Bridging the gap between the water-energy-food nexus and compound risks

The water-energy-food (WEF) nexus is a concept and approach to examine the interactions of water, energy, and food resources. Similarly, compound risks are a set of risk types that consider multiple connected factors that amplify risks. While both concepts are promoted as approaches to move beyond silos and address complex problems in environmental governance, there has been limited exploration of their overlap. Our study integrates these two approaches for more holistic assessment and management of resources in the context of climate risks. We examine the connections between the WEF nexus and compound risk in two ways. First, we review the literature to identify previous conceptual connections between the WEF nexus and compound risks. Second, we review seven case studies with WEF nexus interactions and compound risks to identify how the two approaches might be considered in practice. Our results demonstrate that there is limited, though not non-existent, integration of the two concepts in both the theoretical literature and in the case studies. The four of the seven cases that do show some level of connection in


Introduction
The water-energy-food (WEF) nexus and compound, complex, and cascading (hereafter referred to as compound) risks are two parallel movements that seek to move beyond silos for more integrated assessment and management of natural resource systems.The WEF nexus approach examines the physical interconnections between the three resources and argues for integrated governance to link them together within decision-making and policy frameworks.Compound risks are types of risk that move beyond singular climate events and instead consider how risks may emerge from multiple climate events or from sequential occurrence of such events.Both concepts seek to increase understanding of dynamic natural systems, reduce unintended consequences, increase resource security, increase efficiency through positive spillovers, and lead towards greater sustainability of the human-environment system.Despite the similarity in goals and in the effort to move beyond silos, the opportunity for intersecting the WEF nexus and compound risk literatures has not yet been explored.The WEF nexus considers simple forms of risk, mostly through risks to water, energy, and food security; compound risk considers the risk of climate events to water, energy, and food resources independently, without consideration of cross-sectoral interactions.Yet linking the two concepts together can further break down silos between resource sectors by investigating compound risks within WEF nexus connections.Previous research either focused on simple risk within the WEF nexus or considered compound risk indirectly through cascading events.Therefore, this paper builds on previous study to explicitly integrate compound risk and WEF nexus governance approaches for improved and more holistic assessment and management of humanenvironment systems (see 'Conceptual integration' subsection).We look at the connections between WEF nexus governance and compound risk in two different ways-first, through a review of the analytical and theoretical literature for both concepts and second, through the examination of seven case studies.Our findings from the case study analysis show that four of the seven cases demonstrate moderate effort to connect compound risk and the WEF nexus in practice, but these developments remain in the initial stages and further efforts are needed in practice for the consideration of compound risks in WEF nexus governance systems.

WEF nexus
The importance of the WEF nexus approach emerged in the context of changing social structures and climate, which increased pressure on existing systems and highlighted tradeoffs and interactions between sectors [1].The WEF nexus integrates the multiple sectors and stakeholders to consider trade-offs and synergies between those sectors' sustainability [2,3].Nexus thinking addresses externalities and prioritizes system efficiency and sustainability over the productivity of individual sectors [4].It has been conceptualized as an analytical tool, as a normative conceptual framework for policy integration, and as a discourse for framing problems of resource management [5,6].The WEF nexus has become increasingly important in climate-related literature over the past few decades [7,8].The literature includes a diversity of different methods of analysis, though research methods have focused on quantitative over qualitative approaches [9], leading to calls for more investigation on qualitative and comparative cross-case analysis [6].Research on WEF nexus interactions can be interdisciplinary, involving ecological, physical, socioeconomic, and political factors [8].Due to the connectivity of the sectors, any issue in management that impacts one sector has the potential to impact the others [3].
The nexus approach is situated in broader socioeconomic, political, and environmental contexts.It is especially important given the existing and projected scarcity of natural resources due to the magnitude and uncertainty of various stressors.Climate change has the potential to affect all three sectors within the WEF nexus, impacting water availability, energy supply and demand, and food production capacity [4,10].The WEF nexus seeks to maximize synergies, which can produce mutually beneficial outcomes, and to minimize tradeoffs, which could lead to potentially non-optimal outcomes [9] and exacerbate inequities in access to resources [11].Management of these resources through isolated sector approaches has the potential to lead to unintended consequences in related sectors, necessitating systems-level thinking [4].However, as energy and water sectors have hard, often centralized infrastructure that guides the management of those resources, whereas the food sector lacks hard or centralized infrastructure, differences in scales and infrastructure landscapes have influenced how these sectors are governed and contributed towards traditional management silos.
WEF interactions occur across both spatial and temporal scales.Thus, differences in temporal and spatial scales of water, energy, and food resources and decision-making institutions have resulted in challenges for WEF nexus integration.Much of the existing empirical literature tends to make simplifications by examining a single scale despite acknowledgement of the multiple scales at which the nexus exists, focusing on a single trigger causing a ripple effect on the system despite the possibility of multiple triggers, and omitting analysis of governance and policy issues [3,8].Governance in the WEF nexus is non-trivial, as sectoral management has historically been siloed and sectors are governed by different agencies across different temporal and geographical scales, and research on policy issues may be pivotal to implementation of the nexus approach [3].Considering the landscape of existing research on WEF nexus governance, future research should welcome interdisciplinary dialogue, methods, and application and directly examine how climate change increasingly challenges nexus connections [12,13].

Compound risk
In recent years, academic researchers and policymakers have paid increasing attention to compound, complex, and cascading risks in resource management and governance; we use here the term 'compound risk' to refer to this whole set of risks, since it is the most widely used.This attention builds on increasing centrality of risk as an organizing concept in climate action since the 2010s [14]; it has also been prominent in the disaster risk reduction literature [15].This set of risk types can be distinguished from simple risks, which are associated with single climate events or single types of climate events, but the terms within this set are not clearly or consistently distinguished, and the relations between them remain only incompletely explored.In addition, the phrase 'connected extreme events' has been proposed to describe this phenomenon [16].It is only in the Intergovernmental Panel on Climate Change (IPCC) Sixth (and most recent) Assessment Report (2022) that the terms are mentioned frequently (figure 1) and that the terms appear in the report's glossary.The summary for policy-makers of Working Group II in that report states that increasingly complex climate change impacts and related risks are difficult to manage, especially as multiple climate hazards occur at the same time, leading to interacting climate risks that may lead to a chain reaction across multiple sectors and locations.Cascading Cascading risks emerge from extreme weather/climate events which occur when an extreme hazard generates a sequence of secondary events in natural and human systems that result in physical, natural, social or economic disruption, whereby the resulting impact is significantly larger than the initial impact.
Source: IPCC 2022 Sixth Assessment Report, Working Group II, Chapters 1 and 16.
Chapter 1 of this report addresses this set of terms as a whole (see table 1).It recognizes that these risks are becoming more frequent and severe, and therefore merit attention, though it suggests that these risks are harder to model, and harder to attribute to climate change, than simple risks [17].It notes as well that these three terms are not sharply distinguished.The term 'cascading' is used in the report to indicate sequencing; it refers to risks or impacts that follow upon other risks and impacts in different regions or sectors, or that occur later in time; it has been linked with the concept of tipping points [18].The term 'compound' is used to indicate interactions, which might be simultaneous or sequential [19].The term 'complex' includes the notion of interactions, but also incorporates the nature of entire systems.Chapter 1 notes several dimensions of complexity, including 'the behaviour of complex systems, which includes multiple stressors unfolding together, cascading or compounding interactions, and non-linear responses and the potential for surprises.'These studies of compound risks examine the connections between several different risks.Among these, precipitation is central, whether in the form of excessive water and flooding or deficient water and drought [20]; pairings of climate risks are drought with heat and heavy precipitation with strong wind [19,21].Most research considers compound risks at the local scale [20], though it can extend to sub-national to national scales [22], and even to the global scale, in cases where cascading risks such as shocks to food systems spread across great distances [23].
Compound risk studies emphasize the importance of fuller understanding of compound risks to promote more effective decision-making and policies to reduce impacts; in this way, they resemble the recent attention to multi-sectoral dynamics, an approach to the complexities within coupled human-Earth systems which examines interdependences between sectors, with a particular emphasis on modeling [24].However, complex risk studies, like multi-sectoral dynamics studies, generally do not consider coordinating responses across sectors [16]; a few papers point generally to the connection with nexus approaches, though these suggestions remain weakly developed.One review of complex risk assessment notes that the examination of cascading and compound risks is cross-sectoral by nature and provides opportunities for nexus approaches [21], but does not include nexus governance in any of the four case studies it examines.Similarly, a study of cascading effects of climate change notes that water scarcity and food scarcity can be linked and suggests the importance of considering the nexus between water, energy, and food, but it does not include nexus approaches in its discussion of governance mechanisms to address such impacts [18].

Conceptual integration
From the literature, we analyze four aspects of the relationships between the WEF nexus and compound risk: similarities in bridging multiple systems, differences in the aim of each approach, potential benefits that arise from integrating the two, and limited number of instances of such integration.We discuss these aspects in depth here.
There are clear similarities between the WEF nexus and compound risk framing in the literature.Both are centered on the interconnections between distinct systems and breaking down silos.The WEF nexus does this through the consideration of synergies and trade-offs between the three resources, while compound risk does this through examination of multiple cause-effect relationships.Additionally, both address multiple systems by looking across different levels of spatial, temporal, and institutional scales, which requires more complex analysis that considers individual components and relationships.Furthermore, both literatures call for analysis and policy that integrate across different components and levels of systems.In the nexus, these components are interconnected sectors where stress in one sector may become the trigger for stress in related sectors.In the case of compound risk, these components include risks, hazards, and vulnerabilities that are proximate either spatially or temporally, in which a change in a specific driver may lead to increased risk across these risks.
The two differ, however, in terms of their goals.While WEF nexus policy aims for improved efficiency and optimization within a system, compound risk analysis aims for overall risk reduction.Nexus policy places a larger focus on day-to-day optimization of systems, whereas compound risk focuses more on extreme events with high levels of uncertainty; this demonstrates differences in time scales as well as focus.These differences may stem from the origins and development of the two approaches, as the WEF nexus was developed as a response to resource insecurities while configurations of compound risk emerged to address hazards.Additionally, nexus tools deal primarily with understanding the complexity of information, while compound risk may seek to characterize risk or develop policies aimed at improving decision making in practice.Furthermore, the WEF nexus specifically combines sectors (most often water, energy, and food) while compound risk links events (e.g.floods, landslides, wildfires).Finally, WEF nexus governance includes actors, institutions, and organizations from water, energy, food, and environment sectors that operate at multiple levels and scales, while governance in compound risk often happens within resource sectors.
Merging the WEF nexus and compound risk offers practical benefits.This integration could enhance the nexus' ability to address unintended consequences in more concrete ways and to mitigate issues of compound risks that may have been previously overlooked.The similarities and differences between the nexus and compound risk framings highlight the need for tools that integrate the two concepts.Both the WEF nexus and compound risk framings advocate for the design of more flexible and comprehensive policies and tools, which consider systemic connections and potential spillovers.These tools ideally coordinate potentially disjointed policies.As a result, policies that target one part of the interconnected system will not necessarily lead to adverse effects in other parts of the system.Given the WEF nexus goals of efficiency and optimization and the compound risk goals of risk reduction, integrating sector and risk policies together goes a step beyond integration within sectors and within risks.
This potentially beneficial integration is realized only in a small number of instances.Existing discussions of risk in the WEF nexus conceptual literature often emerge in response to visible manifestations of risk and primarily consider the potential contributions of WEF nexus approaches that can help to reduce resource insecurity risk in water, energy, and/or food sectors.For example, some WEF studies examine general risk directly, such as by examining how WEF infrastructure mediates the risk of climate change [25,26] and by conducting risk assessments of physical resources in WEF nexus systems [27][28][29].However, the few studies that mention compound risk specifically in the WEF nexus either considered compound risk indirectly [30] or focused on cascading effects [31,32].The United States Fourth National Climate Assessment report highlights interdependencies between multiple sectors, cascading risks, and complexity, yet does not explicitly consider compound risk within WEF nexus systems [33].Thus, our literature review demonstrated that there is limited discussion specifically of compound risk in WEF nexus governance.This gap may reflect the early phase of WEF nexus conceptualization centered around addressing physical resource insecurity [31,34] over addressing governance and institutional challenges, where risk might be more directly considered in policy and management [8].Similarly, the compound risk literature offers limited examination of how interconnected water, energy, and food systems might lead to compounding, complex, or cascading risks across resource sectors.The compound risk literature reviewed instead focused on risks within a resource sector, with no studies directly examining compound risks reaching across sectors.In sum, the similarities and differences between the WEF nexus and compound risk provide opportunities for integrating the concepts for improvement of assessment and management, despite the limited integration that has been done thus far.

Methods
We first conducted two literature reviews of WEF nexus governance literature and of compound risk literature.These reviews examined seminal early papers and recent literature.These literature reviews were not meant to be exhaustive, but representative of each concept.We then searched for papers that intersect between the WEF nexus and compound risk.In Web of Science, we used the following search string to capture the full set of compound risks: ABSTRACT, TITLE, KEYWORDS = (((compound risk) OR (complex risk) OR (cascading risk)) AND (food energy water nexus)).This returned a total of 59 results as of May 2023.We then manually examined the abstracts for the papers to screen for the intersection of the WEF nexus and compound risk.As stated previously, these papers generally discussed the nexus by considering the interactions between water, energy, and/or food resources and discussed risk through risk assessment, climate risk, and decision-makers' considerations of risk in their decision-making.Considering risk in the WEF nexus mostly consisted of general risks to water, energy, or food security; there was limited discussion of compound risk specifically.These results demonstrate the limited presence of compound risk in WEF nexus literature.Based on the limited results, we used our initial literature reviews of the WEF nexus and compound risk to identify parallels between them.We then integrated these two literatures to create a conceptual framework of the intersection between WEF nexus governance and governance of compound risk (figure 2).
Using case studies, we demonstrate the application of this conceptual framework.We selected seven exemplary WEF nexus case studies.Given that compound risks have been becoming more pressing with climate change only recently and the fact that nexus governance integration is relatively new, we focused our attention on case study policies since 1990.These cases were not intended to be exhaustive, but rather as representative of different configurations of WEF nexus governance.We propose that our number of cases (n = 7) is sufficient, in line with best practice for cross-case comparison that recommends a minimum of four cases in a study [35].Additionally, our cases span across four continents, include high-, middle-, and low-income nations, and span different geographical scales (city, country, water basin/international), indicating their broad coverage.Each case provides a rich understanding of the two concepts and comparing across them provides a landscape for generalizable themes [36].These case studies were examined using previous empirical studies that conducted research on WEF nexus governance and compound risk governance with a focus on the presence of these politics in practice and the degree of integration between them.Table 3 contains a summary, rated qualitatively where low indicates no robust evidence in the literature (few explicit mentions, clearly stated failures or limitations to success), medium if there was some mention of existence but no significant assessment of success in the reviewed literature (some mentions, some exploration in depth, and either no discussion of success or stated partial but limited success), and high if there were multiple mentions of existence accompanied with analysis on impacts in the literature.Using these empirical case studies and our conceptual framework developed from the literature, we triangulated across the case studies to identify key cross-cutting themes and recommendations for future integration of WEF nexus governance and compound risk in both research and practice.

Case studies
Table 2 presents a brief overview of each of the seven cases we examined in our study (figure 3).Based on our overview, the WEF nexus and compound risk governance face different challenges based on geographical scale.In this section we present three of the cases in more depth, one from each of the three scales in our study, to demonstrate WEF nexus and compound risk integration challenges: the region of the Mekong River basin, the country of Brazil, and the city of Phoenix, USA.Longer descriptions, including additional references to sources, are provided in the Supplementary materials.

Multinational case: Mekong River basin
Multinational cases like the Mekong River basin are most often characterized by cross-border rivers, which present not only compound risks in the forms of flooding and droughts, but also are essential sectors to be managed within the nexus given tradeoffs in river usage between food (for irrigation, fisheries), energy (hydropower), and water.The Mekong region faces additional challenges with socioeconomic development and projected population growth that is expected to place increased demand on nexus resources as climate change exacerbates river variability [37][38][39].
A review of literature on nexus governance in individual countries in the region suggests that crosssector governance is poor.For instance, analysis of Laos and Thailand reveals governance divided among sector-specific ministries with bureaucratic competition impeding cooperation.Nexus policies also tend to be reactive to events and public pressure rather than anticipatory, suggesting limited attention to risks [40].Similar issues appear in Cambodia, which has attempted to address siloing via the creation in 2015 of a National Council for Sustainable Development that seeks to promote integration across sectors.However, the influence of this council has been limited [41].
Coordination between countries on usage of river flow places an additional challenge for nexus governance.Power dynamics between upstream countries like China, which owns most upstream dams, and downstream countries create challenges for equitable river resource allocation [42].In an attempt to promote cross-country coordination, the Mekong River Commission (MRC) was created in 1995 between Laos, Cambodia, Thailand, and Vietnam with China and Myanmar as upstream observers.The MRC convenes heads of government and sector ministries to promote cooperation around issues including hydropower, fisheries, and flood control.However, literature analyzing the MRC suggests that it alone is insufficient to achieve all nexus governance goals [43].

National case: Brazil
Decreased rainfall attributed to climate change is expected to impact the country, especially in the northeast region.This decreased rainfall impacts agriculture and dam capacity, reduces energy reliability by increasing river volatility and therefore hydropower generation volatility, and pushes crop production toward crops that are irrigation fed rather than rain fed.Thus, risks in water security also lead to risks in food stability and energy reliability, demonstrating compound risks.Limited land and competing land uses necessitates coordination between agriculture for food, agriculture for biofuel production, and forest preservation that could help mitigate risks from flooding [44].
There are some policies in Brazil that address the interdependency of nexus sectors but implementation of these policies remains relatively weak.These policies include both cross-sector policies, such as the 2013 National policy on integration of farming, livestock and forestry and the 2017 RenovaBio policy, and national development plans, most notably a series of national plans and policies for adaptation, created in 2008, 2009, and 2016 [45][46][47][48].However, goals within these policies remain sector-specific and are implemented by separate institutions [47].In general, historically siloed governance has been difficult to overcome, preventing coordination [45,48].Further complicating coordination, the country's decentralized government leads to different levels of government being responsible for overlapping or competing tasks [47].
This lack of coordination has led to poor implementation and limited success of nexus policies.For instance, the country has attempted to increase the resilience of its energy sector due to risk from hydropower generation driven by river volatility.One such policy is the above-mentioned RenovaBio policy, which has attempted to shift toward increased use of biofuel having assessed the risk within the energy sector.This shift, however, requires increased water usage since sugarcane is relatively waterintensive to grow.The tradeoffs between water use for hydropower and biofuels are not addressed, and risks for the water and food sectors are not well considered, suggesting lack of coordination between agencies responsible for each type of energy source [48].
Table 2. Overview of the seven cases that were examined to identify WEF nexus challenges and compound risks.

Multinational cases
Tigris-Euphrates River basin, West Asia (Turkey, Iraq, Syria) Variability of river flow, which is expected to increase with climate change, leads to the dual risks of floods and droughts that impact the downstream countries of Iraq and Syria more than it will impact Turkey, which controls the river headwaters.Since the 1980s, there has been cross-country and cross-sector collaboration across all three countries and high-level, bilateral agreements have been in place since the early 2000s, although political instability in Syria and Iraq has hindered implementation.While these agreements have focused on mitigating risk of water shortages and protecting water quantity and quality, they have also attempted to address other aspects of the nexus by, for instance, increasing resilience of crops and efficiency of irrigation.
Hindu Kush region, Central-South Asia (India, Nepal, Pakistan, Bhutan, Bangladesh, Myanmar) Current and projected increased river variability and more intense monsoon-driven rainfall extremes will lead to increased risk of droughts, glacial outburst floods, and flash floods, while decreased surface water resources will increase dependency on groundwater resources.Social issues exacerbate nexus concerns, as much of the population is socially marginalized, and projected population growth will place further strain on already limited food and energy resources.Nexus policies in the region are the responsibility of national planning commissions, which provide support to ministries pursuing sector-specific goals and are therefore not well positioned to facilitate integrated governance.While most decisions are made at a local rather than basin level, there has been cross-border integration through cross-regional organizations and agreements.
Mekong River basin, Southeast Asia (China, Laos, Vietnam, Thailand, Cambodia) As with the Hindu Kush, the dual challenges of climate change and socioeconomic development will place increased demand on river resources.The basin is one of the most active areas for hydropower in the world, and the Mekong Delta, which relies heavily on irrigated water, serves as a food basket for the region.Within countries, coordination between nexus sectors is limited with governance vertically divided along ministry lines.While there is some integration and coordination across countries, success has been limited by political dynamics between upstream and downstream countries, with more powerful upstream countries simultaneously being the least vulnerable to climate change risks.

Brazil
Current and projected decreased rainfall driven by climate change has and will exacerbate issues related to energy reliability (as hydropower is the most common energy source), change in crop production from rainfed toward irrigated methods, strains on drinking water availability, and decreased ethanol biofuel production.Existing policies acknowledge nexus interdependencies, but integration of governance structures faces challenges associated with historical siloes and constraints around government structure, as different sectors are managed by different levels of the partially decentralized government.While risk considerations motivate some nexus policies, particularly in intrinsically intersectoral issues like hydropower and biofuels, tradeoffs in addressing risk are not well accounted for.

South Africa
Decreased water availability has and will continue to threaten agricultural productivity, food security, and energy security, as the country relies on coal for electricity generation, a process which requires water.Moreover, surface water resources in the area are difficult to replenish.Having faced severe drought with spillovers to the food and energy sectors, the South African government has created policies that acknowledge interdependencies between nexus sectors with the goal of achieving economic growth.Despite these policies, the existing siloed government infrastructure makes coordination difficult.Risk has mostly been addressed through sector-specific policies, leading to tradeoffs in risk between nexus sectors.
Phoenix relies on imported surface water from the Colorado River as well as groundwater and reclaimed water, all of which are highly energy intensive.Scarce water resources must be divided between urban uses and tribal communities as well as nearby agricultural and energy sector uses.The region has faced prolonged drought, leading to overallocation of river water and increased dependency on groundwater resources.While there exist a few sector-specific policies that present opportunities for cross-sector collaboration, coordination of governance structures is stymied by incompatible organizational structures and management processes across sectors, as well as a lack of trust and historical negative experiences.Risk considerations in nexus policies are largely focused on managing water scarcity.
(Continued.) Water demand is increasing with urban population growth, industrial and agricultural sector expansion, and increased fracking.Water in the region comes mostly from groundwater, which is non-renewable, and climate change will exacerbate existing water scarcity.The spatial location of resources as well as administrative hierarchies complicate cross-sectoral coordination as governing bodies for different resources often have non-overlapping areas of control.Communication is more common among organizations governing water resources but much rarer between nexus sectors and within the food and energy.While the risk of water scarcity, specifically in response to recent droughts, has spurred some adaptation policy, it does not necessarily lead to concerns around the food or energy sectors and hence does not translate to attention being paid to the nexus and associated risks.

City case: Phoenix
The Phoenix region is currently facing challenges with prolonged drought, which has impacts on agriculture as well as electricity generation, both of which are water intensive.With the city's population growing, these issues will be further exacerbated and increase the likelihood for compound risk impacts.As local surface water reservoirs are limited, the city has turned to alternative water sources, including ground and imported surface water, both of which require intensive amounts of energy for pumping groundwater and moving surface water [50].Energy is also needed in the area to move food from agriculture toward consumers [51,52].Some compound and nexus risk policies exist that address these connected challenges.The 2019 drought contingency plan provided a state-wide plan for the allocation of water cuts in response to shortages on the Colorado River and more long-term, the Arizona Department of Water Resources has periodically released plans for long-term water management goals, which consider food and energy needs [50,51].However, these policies face design flaws.For instance, shortages on the Colorado River have also impacted hydropower generation on Lake Mead, requiring shifts toward other energy sources.As a result, policies that aim to address risks within the water sector may have cascading impacts on the food and energy sectors, and there are limited policies addressing these spillovers.
Analysis of governance structures in the city reveal that there are low levels of coordination between Table 3. Summary characterizations of the seven case studies, including geographical scale, role of various sectors, existence of policies, and extent of integration.In the column 'Scale,' M refers to multinational, N refers to national, and S refers to sub-national.In the columns 'Sectors most prioritized' and 'Sectors most at risk,' W refers to water, E refers to energy, and F refers to food.Case studies are rated as low if there was no robust evidence in the literature, medium if there was some mention of existence but no significant assessment of success in the reviewed literature, and high if there multiple mentions of existence accompanied with analysis on impacts in the literature.with decision-makers across the local, regional, and state levels.The literature suggests that water stakeholders are more likely to coordinate with other sectors, but overall coordination is limited by differences in organizational structures; differences in decision making, policy, and management processes; and a lack of trust created by historical bad experiences [50,53].Table 3 compares the main findings across the case studies.These seven case studies provide examples of WEF nexus governance and compound risk in practice, highlighting similarities and differences.These cases demonstrate the wide-ranging challenges associated with climate change, nexus integration across sectors and levels of government, and considering both nexus and risk in policy.

Discussion
Examining the connections between WEF nexus and compound risk and applying this framework to examine case studies, we note three cross-cutting themes that can be categorized as follows: the case studies demonstrate limited evidence of WEF nexus and compound risk integration in practice, case studies document numerous challenges in integrating these concepts, and water stands out as the central sector of the nexus and as the sector most at risk across all cases.This final point suggests a possible way to start addressing the shortcomings discussed in the first two by focusing simultaneously on the relation of water to other sectors and of water risks to other risks.
First, there is only limited evidence in practice of the application of compound risk to address WEF nexus governance.This finding supports what we found in our literature review, as discussed above.Our case studies did not include examples where consideration of compound or cascading risk in management, planning, and policy has led towards governance decisions that considered water, energy, and food trade-offs and interactions.For example, compound risks are well known in the Mekong basin, namely how potential climate impacts on resource availability-especially water resourceswill be exacerbated by the social and economic conditions of the area.However, planning to address such risks does not consider connections between water, energy, and food.While knowledge of risks has perhaps spurred cross-country integration of water management in the Mekong region, it has not been sufficient to incentivize cross-sector collaboration either within or across countries.Similarly, there are limited examples in practice of the implementation of WEF nexus governance to address concerns around compound risk; cases that exemplified management and policy decisions that considered water, energy, and food trade-offs did not explicitly consider compound risks that might emerge from such trade-offs.For example, while policymakers in South Africa have coordinated across sectors in response to the current and future risk of water scarcity, emphasizing their awareness of the potential impact of water scarcity on food and energy sectors, adjustments in policies to mitigate the risk in specific sectors have not considered the compound risks and impacts within or outside individual sectors.
Second, there are numerous organizational challenges in integrating WEF nexus governance and compound risk policies in practice.Most notably, the lack of collaboration, communication, and coordination across WEF sectors constrains integration of compound risks into policy.Table 3 demonstrates the relative weakness of nexus governance across the seven case studies and underscores that even in settings with strong attention to compound risks in policy, integration between the nexus and compound risk is only as strong as the level of nexus governance.In the two examples of South Africa and Phoenix where policies target compound risk, these policies are limited by the lack of integration across WEF sectors in governance structures.For instance, the South African National Water Act of 1998 aims to holistically manage water to maintain a designated amount of reserved water to support human needs, including energy provision, but falls largely under water catchment management agencies that are not well integrated into other governance structures.In San Antonio, integration is weaker than both nexus governance and the extent of compound risks in policy.
Although not explicitly highlighted in the case studies, it is likely that WEF policies and compound risk policies require different types of governance structures and stakeholder expertise.As a result, WEF and compound risk policies may fall under the purview of different types of stakeholders, further challenging integration.These challenges are partly to the different goals of the WEF nexus and of compound risk approaches.
Finally, water management concerns are present across both the WEF nexus and compound risk in the literature and in all the examined cases, providing an entry point for integrating the two approaches as both a sector of interest and a mechanism through which compound risks often appear.For example, in the Hindu Kush region, current and projected river variability leads to compound risks in the forms of droughts and floods, while water from the river is a key input to water resource management in the nexus.Water is a common theme throughout all seven cases in the examination of both WEF nexus governance and compound risk in practice.It has been prioritized in nexus governance due to institutional histories of the WEF nexus emerging from the water field [34] and to water's role as a direct input in food production and energy generation.It has been prioritized in compound risk analysis because of the dominance of physical sciences in modeling risks, as water may be more directly tied to climate than food or energy are.While this elevation of water could be an artifact of our case selection, it does provide an important bridge between the two literatures.Previous studies have noted the importance of water resources and water governance as a bridge between other nexus sectors and governance mechanisms [5,34,[53][54][55].This emphasis may be because of differences in infrastructure between water, energy, food, and other resources.Water systems utilize hard infrastructure that are often publicly managed, whereas food infrastructure may rely on more decentralized soft infrastructure and energy infrastructure may be more privatized.Thus, water challenges may provide an entry point to integrate across the two approaches.
Addressing water, energy, and food challenges needs insight from both the WEF nexus and from compound risk to address potential trade-offs and unintended consequences and to create policy and governance approaches that address the complexities within human-environment systems.Despite limited instances of integration between the two approaches in the literature and in example case studies, water systems may serve as an entry point for integration that breaks through silos within the WEF nexus and compound risk to address resource security challenges.Different modalities to build such integration could be explored in future research, to look both for general patterns and place-specific features.For example, a process begun in June 2023 in the Murray-Darling basin in Australia that offers a model of the early stages of such integration.The lead-up to the 2026 review of the basin plan review [56] has led to calls for risk assessment to include fuller consideration of assessment of compound risks [57][58][59] as well as proposals for a series of meetings to increase communication between stakeholders from different sectors, including water, energy and food, as well as, biodiversity, and Indigenous peoples [60][61][62].
Practical integration between the WEF nexus and compound risks could take multiple forms to improve assessment and management outcomes from policymakers and stakeholders; we briefly present three here.First, as suggested by our case studies, we recommend using the water sector as an entry point towards identifying connections between WEF nexus and compound risks in practice, as water concerns related to the WEF nexus and to compound risks were present across all our case studies and could provide an avenue to explore the intersections between these approaches.Second, we recommend that legislation, policy, and planning integrate compound risks for water, energy, and food resource provision by considering existing and anticipated tradeoffs between them.Third, we recommend developing basin-level resilience councils that consider compound risks from climate hazards and include relevant water, energy, and food stakeholders to develop a shared strategy for address nexus-related compound risks.

Conclusions
Silos are still prominent in theory and practice in both WEF nexus governance and compound risk.The literature reviews and the analysis of the case studies both demonstrate these silos.Despite claims in both the nexus and compound risk literatures that these approaches overcome silos, these approaches may in fact be upholding silos by failing to identify related approaches that are important connection points in practice.The failure of WEF nexus governance to consider compound risks between the resourcesand the similar failure of compound risk to consider its impacts on interconnected resource systemsprevents full understanding of interconnected WEF systems and accompanied resource risks.By integrating the two concepts, compound risk can expand understanding of WEF nexus trade-offs and provide a framing for WEF nexus governance in practice, while WEF nexus governance can reveal functioning of specific systems to provide inputs to the assessment of compound risk.Initial efforts in the water sector, such as in the cases of Phoenix and South Africa, offer some hope for progress.Future research should conduct empirical research on the intersection of the WEF nexus and compound risks to understand how the WEF nexus and compound risk might be directly integrated in practice.

Figure 1 .
Figure 1.Frequency of appearance of key terms in the text of summaries for policy-makers in IPCC assessment reports, Working Group III for FAR; Working Group II for all others.

Figure 2 .
Figure 2. Visualization of the conceptual framework, where the WEF nexus is embedded within the larger compound risk system.

Figure 3 .
Figure 3. Map of the seven case studies.Stars represent cases at the sub-national level, filled in countries represent cases at the national level, and rectangles represent studies at the multi-national levels, where the regions generally lie within the box.(Base map source: Esri, FAO, NOAA, USGS [49]).

Table 1 .
A typology of non-simple risks.Type of risk DefinitionCompound Compound risks are risks which interact with each other, so that a change in the level of one risk alters the level of another interconnected risk.