strategies to deal with them.

  • Stability: if a system is assumed to move along an unchanging path, the strategy may be designed to exercise control.

  • Resilience: if limits to control are acknowledged, the strategy might be to resist shocks in a more responsive way.

  • Durability: if a system may be subject to stresses and shifts over time, interventions may attempt to control the potential changes.

  • Robustness: strategies that embrace both the limits to control and openness to enduring shifts.

Water-Energy-Food Nexus and Sustainability, Fig. 6
figure 2214figure 2214

Dynamic properties of sustainability (Leach et al. 2010)

Full size image

Thus, these criteria are also relevant for the implementation of the WEF nexus to foster sustainable development. The nexus approach, from an economical point of view, aims to integrate sectors through making them visible and thereby to address externalities that link sectors together (Allouche et al. 2014) with the scope to openly discussing trade-offs between them.

Practical Application of the Nexus Approach

By now, there are pilot applications of the WEF nexus, among others driven by UN organizations. The developments in the WEF nexus involve cross-border and networked or even systemic risks. These are “highly interconnected problem contexts with unpredictable effects in terms of scope, depth and time horizon, the management of which due to the complexity of the effects, uncertainty and ambiguity is associated with considerable knowledge and assessment problems” (Renn et al. 2007). Foresighted governance of risks opens up opportunities for positive (side) effects if it strengthens coping capacities. The WEF nexus can theoretically even achieve “triple win” effects if improvements are achieved not just in one but in all three sectors (European Commission 2012).

Below, we show examples of different methodologies that have been drawn up to implement and test the nexus approach on the ground.

UNECE: The Role of the Water-Energy-Food Nexus in the Context of Transboundary Water Management

The WEF nexus was selected as one of the thematic areas of work under the UNECE Water Convention for the 2013–2015 program of work, particularly for the investigation of the Transboundary River Basin Nexus Approach (TRBNA) in the catchment of the Sava River (de Strasser et al. 2016). The TRBNA methodology consists of six steps as illustrated in Fig. 7.

Water-Energy-Food Nexus and Sustainability, Fig. 7
figure 2215figure 2215

Schematic of the six steps with inputs and outputs (de Strasser et al. 2016)

Full size image

Steps 1–3 include the preparation of a desk study of the basin, which will be used for the more in-depth analysis of nexus interlinkages in steps 4–6, where stakeholders are actively involved (de Strasser et al. 2016).

The Sava River Basin has a total area of 97,713 km2 and about 8.1 million inhabitants. It is partially situated in Bosnia and Herzegovina, Croatia, Montenegro, Serbia, and Slovenia, as well as a very small part of Albania. The countries achieve a significant share of water, hydropower, land area, and economic activity from the basin, for example, electricity generation capacity amounts to 53% or 76% of thermal power plants (United Nations Economic Commission for Europe UNECE 2016). The scope of the TRBNA in the Sava River Basin approach was to advance transboundary cooperation through nexus-based management of the Sava Basin’s resources in a way that Sava countries can exploit many potential benefits (United Nations Economic Commission for Europe UNECE 2016). The benefits worked out under the nexus approach are displayed in Fig. 8, comprising economic benefits, social and environmental benefits, regional economic cooperation benefits, as well as geopolitical benefits.

Water-Energy-Food Nexus and Sustainability, Fig. 8
figure 2216figure 2216

The benefits of transboundary cooperation on the nexus issues in the management of the Sava Basin’s resources (United Nations Economic Commission for Europe UNECE 2016)

Full size image

This method has been applied in several watersheds in Europe and Central Asia and is being refined further with every case. Overall the iterative process of desk studies with stakeholder interaction makes this methodology very hands-on and ensures that international expert knowledge is contrasted with national expert perception. One challenge is the selection of national expert which come from all countries of the rivershed and from various ministries within each country. In many cases this is the first time that this group of people comes together requiring the establishment of a baseline vocabulary to allow for a fluid transdisciplinary communication, a step that is, unfortunately, often ignored.

In terms of addressing the concepts of water, energy, or food security, the methodology is rather vague and not explicit. The benefits assessment could however provide a tool for looking into the aspect of security more in depth.

UNU-FLORES: Interlinkages Between the Water-Energy-Food Nexus and the Water-Soil-Waste Nexus

As an immediate response from the scientific community to the major outcomes of Rio+20, the United Nations University Institute for Integrated Management of Material Fluxes and of Resources (UNU-FLORES) was established in December 2012 in Dresden, Germany. Its main mandate is to further the approach of the water-soil-waste (WSW) nexus.

At the “International Kick-off Workshop: Advancing a Nexus Approach to the Sustainable Management of Water, Soil and Waste” in 2013, the WSW nexus was hence described: “The Nexus Approach to environmental resources’ management examines the inter-relatedness and interdependencies of environmental resources and their transitions and fluxes across spatial scales and between compartments. Instead of just looking at individual components, the functioning, productivity, and management of a complex system is taken into consideration” (UNU-FLORES 2015; Avellan et al. 2017).

As the WEF nexus considers the wide field of securities, the WSW nexus tries to focus on a systems perspective of the interactions between selected resources that support water, energy, and/or food security. The sustainable management of these resources, namely, water, soil, and waste, is considered key in achieving security. Such economic growth and increase in gross domestic product leads to the generation of waste or by-products, along with contamination and eutrophication of water resources. According to estimates by the United Nations Food and Agricultural Organization (FAO), 222 million tons of food are thrown away every year globally. Resource efficiency, the integration of environmental parameters, and social balance in economic decisions “pay off,” suggesting that more can be achieved with less. The use of treated wastewater (waste compartment) as irrigation supply (water compartment) for food production (soil compartment) is considered a prime example for the assessment of WSW nexus interlinkages at the environmental resource level but also for its effects on the governance level (see also Fig. 9).

Water-Energy-Food Nexus and Sustainability, Fig. 9
figure 2217figure 2217

Exemplary interlinkages between the resources water, soil, and waste. (Design adapted from UNU-FLORES, content based on R. Lal (2013))

Full size image

As water is included in the WEF and the WSW nexus, the basin scale is of importance in the discussion and different nexus-related research, some also including ecosystems or climate (Lawford et al. 2013; de Strasser et al. 2016; Karabulut et al. 2016). The WEF nexus has not yet come to a common understanding regarding the scale of assessing water, energy, and food interlinkages. What we know is that the different interlinkages of the WEF nexus are not fully understood on all scales (Hoff 2011), that it is not clear how to implement a nexus across scales (de Strasser et al. 2016), and that we need to find methods to connect these various scales (Endo et al. 2015). In order to provide a clearer picture for the system of the WSW nexus, Avellan et al. (2017) proposed the benefit-shed, which refers to a geographic area where at least two resource systems overlap and thus form the WSW system. The analysis of physical interlinkages within this system must aim to reveal benefits through increased resource use efficiency.

A distinct methodology for assessing securities has not been developed so far, but common risk assessments, environmental impact assessments, or sustainability impact assessment can be readily applied to each of the resources and the WSW nexus system as defined by the benefit-shed. This could also be linked to the benefits assessment of UNECE as described above providing a direct link between the WSW nexus and the WEF nexus.

Interlinkages Between the Water-Energy-Food Nexus and the Minerals-Energy Nexus

There are also strong interlinkages between the water-energy-food nexus and minerals-energy nexus according to McLellan (2017). This shall be illustrated using the example of the sand extraction in South East Asia, particularly Vietnam.

So far, sand in Vietnam has been extracted only by dredging from rivers as the country does not have other natural sand resources. This has led to enormous environmental impacts in the last few years, including a significant increase of the flood risk due to the altered hydromorphological structure of the rivers, which (a) resulted in a higher flow velocity and thus provoked increased risk of erosion in the rivers and (b) massive geotechnical problems with regard to the slope stability of the rivers and the related infrastructure. For this reason, there are river sections in which sand extraction has already been completely banned. The situation has led to a four or five told increase in the construction sand prices.

A government report from the Department of Construction Materials in the Vietnamese Ministry of Construction, issued in August 2017 and based on statistics from 49 provinces and cities, indicated that by end of 2016, there have been issued permits for the mining of 691 million m3 of sand and gravel. According to information from the Ministry of Construction in Vietnam, the domestic demand for construction sand between 2016 and 2020 is estimated at around 2.1–2.3 billion m3, while the country’s total sand reserves are just about 2 billion m3. With this rate of sand consumption in Vietnam, the country will run out of sand as building material by the year 2020. But this is just one side of the problem. Scientists from the Institute for Climate Change at the Cần Tho University recently pointed out that unbridled dredging for the sand extraction has already created deep holes in the Mekong River and it is causing massive land subsidence in the Mekong Delta. Due to land subsidence, the Mekong Delta loses around 500 hectares of land every year, and hundreds of families lose their homes and agricultural fields. It has also been noted that in the near future, once all 11 dams for water and energy supply on the upper Mekong are completed, there will be no alluvial sediment transport into the delta anymore. If the dredging continues at the operational sites and further pits become accessible, one-third of the Mekong Delta will disappear by 2050, resulting in irreversible environmental impacts in terms of flood risk, land subsidence, and biodiversity.

Meanwhile, the Mekong transports about 20 million t/year of sediment in the direction of the Mekong Delta, where it has been intensively used for decades for sand extraction. Nowadays, the volume of sand dredged from the Mekong River is twice as high as the sediment material delivered by sediment transport in the river. This has serious consequences not only for the ecosystem but also for living conditions along the river. Massive erosion has started, combined with land subsidence and slope instabilities. The river morphology has changed due to the dredging; the spawning grounds of the fish have shifted farther away, so that also the food provision by fishing is affected. For example, both tributaries of the Mekong, Tiền and Hậu, were deepened 5–7 m since 2008. The river level depletion accompanying the extraction of sand has an impact on agriculture: sludge and fine material are no longer reaching the agricultural land, resulting in a reduction in soil productivity. The overexploitation also has negative consequences for the environment and people in the sand extraction areas: in the Mekong Delta and other coastal areas of Southeast Asia, the sand extraction is already causing groundwater depletion and land subsidence. As a result, seawater penetrates further and further into the hinterland and spoils drinking water, agricultural fields, and soils (Fig. 10).

Water-Energy-Food Nexus and Sustainability, Fig. 10
figure 2218figure 2218

Impressions of the Mekong Delta including effects of sand dredging

Full size image

Sand extraction is also a common cause of shore and coastal erosion, making them more vulnerable to natural disasters such as floods, storm surges, or tsunamis. For instance, intense sand extraction in Sri Lanka worsened the effects of the tsunami in 2004. The focus of the An Giang Province in Vietnam recorded an increase in landslides and slope breakdown, which in 2017 caused provincial authorities to issue landslide warnings for the first time. In An Giang, the provincial authority identified 51 endangered river sections, with a total length of 161,550 m (DONRE An Giang 2017). Finally, this affects the food and energy provision in the catchment area. The Mekong River cannot provide its ecosystem services anymore in terms of food and energy to its full extent due to overexploitation of the natural capital.

Conclusions

The nexus approach provides a tool for the implementation of the SDGs as the main scope is defragmentation and consideration of the demands of all sectors and stakeholders, as well as the recognition of the demands of the ecosystems as part of the natural capital.

The WEF nexus intends to equitably achieve water, energy, and food security. This is considered key to achieve the agenda 2030 and thus sustainable development. For now, a handful of approaches to implement the nexus approach on the ground exist (more than what we have illustrated in this entry). In all cases the intention of addressing securities is present although not explicitly and probably forcefully enough. In general, the challenge still exists of assessing and interpreting the interlinkages of resources and acting upon these findings to achieve security in all fields at all scales, local, national, regional, and global.

In the near future, teaching the WEF nexus will be part of the curricula in higher education as one framework for the implementation of sustainability using a defragmentation tool, e.g. the teaching-research-practice nexus (Schneider et al. 2018).