We found in trend 1 that the predominant topic on WEF nexus research was related to water issues and security in natural resource use. Figure 4 shows the topics with the highest frequencies in data analysis. The analysis is divided into four quadrants with thematic clusters. For example, the topics of biofuel, renewable energy, and cost-benefit analysis are shown in yellow. In green cluster topics on water-related issues linked to agriculture and irrigation predominate. Food security, climate change, and sustainable development-related topics are grouped into a light blue cluster. Finally, topics in the clusters colored purple depict issues such as resource planning, urban areas, and urban planning.

Biofuel production is used as a prime example of water-energy-land/food interactions that unfold as synergies or compensations, as well as the competitive usages of land-water that take place in its production (Mwale and Mirzabaev, 2015; Rulli et al., 2016; Bellezoni et al., 2018; Ghani et al., 2019; Lazaro et al., 2021a). Biofuel is considered a pilot project for the successful implementation of a nexus approach (Benites-Lazaro et al., 2020). Importantly, this research on the WEF nexus has witnessed the emergence of a range of studies aimed at understanding (and sometimes attempting to quantify) the consequences of an eventual expansion of biofuel production on WEF resources. Thus, the initial focus of WEF nexus research concentrated on agricultural production links on different scales, from watershed studies to broader regions, such as resource exports (e.g., virtual water) between countries (Rulli et al., 2016; Moioli et al., 2018; Munoz Castillo et al., 2019). Studies have shown that water is the limiting component of agricultural production within the WEF nexus, and its use has been overlooked without considering adequate management, often prioritizing other nexus sectors, such as the production of biofuels (Smidt et al., 2016; Rodriguez et al., 2018; Benites-Lazaro et al., 2020).

Figure 5 shows trend 2 of the topic evolution in the 2017–2018 period, in which period, following trend 1, topics related to water issues as well as sustainable development are predominant. Other topics follow this tendency, for example, agriculture and land-use, ecosystem, and food security. Studies have emphasized that the WEF nexus approach has played a particularly prominent role in supporting the efficient implementation of the SDGs and promoting the green economy as a guiding principle for maintaining economic growth (Hoff, 2011; Giupponi and Gain, 2016; Terrapon-Pfaff et al., 2018; Simpson and Jewitt, 2019; Olawuyi, 2020). The green economy is considered the “nexus approach per excellence” (Brears, 2018), it seeks to unite under a single banner of the entire list of economic policies relevant for sustainable development, and it proposes to go beyond sectoral solutions and actively address the WEF nexus security in order to reduce access-inequalities of water, energy and food (Hoff, 2011; FAO, 2014; Biggs et al., 2015).

Studies have showed the importance of the interdependence among water, energy, and food systems by considering the WEF nexus as essential and intrinsic elements to human development and sustainability (Biggs et al., 2015; Simpson and Jewitt, 2019; de Andrade Guerra et al., 2020). The WEF nexus is a cross-cutting approach that through an interactive process can guide sustainable pathways to resource security and achieve the SDGs (Benites-Lazaro and Giatti, 2021). Its operationalization outcomes and the interactions of these basic resources could alleviate other issues, such as health, climate change, and biodiversity loss. The nexus approach is linked to SDGs, namely SDG 2 (zero hunger), SDG 6 (clean water and sanitation), and SDG 7 (affordable and clean energy), with synergies to SDGs 1 (no poverty), SDG 3 (good health and wellbeing), SDG 5 (gender equality), SDG 8 (decent work and economic growth), SDG 10 (reduction of inequality), SDG12 (responsible consumption and production), SDG 13 (climate action), SDG 14 (life below water), and SDG 15 (life on land). Therefore, the nexus approach can support sustainable development, with a focus on trade-off reduction and maximizing additional benefits or synergies that outweigh the costs associated with greater integration across sectors.

Figure 5 also shows the predominant topic of food security. Current studies on the driving forces of the WEF nexus in food production have focused on different scales and methods (Kajenthira Grindle et al., 2015; Li et al., 2019; Zheng et al., 2022). For some proponents, because food production consumes a lot of water and energy, the food dimension can be regarded as the center of the WEF nexus (FAO, 2014; Zheng et al., 2022). Other studies related to food security from the WEF nexus perspective have discussed the competitive uses of natural resources such as land and water for food or energy production, specifically biofuels (Rulli et al., 2016; Benites-Lazaro et al., 2020). These studies uphold energy, food and water security as being closely related to complex environmental, social, political, and economic matters.

Figure 6 shows trend 3 (2019), which emphasize topics such as governance, ecosystem, sustainable development, resource management, policy making, and decision making. Some studies refers to the nexus as governance concept that seek integrate resource management and sectors across policies and regulations to promote sustainability and better resource allocation (Kurian and Ardakanian, 2015; Weitz et al., 2017; Märker et al., 2018; Urbinatti et al., 2020). The nexus approach promotes policy integration and coherence by identifying optimal policy mixes and governance arrangements across nexus sectors (Weitz et al., 2017). It perceives integration and interdependence across various sectors as a fundamental step in ensuring resource security in the global context of increasing and competing demands (Artioli et al., 2017; Weitz et al., 2017).

However, implementing integrative governance can be challenging in many countries where institutional capacity is limited, and where there is a prevalence of conventional actions and policies characterized by decision-making in “silos” (which favors isolated sectors) (Weitz et al., 2017; Pahl-Wostl, 2019). For example, the study by Benites-Lazaro et al. (2020), which analyzed the Brazilian case, showed that nexus governance challenges are only partially considered in government structures, and their implementation remains a challenge in any fragmented institutional setting. Silo regulatory solutions prevail, and the tradition of planning and governance has been maintained in sectoral dynamics. The difficulty of each sector in implementing its own objectives is aggravated not only by the lack of connection between sectors, which in practice are already interconnected but also by the limited institutional capacity of institutions. Pardoe et al. (2018) showed that the Tanzania National Adaptation Plan of Action (NAPA) was an important milestone toward a change in sea levels in the integration of climate change into sectoral policies and plans. However, Pardoe's study shows that crucial cross-sectoral collaboration to implement climate change mitigation and adaptation strategies remains limited due to institutional challenges, such as power imbalances, budget constraints, and an entrenched-silo sectoral focus. Another study by Stein et al. (2018) described the interactions of the WEF system and the actors that influence these systems in the Upper Blue Nile region of Ethiopia, showing that the stakeholders in each WEF sector are not isolated from each other but rather embedded in hierarchical structures. These centralized governance structures can help explain why coordination challenges persist despite the cross-sectoral relationships among them, and also demonstrate the challenges in the governance of WEF systems.

The nexus approach focuses on policy coherence and integration. This is the systematic and dynamic identification and management of trade-offs and synergies between policies across sectors (Lazaro et al., 2021a). Existing studies show that “policy coordination” between various stakeholders, at all levels in general and at the local level in particular, governing the water-energy-food nexus is the key to promoting equitable allocation and access to the WEF (Sharma and Kumar, 2020; Rasul and Neupane, 2021). However, the effort to reconcile the fundamental objective of policy coordination and integrated governance in the WEF sector is in progress, and many questions about policy applicability, solid legal structures, and the political performativity of nexus thinking remain unanswered (Lazaro et al., 2021a).

Previous studies, such as Sharma and Kumar (2020) describes that policy coordination among all WEF nexus sectors, actors, and at all levels (multi-scale sector and multi-actors) is the key to promoting equitable resource access and allocation. To this end, legitimate governance with robust legal structures and effective stakeholder participation in the governance of nexus sectors is necessary to provide equitable resource allocation. In a similar vein Hagemann and Kirschke (2017) emphasizes that governance to promote synergies and mitigate trade-offs arising from resource constraints within the WEF system requires actor constellations and heterogeneous institutional frameworks that can vary depending on the context and phase of the political process. Mainly, with respect to the policy and decision makers, Mohtar and Daher (2016) refer to a lack of access to a set of comprehensive tools that: i) correspond to the nature of the nexus, they are multi-stakeholder and multi-scalar from local to regional, national, or global, ii) are capable of defining and quantifying the interconnectivity between WEF resources, and iii) are capable of including integrated and holistic management strategies to address planning for the allocation of these resources.

Policy coordination and harmonization of objectives for WEF nexus policies is, therefore, a daunting task that requires the involvement of key stakeholders, acknowledgment of different perspectives and priorities, and development of a shared understanding of what needs to be achieved (Rasul and Neupane, 2021). Hoolohan et al. (2019) suggest that integrating different forms of knowledge, such as rigorous analysis of case studies, stakeholder interviews, and agent-based modeling, can contribute to decision-making and policy. Thus, governance analyses should refer to different types of problems instead of focusing on single cases and abstract analyses. This facilitates the transfer of results to various contexts, and we can only find answers if the call for inter-and trans-disciplinary research is taken seriously, going beyond the sheer knowledge of any individual researcher. In addition, nexus approaches provide a concrete framework for the ongoing learning property of complex adaptive systems, thus involving social actors from different areas and organizational levels.

Figure 7 shows trend 4, in this period we identify studies applied to different scales, mainly there increasing research of the nexus at urban and city scales, and coupled topics such as circular economy, waste and WEF nexus, resilience, and smart cities. For example, in the circular economy, and waste–WEF nexus, an alternative to the current economic model, the circular economy is directly linked to a more sustainable development and has as its focus on the efficient use of resources and the minimization of waste generation, seeking to maintain the flow of material and energy at their highest level and for a maximum time (Geng et al., 2019). A circular economy can generate WEF co-benefits and bring together intersectoral collaboration to generate solutions to contemporary problems, such as solid waste and wastewater (Puppim De Oliveira, 2013; Del Borghi et al., 2020). The circularity of these streams could be expanded by connecting them with other sectors, further providing more opportunities for WEF provisioning and security. In this regard, a circular economy is intrinsically related to the WEF nexus approach, as both aim to contribute to reducing environmental degradation and its effects on resource security and climate, while promoting economic growth (Laso et al., 2018; Lehmann, 2018). As for the WEF nexus logic, systemic changes are needed for a transition from linear to circular systems to have a larger impact on WEF securities, requiring efforts at different levels of action and with the involvement of national, regional, and local government authorities (Ghisellini et al., 2016).

Driven by such integrated approaches, economies may benefit from a transition toward a circular economy that uses renewable resources and designs cyclical and efficient systems for provisioning WEF. Decentralizing waste management saves energy, water, land, and emissions, and reduces material waste. Thus, curbing food and water waste will contribute to lowering the overall energy use. Therefore, the circular economy is well suited to dealing with material supply risks, which are particularly pertinent to WEF security. For example, Lazaro et al. (2021a), have described that the linear agricultural economy can be transformed into a circular agricultural economy by minimizing water and energy consumption in food production, by using modern irrigation techniques, and reusing and recycling the agricultural waste in the form of biofertilizers. Some initiatives on the circular economy described by the bioenergy sector in Brazil are in the use of by-products as inputs for cogenerate electricity and the reuse, recovery, and recycling of materials and energy such as water reuse management, effluent management, use of vinasse as fertilizer, and crop rotation with grains that provide sugarcane productivity benefits (Lazaro et al., 2021b).

The study by Lehmann (2018) showed three specific cases on the implementation of circular economy and the urban nexus approach relating to energy, water, food and waste/material flows. Pekanbaru, Indonesia, the city implemented the project “New Landfill: Solid Waste to Energy Project.” The project entails the improved management of the sanitary landfill and the installation of an efficient methane gas collection and energy production system. Naga, Philippines, using the urban nexus approach, implemented a system for the production of energy from wastewater in the form of biogas and the reuse of treated wastewater for irrigation in agriculture. The urban nexus project in Nashik, India, focused on implementing efficient management and optimized use of energy and groundwater to limit the impacts of these scarce resources on farmers. This pilot project demonstrated a successful example of synergy and well-coordinated planning that improved resource productivity and economic gains from energy efficiency resulting in lower energy bills.

The nexus approach and circular planning for WEF sectors can increase resource flow capacity, reduce consumption, optimize production at local and regional levels, and add value to the WEF supply chain. Such integration optimizes planning for the use of resources, contributing to greater efficiency in industrial processes and infrastructure development, with consequent reductions in carbon emissions and waste generation (Lehmann, 2018; Feng et al., 2020). Local, regional, and national organizations can promote integrated planning through circular economy principles and the WEF nexus approach, focusing on improvements at the micro-meso-and macro-scales. Individual businesses (e.g., micro trades) can gain efficiency through internal circular models (e.g., material reuse). There are many opportunities for a more integrated economy at the meso level (e.g., industrial symbiosis). Finally, connections at the macro level, such as national energy or climate policies, can consolidate opportunities to further expand integration initiatives across the WEF sectors to combat climate change. Thus, expanding the nexus approach at different scales, and focusing on the impacts on the supply of scarce resources and the pressures exerted by climate change requires the involvement of stakeholders at different levels of action and with the engagement of government authorities at all levels.

As represented in Figure 8—trend 5 (2021 period), studies mainly show that urbanization and its links with climate crisis and global environmental challenges have made the WEF nexus approach a key element within debates on natural resource management, policy, and governance. Responding to the unsustainability challenges ahead becomes ever-more urgent and will require changes in the way societies manage and consume their resources. The nexus concept has become increasingly important in the urban context (Artioli et al., 2017; Lee et al., 2017; Covarrubias, 2019). Most of the urban population and consumption are concentrated in cities, which are dependent on hinterlands for WEF to sustain urban activities. Furthermore, the supply disruptions and immediate effects of COVID-19 on the provision of water-energy-food at the urban scale were aggravated in this pandemic context (Al-Saidi and Hussein, 2021).

With the projected growth of the urban population and consumption, the demand for natural resources will increase, stressing WEF systems. This urban demand for resources results in tension with neighboring communities, resulting in unwanted environmental impacts. Thus, we expect that a growing concern about the urban context will have reflect on the topics explored in the WEF nexus literature, which has historically had its origins in the agricultural sector, such the WEF nexus of biofuels discussed above. Therefore, a better understanding of the interests and institutions behind urban nexus research could help highlight and increase capacities to make changes and foster governance at the local scale, with the ultimate goal of increasing WEF security.

The transition from studies on the rural to the urban WEF nexus is therefore understandable and justified by the fact that cities are supported by resources coming mainly from rural regions, located far from consumption centers. Cities are often characterized by unsustainable patterns of consumption and production, which contribute to environmental degradation and injustices (Amaral et al., 2021). Urban demand for resources results in tension with neighboring communities, which exacerbates unwanted environmental impacts, especially climate change. In this regard, the WEF nexus approach can contribute to a better understanding of the potential connection between cities and rural areas, increasing capacities to promote changes and fostering governance at local and regional scales, with eventual positive impacts on WEF systems (Seitzinger et al., 2012; Artioli et al., 2017).

Our study identifies that the literature on the WEF nexus has been extensively outlining the failures in the planning and management of these resources, stressing the importance of considering both the interdependence between sectors and their indirect and transboundary effects. Motivated by the IWRM approach to water management and the repercussions caused by the Bonn 2011 Conference, researchers and policymakers have been striving to refine and spread the nexus approach to understand the trade-offs and synergies in the supply and demand of WEF resources. While it has potential strengths, the understanding, diffusion, and application of this framework also face challenges, particularly with respect to transitioning from its theory and modeling to real-life applications.

Our review points to the existence of different approaches for the WEF nexus that present variations according to the focus component under analysis, with initial focus on the water sector. We also identified the evolution of nexus approaches over time and their application to different scales, starting from an agricultural context to a more urban approach, and sometimes including elements that go beyond the three basic resources of the WEF nexus. Such evolutions in the application of the concept have a common focus on a transition toward more integrated planning for WEF sectors, regardless of the motivating factor for the analysis. The shift from silo thinking to systemic and integrated planning for WEF requires a complete restructuring of institutions and the way in which society views, exploits, reuses, and disposes of WEF resources. Therefore, it is instructive to examine trends in WEF nexus research, in terms of predominant topics to discover how the evolution of this approach may gradually influence the shift to systems thinking with its application to different scales.

Through the LDA method applied to examine a large amount of information in the literature and map its thematic landscape, it was possible to identify how some studies on the WEF nexus, initially focused on technical aspects to better understand the trade-offs between the sectors. For example, bioenergy production and its impacts on WEF security have begun to include governance elements for these sectors, in addition to examining the institutional and social aspects of the SDGs. These topics are important for a systemic analysis of the impacts of natural resource exploitation, production, and supply but are not fully representative of the broad solution. Thus, an emerging and relevant range of research has been neglected, as the focus was on understanding the impacts of WEF resource supply rather than demand. More recently, nexus frameworks applied at the scale of metropolitan regions and cities have driven the shift to approaches that include other components that directly or indirectly affect WEF systems, such as ecosystem services, waste management, circular economy, mobility, and smart cities.

Moreover, our research approach identified the thematic trends in the literature on WEF nexus post the 2011 Bonn Conference. For example, there is a fast-growing research cluster around topics such as sustainable development, urbanization, renewable energy, climate change, and circular economy. Because some of these topics have been comparatively small in the past, WEF nexus researchers may want to give them more consideration in the future. We also point out that with the inclusion of a chapter on cities in the fifth report of the Intergovernmental Panel on Climate Change, the trend is for this topic to dominate WEF nexus research, as cities are major contributors to the demand for WEF, largely supplied by adjacent regions and with significant negative impact on supply-chain emissions. However, we do not suggest that the fastest growing topics should be the focus of future research, as renewable energy (e.g., biofuels) and sustainable development have already been considered. Instead, our topic mapping exercise is intended to draw attention to relevant issues in discussions on how the nexus approach can be applied to different resources and at different scales through the development of case-specific methodologies and policies.

An IWRM review points out that the integrated water management concept has existed since the early 1990 decade, but has a dubious implementation record, without being critically evaluated. The criticism focused on the fact that contemporary publications that promoted the IWRM approach were not able to identify an implementable process for integration, with difficulties justifying the use of the concept (Biswas, 2009). The main reason for this was the “almost universal popularity of a vague, indefinable, and inexplicable and non-implementable concept” (Galaitsi et al., 2018). Similarly, the WEF concept appears to struggle with the same issues of coherence.

Despite the evolution of the topics, WEF nexus research has presented some difficulties in defining universal approaches, methods and tools in the field, in addition to a deficit in the inclusion of socioeconomic analyses, particularly on the actors and institutions that shape access, distribution, and use of WEF resources (Newell et al., 2019). This difficulty of universalization lies in the fact that applied WEF nexus frameworks require that the structure of WEF systems be sized for specific cases, aiming at different evaluations and applications, as well as be useful for policy implementation and decision making. The availability of complete and relevant data also poses a challenge for the practical implementation of the WEF nexus on any scale of interest, which is viewed as a weakness by some researchers (Simpson and Jewitt, 2019).

Ideally, the WEF nexus literature would provide a platform for converging multiple streams of research, identifying linkages and complementary policies. For example, ecosystem services promoted by nature-based solutions, such as urban agriculture, strategically located in regions with high demand for WEF and low local supply, could provide residents with the option to purchase (or even produce) these resources locally. This would contribute to changes in consumption habits in the medium to long term, with immediate effects on transboundary demands for WEF and their associated emissions. This suggests an important avenue for future research toward integrating policies for land use, urban development, circular economy, renewable energy, and WEF demand and supply planning for additional benefits at different scales for resource security instead of focusing on sector-specific options alone.

Therefore, on the one hand, more cooperation and integration between WEF sectors as well as between different governmental levels is needed to promote the positive effects of the nexus approach in the planning of food, water, and energy systems. In practice, we need to develop multilevel sector integration to better understand the policy challenges of applying a conceptual idea in the real world, in the form of. learning-by-doing. Advancing the desired sustainability in the use of scarce resources should not necessarily depend on public policies and initiatives, and be better understood, designed, and disseminated by researchers and decision makers. On the other hand, there is the need to study the results of these practical trials to advance the science on how the nexus approach can solve issues that emerge in its application. It would be a process of going back and forth from science to policy and vice-versa. Thus, the two-way linkage between science and nexus policy can be improved by further digging into the science of nexus by learning from its application, which tends to have results very dependent on the context. In this sense, despite its limitations, the evolution of the applications of the nexus concept over time has value in allowing it to be adapted to different perspectives and interests, enabling easy inclusion of emerging Research Topics.