Introduction

The term ‘vulnerability’ has been related or equated to concepts such as resilience, marginality, susceptibility, adaptability, fragility, risk, exposure, sensitivity, coping capacity and criticality (Fuessel and Klein 2006). Although clarification on vulnerability has been repeatedly pointed out as a research need across scientific disciplines (Janssen and Ostrom 2006), the clearest preliminary conclusion reached to date is that there is much confusion (Ionescu et al. 2009).

With vulnerability being a central aspect on a variety of interconnected research fields like food security (Bohle 2001), poverty and livelihoods (Prowse 2003), climate change (Downing et al. 2000) and an extension of traditional risk-hazard analysis (Wisner et al. 2003), a better understanding of the term is deemed fundamental to improve interdisciplinary research on vulnerability (Intergovernmental Panel on Climate Change [IPCC] 2007; Romieu et al. 2010). In addition, the increasing usage of vulnerability assessments as tools supporting policy-making (de la Vega-Leinert et al. 2008) has introduced a new layer of confusion surrounding the term. While scientists make use of the concept of vulnerability to understand the general principles of a system (e.g. its driving forces, state variables) and what can be learned in general from observed situations (Polsky et al. 2007), stakeholders expect vulnerability studies to deliver concrete solutions on how to cope with specific threats (Patt et al. 2005). The challenge of clarifying vulnerability, therefore, goes beyond the discussions between scholars.

Regarding the vulnerability of societies and environments to natural hazards, both risk-hazard and climate-change communities have addressed differences—as well as similarities—of vulnerability at the conceptual level. The approaches ranged from exhaustive collections of definitions regarding vulnerability and related terms (Thywissen 2006), mathematical formalisation of vulnerability concepts (Ionescu et al. 2009) and comparative analysis of several vulnerability models (Hufschmidt 2011). Despite the progress observed, the core source of misunderstanding regarding vulnerability persists, which is that vulnerability is defined by terms that are, themselves, imprecise in meaning (Hinkel 2008). This imprecision leads to vulnerability definitions and frameworks that are mostly useful for setting the scope of vulnerability assessments (Hinkel 2011), while the practical implementation of measuring vulnerability remains deeply tied to specific research, social and environmental contexts (Brooks 2003). In this sense, there is the need to move from the comparison of vulnerability definitions to more detailed descriptions on how vulnerability is measured at the case-study level. The way a researcher interprets vulnerability can be most precisely seen through case studies when vulnerability-measurement methods are described (Wolf et al. 2008). During the elaboration of a case study, the subjective definition of vulnerability and related components acquire a tangible dimension, for example, an indicator, the output of a model or the product of a statistical analysis. Efforts to bridge varying concepts of vulnerability have underlined that only through clear descriptions of vulnerability and vulnerability components can mutual understanding between disciplines and schools of thought be achieved (Fuchs et al. 2011).

In order to move from the subjectivity of semantic definitions, we propose to contrast a set of theoretical formulations of vulnerability components used in climate-change and risk-hazard communities with the corresponding description of measurement methods found at the case-study level.

Scope and material

The work carried out in this paper unfolds in two broad steps. The first step is to construct a theoretical background of commonalities in vulnerability components within and between the communities investigated. We do not intend to make here an in-depth analysis of the use of vulnerability and related concepts across different schools of thought. Instead, we aim at identifying the main similarities and differences between approaches to vulnerability in the risk-hazard and climate-change communities. For this purpose, we have collected commonly used conceptualizations of vulnerability and risk using work by Birkmann (2006), Brooks (2003) and Wisner et al. (2003) as reference. The components used to define vulnerability and risk were then structured according to their positioning in the internal or external sides of vulnerability or risk. Briefly, the external dimension of vulnerability reflects the exposure of a system to shocks from external stressors (Bohle 2001), threats (van Dillen 2004) or climate variation (Fuessel and Klein 2006), while the internal dimension underlies the capacity of the system to anticipate, cope with and recover from an impact (Birkmann 2006). Components were subsequently linked within and between communities in respect to the similarities found. Figure 1 shows an overview diagram of commonalities found between the components used to define vulnerability and risk.

Fig. 1
figure 1

Links of concepts and interpretations between vulnerability and vulnerability components in a risk-hazard and climate-change context (color figure online)

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The second step deals with identifying how vulnerability and vulnerability components are evaluated in the context of a practical assessment. For this purpose, a collection of risk-hazard and climate-change vulnerability studies was gathered. For each case study measuring vulnerability, we have identified: (a) the system that will be the focus of the vulnerability study (e.g. economic sector, geographic space, ecosystem), (b) the perturbation or stress that acts upon (or originates from) the system under analysis, and (c) the main valuated characteristic of the system threatened directly or indirectly by the perturbation or stress (e.g. human lives, biodiversity, economy). The correct description of these criteria is seen as a fundamental starting point in order to avoid confusion on vulnerability (Fuessel 2007). The qualified descriptions of vulnerability for the case studies investigated here can be found in Table 1.

Table 1 Qualified descriptions of vulnerability found in the investigated case studies in a risk-hazard (a) and climate change (b) context. The valued characteristic of the assessment, the perturbation or stress acting upon the system of interest and the system itself are shown (see also the text in the Scope and material section)
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From the methodological description of vulnerability, we have identified the indicators and analysis used in the quantitative/qualitative estimates of vulnerability and risk components. This allows us to assess how far the employed methodologies are from the theoretical definitions of vulnerability (Hinkel 2008), thus, revealing a clearer understanding of the vulnerability components by the author. As an example, we proceed with a description of the work undertaken for one case study.

Menoni et al. (2002) assessed the systemic vulnerability of lifelines to earthquakes in Regione Lombardia, Italy. The methodology was applied to three spatial regions in Regione Lombardia that are said to be homogeneous in regard to their geographic and urban features. The aim of the assessment was to evaluate the lifeline (e.g. water and energy systems) performance—measured as damage or failure—in the eventuality of an earthquake. Vulnerability scores are derived by weighting multiple indicators that address current functional, organisational and physical characteristics of lifelines (e.g. power systems). Vulnerability scores are obtained for the emergency, recovery and reconstruction phases. In Menoni et al. (2002), the magnitude of a possible earthquake is not considered in assessing the final vulnerability score. Vulnerability as interpreted by Menoni et al. (2002) is independent of the magnitude of the perturbation (earthquake) and restricted to the present functional, organisational and physical characteristics of lifelines in Regione Lombardia. A similar procedure was made for the complete collection of case studies. The commonalities between vulnerability components as described in the investigated case studies are shown in Fig. 2.

Fig. 2
figure 2

Links between vulnerability components as described in the methodology of the investigated case studies (color figure online)

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Vulnerability and risk concepts investigated

Risk-hazard context

The investigated definitions of vulnerability in the risk-hazard and climate-change contexts are shown in Fig. 1. In a risk-hazard perspective, the conceptualisations of vulnerability were gathered in order to reflect different dimensions of vulnerability, such as built environment or social and human ecology (top left side of Fig. 1).

Vulnerability focusing on the built environment was found to be defined by components such as ‘intensity’ and ‘susceptibility’. Intensity represents the external side of vulnerability and is defined as the impact on an element at risk (Totschnig et al. 2011). Susceptibility is said to be the inherent capacity of the elements to preserve their physical integrity and functionality (Kaynia et al. 2008) and it characterises the internal side of vulnerability.

When the focus of vulnerability is the social system, vulnerability highlights mainly the socio-cultural and economic processes that determine the ability of societies and individuals to cope with and respond to disasters (Cutter 1996). The prominent example of Watts and Bohle (1993) and Bohle (2001) defines vulnerability as the interaction between the components ‘exposure’ and ‘coping capacity’. Exposure denotes the external side of vulnerability and refers to shocks and stresses that individuals or households are subjected to. The internal dimension, coping capacity, is defined as the manner in which people access and control assets of different nature, manage crisis situations or act as a result of societal or economic constraints (Bohle 2001).

Contrary to the technical view on vulnerability, the evaluation of social vulnerability directs its efforts to the underlying factors reducing the capacity of the human system to cope with a range of hazards, rather than the negative impacts following the occurrence of a hazard. Exposure seems, therefore, to originate from the social system itself, rather than being external to the system. In a social context, exposure is influenced by population dynamics, capacities to manage the environment, the incapacity to obtain assets via legitimate economic means and social inequalities (Villagrán de León 2006).

When the focus of vulnerability is broadened to a human-ecology perspective, it is usually defined by the interaction between the elements exposure, susceptibility and coping capacity. In Fig. 1, we depict the formulation of vulnerability according to White et al. (2005) and Scheuer et al. (2011). Exposure is placed on the external side of vulnerability and is described as the frequency and severity of weather-related disasters (Scheuer et al. 2011). On the internal side, susceptibility is said to be the social, economic, political, psychological and environmental variables that intervene in producing different impacts amongst people with similar levels of exposure. Finally, coping capacity represents the attributes of livelihoods or economic systems which enable losses to be absorbed (White et al. 2005).

In a risk-hazard context, vulnerability is also used as a component defining risk (bottom left side of Fig. 1). In this case, vulnerability moves to the internal side of risk—either alone or in combination with components such as exposure or capacity measures. For example, the United Nations Development Programme (UNDP) defines risk as the product between ‘hazard’ and ‘vulnerability’. Hazard is a potentially damaging physical event, phenomenon or human activity, while vulnerability is the physical, social, economic and environmental factors or processes which increase the susceptibility of a community to the impact of hazards (UNDP 2004). The risk triangle conceptualisation by Crichton (1999) adds the component exposure to the internal side of risk, vaguely defined as people and assets exposed to hazards. Other variations of the risk concept include components like capacity measures (Davidson 1997) or deficiencies in preparedness (Villagrán de León 2001). In all risk frameworks considered, hazard represents the external side of risk and was broadly defined as a function of probability, predictability, extent and intensity of the impact (Alwang et al. 2001).

Climate and global-change context

In a climate and global-change perspective (right side of Fig. 1), two conceptualisations of vulnerability have emerged as prominent: Turner et al. (2003) and the one in use by the IPCC. Both conceptualisations frame vulnerability as a function of ‘exposure’ and ‘sensitivity’. The main difference lies in the formulation of a third component, ‘resilience’ in the case of Turner et al. (2003) and ‘adaptive capacity’ in the case of the IPCC (2007).

Resilience is defined as the ability of a system to bounce back to a reference state after a disturbance and also as the capacity of a system to maintain certain structures and functions (Turner et al. 2003). The IPCC (2007) defines adaptive capacity as the ability of a system to adjust to climate change by moderating the potential damages, take advantage of opportunities and cope with the consequences.

Exposure is a common element defining vulnerability in the IPCC (2007) and Turner et al. (2003) frameworks. Also common is the vagueness of its definition. For example, the IPCC (2007) defines exposure as the nature and degree to which a system is exposed to significant climatic variations. Turner et al. (2003) proceed in a similar way, framing exposure as the interaction between system components and stressor characteristics. This is a classic example of where a definition calls for further clarification. What the authors understand by nature, degree or interaction remains unclear.

Linking definitions of vulnerability and risk components

Exposure, hazard and intensity

In a risk-hazard context, the term exposure was found to be represent both the internal side of risk and the external side of vulnerability. Exposure as a component of vulnerability addresses not only the extent to which a system is subjected to perturbation, but also the degree and duration of that perturbation (Adger 2006). When exposure is a component of risk, it addresses the inventory of people and artefacts exposed to a hazard (UNDP 2004; Crichton 1999). In his risk framework, Villagrán de León (2001) avoids using explicitly the term exposure, subsuming it under the definition of vulnerability (Birkmann 2006). No strong links between exposure as a component of risk and exposure as a component of vulnerability are, therefore, established. There seems to be, nevertheless, a link between exposure and intensity (components of vulnerability in human environment and technical dimensions) and hazard as a component of risk (see Link#1 in Fig. 1). The intensity, probability and locational aspects defining hazard (as in the UNDP 2004) can be subsumed under the definition of exposure in White et al. (2005), that is, the frequency and severity of disasters. Similarly, Totschnig et al. (2011) explicitly use the component ‘intensity’ to classify the size of hazard. It is apparent that Link#1 could be broadened to exposure as a component of vulnerability in global and climate change research. Because the term exposure is not conveniently defined by Turner et al. (2003) or the IPCC (2007), we have avoided establishing any connection at this point.

Sensitivity, susceptibility and vulnerability

As seen before, the component sensitivity is common in the climate and global-change descriptions of vulnerability. The term appears to be linked, to some extent, with susceptibility as defined by White et al. (2005) (see Link#2 in Fig. 1). Susceptibility is defined as the socio-economic and physical characteristics of a system that differentiate the magnitude of impacts for a given exposure. In Turner et al. (2003), sensitivity is said to be determined by the human environment conditions of the system subjected to any set of exposures.

The IPCC (2007) defines sensitivity in a broader sense without mentioning its determinants. Sensitivity is the degree to which a system is affected by climate variability or change. This definition is close to the interpretation of vulnerability as a component of risk, that is, the degree of loss resulting from the occurrence of a natural phenomenon of a given magnitude (United Nations Educational, Scientific and Cultural Organization [UNESCO] 1986). A link between the component sensitivity in the IPCC terminology and the component vulnerability as a component of risk is, therefore, established (see Link#3 in Fig. 1).

Adaptation, coping capacity and resilience

The IPCC (2007) definition of adaptive capacity, that is, the ability of a system to adjust to climate change to moderate potential damages, to take advantage of opportunities or to cope with the consequences, appears to include the idea of deficiencies in preparedness and coping capacity (see Link#4 and Link#5, respectively, in Fig. 1). Although different in terminology, all terms do refer to the ability of a system to cope with the hazard stress (Taubenböck 2008; Birkmann 2006). The term adaptive capacity underlines the ability of a system to change, while coping capacity refers to the ability to absorb impacts by guarding against or adapting to them (UNEP 2002). The term resilience appears to be the most encompassing of all (Thywissen 2006), including both the notions of coping capacity found in the risk-hazards frameworks and adaptive capacity found in the IPCC (2007) formulation of vulnerability (see Link#6 in Fig. 1).

Linking components of vulnerability as described in the methodology of case studies

Structured descriptions of vulnerability derived from the case studies investigated here are presented in Table 1. Information of what/who is vulnerable to what stress/perturbation in a given system/region is presented in a systematic way. Our case study selection—although not exhaustive—does include example of vulnerability assessments for a variety of damaging events (e.g. floods, earthquakes, landslides, climate change and variability), covering different foci (e.g. structures, economy, society and ecosystems) and unfolding at several spatial scales (e.g. local, regional and continental). In Fig. 2, the methodological description of vulnerability components found in the case-study analysis and highlighted in Fig. 1 are shown.

At the practical level of a vulnerability assessment, the links between vulnerability and risk components established in the theoretical analysis have been broadly recognised. The commonalities at the practical level appear to be even stronger than those observed from the semantic definitions of the components of vulnerability. For example, in order to evaluate hazard and exposure (see top of Fig. 2), both investigated communities relied on the use of future scenarios. This was observed across several spatial scales and vulnerability foci. Rashed and Weeks (2003) interpreted hazard as a set of earthquake intensities and Schröter et al. (2005) state that the exposure side of vulnerability is represented by different levels of climate change. In Table 1, earthquake and climate change are said to be the main perturbation/stress in Rashed and Weeks (2003) and Schröter et al. (2005), respectively. At a more detailed spatial scale, Granger (2003) interpreted hazard as a set of annual exceedence probabilities of storm tides. Independent of the focus (structures, urban areas, ecosystem services), the system of concern (town of Cairns, LA county, Europe; see Table 1) or the vulnerability/risk conceptualisation used, exposure and hazard were interpreted in both communities as likely degrees of pressure acting upon a system.

Susceptibility, sensitivity and vulnerability appear to share the largest number of commonalities during the elaboration of investigated assessments on vulnerability (see blue boxes in Fig. 2). A new link between susceptibility and vulnerability emerged with the correspondent descriptions of employed methodologies. When the focus of vulnerability was placed on society, both climate-change and risk-hazard studies evaluated the respective components of vulnerability with reference to very similar collections of socio-economic indicators. For example, Fekete et al. (2010) make use of the indicators age, living space per person, education and population density to determine susceptibility at the county level in Germany. In a climate-change context, Brenkert and Malone (2005) and Hahn et al. (2009) evaluate sensitivity via an analogous procedure.

The components sensitivity in climate change and vulnerability in risk-hazard contexts were, in some cases, interpreted in a similar way, even when the valued characteristic of the vulnerability assessment, the systems and the perturbation or stress are remarkably different (see Table 1 for details). For example, Schröter et al. (2005) interpret sensitivity as being included in the response of biophysical models to exposure; this is close to vulnerability expressed by the relation between damage ratio and process intensity—as described in Totschnig et al. (2011).

The analysis of case studies also revealed differences in the interpretations of vulnerability components within the same community. For example, the understanding of sensitivity of the Indian agricultural sector to climate change in O’Brien et al. (2004) seems at odds with what has been observed in other case studies (see sensitivity as described in Hahn et al. (2009) in Fig. 2). The sensitivity component was interpreted as a combination of climatic variables such as a dryness index and average occurrence of extreme rainfall. This interpretation is much closer to exposure as defined in climate change—the degree to which a system is affected by climate variability or change (IPCC 2007). When the threat to the Indian agricultural sector is globalisation, then sensitivity in O’Brien et al. (2004) is in line with sensitivity as interpreted by Brenkert and Malone (2005) and even the component susceptibility as in Fekete et al. (2010). Broadly speaking, it is the socio-economic and environmental characteristics of a system that shape the degree of impacts.

The relation between the components vulnerability and susceptibility in assessments carried out in a risk-hazard context was found to be particularly interesting. Case studies focusing on the vulnerability of people and structures have determined sensitivity via assessing the typology and maintenance characteristics of structures and socio-economic aspects of the population in the study area, as described in Kaynia et al. (2008). The aspects of structure typology and structure maintenance can be related, to some extent, to the vulnerability understanding in Menoni et al. (2002), that is, the structural, organisational and functional characteristics of lifelines. Similarly, the societal dimension of vulnerability was evaluated using socio-economic indicators of the study area (e.g. education, age, population density), as in Kaynia et al. (2008) and Fekete et al. (2010). When vulnerability was operated as a component of risk (see Granger (2003) in Fig. 2), and the focus of the assessment is on society, it referred to a set of socio-economic indicators of the study area (e.g. people over the age of 65 years, road network density). This is in line with previously highlighted operations of susceptibility and sensitivity in risk-hazard and climate-change studies, respectively.

Finally, when assessing the vulnerability of society, the components adaptation, capacities, susceptibility and, to some extent, sensitivity were estimated in remarkably identical ways. Indicators such as per capita gross domestic product (GDP) or household income were used simultaneously to derive the vulnerability components capacities and adaptation (see bottom of Fig. 2).

Discussion

For each definition of vulnerability within the risk-hazard community, there seems to be an equivalent (or with a similar meaning) in global and climate-change context. Despite the limited number of case studies investigated here, the results do point to a lower level of heterogeneity in vulnerability interpretations at the case-study level.

It was observed that multiple interpretations of vulnerability components found in theoretical frameworks do not necessary translate into distinct approaches or methodologies in assessing vulnerability in risk-hazard and climate-change contexts. This evidence was particularly strong during the evaluation of the vulnerability of societies. In the cases analysed here, sensitivity, susceptibility and vulnerability (when defined under risk) seem to be interchangeable in meaning.

The commonalities between both communities found at the practical level also supports the suggestion that, in order to respond rapidly to evolving policy demand, vulnerability has been equated with a narrow set of mainly biophysical or economic parameters and recurring to pre-existing modelling frameworks (Nelson et al. 2010). Much confusion in discussing vulnerability seems to result from the process of adapting existing impact methodologies to accommodate the evolving and widening concept of vulnerability (Fuessel and Klein 2006; Birkmann 2006).

The long persistence of confusion surrounding vulnerability and related concepts calls for a greater emphasis in systematically assessing how vulnerability components are made operational at the case-study level. The approach here outlined is a way to disentangle the meaning of the word ‘vulnerability’ across scientific communities and also a contribution for improving the communication of vulnerability in a decision-making context.