Vulnerability: Information and Examples

Climate Change Vulnerability Assessment (CCVA) Background

CCVA Introduction

The IPCC defines vulnerability as “the degree to which a system is susceptible to, or unable to cope with, adverse effects of climate change” (IPCC 2007). CCVAs are unique instances of more general impact assessments (Rowland et al. 2011; hi). Species CCVAs can also roughly be considered a sub-type of Population Viability Analysis (PVA). CCVAs do not explicitly define “vulnerability”, nor (generally) quantify extinction risk; instead CCVAs qualitatively assume that more vulnerable species are at greater risk of decline. Although we use the term “species” CCVA for simplicity, CCVA can also be equally applied to taxon, sub-populations, or ecosystems.

What, exactly, differentiates a CCVA from other impact assessments or viability analyses?  

1. CCVAs seek to identify the causes of potential impacts so as to suggest conservation and mitigation actions (Füssel & Klein 2006).

2. CCVAs  should account for the three components of vulnerability (IPCC 2007): exposure (the magnitude or risk of physical changes in climate conditions); sensitivity (the likelihood of adverse effects to an organism or system given climate changes; can be considered akin to dose-response);  and adaptive capacity (the intrinsic ability for an organism or system to reduce its sensitivity by successful response to changing climate [e.g., adaptive responses or range shifts]).  

3. CCVAs rely on projections of potential future conditions, primarily climatic, although future projections of other stressors can also be included.  

4.  Vulnerability is a theoretical concept and, therefore, cannot be directly measured or statistically scrutinized. As a result, vulnerability must be assessed using indicators as proxy measures of its various components.

5. CCVAs generally provide relative, comparative rankings of vulnerability as opposed to nominal values. Although certain vulnerability proxy measures may have known empirical relationships (e.g., temperature thresholds that increase mortality rates or habitat areas that reduce population size), a CCVA is generally conducted to guide management when empirical relationships are not known for the majority of stressors thought to increase vulnerability .  When mechanistic or statistical models are applied to link stressors to quantify species extinction risk, these analyses blur into population viability assessments.

Beyond the five characteristics listed above, overly proscriptive CCVA methods are likely not useful. Each species CCVA will have differing goals and methods should be tailored to the purpose (Hinkel 2011).


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CCVA’s Role in Salmonid Conservation Science

Climate Change Vulnerability Assessments (CCVA) do not incorporate the full circle of the scientific method. Instead, CCVAs represent hypotheses, not predictions, about how species will respond to climatic perturbations. A single CCVA should not be used as the sole method for identifying where to apply scarce conservation dollars. CCVA are one step in a larger conservation planning process that requires consideration of other lines of evidence, multiple scenarios, and on-going monitoring of species’ responses to climatic change over time.


CCVAs should be seen as complementary analyses to other conservation modeling tools, such as population viability assessments, range shift modeling, and other finer-scale empirically and statistically based models. For example, viable salmon population (VSP) guidelines used by the National Oceanic and Atmospheric Administration (NOAA) for determining the conservation status of Pacific salmonids consider measures of salmonid population abundance, growth rate, spatial structure, and diversity (McElhany et al. 2000). These same measures would be natural proxies for assessing a population’s sensitivity or adaptive capacity in a CCVA framework. Other viability assessment models and tools can provide in depth modeling of individual components of CCVA proxy metric or test qualitative hypothesized relationships in a more quantitative framework.


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Toward More Robust CCVAs

The purpose of a Climate Change Vulnerability Assessment (CCVA) is to assist managers in planning and prioritizing conservation actions which, ultimately, require tradeoffs between species or locations. Failure to maximize the scientific rigor and robustness of CCVA may lead to inappropriate allocation of resources, missed opportunities, or worse. Here, we suggest improvements to increase CCVA robustness and reliability.

    1.        Improve Comparability – The scientific process requires replicability of results. Making CCVAs more directly comparable echoes this need. Currently, the term “climate vulnerability assessment” is applied widely across systems (e.g., biological, social, social-ecological), applications (e.g., aspatial rankings vs. spatially-explicit approaches), methods (e.g., variable inclusion of exposure, sensitivity, and adaptive capacity metrics and how those are defined and quantified). Currently lacking a classification scheme, making the title of a CCVA more descriptive would be a first step, along with a visual depiction of the methods to help readers quickly identify the general methodological framework applied.

    2.        Conceptual Models to Describe and Improve Hypotheses -  Conceptual models provide a structured expression of the a priori hypotheses about system function, allowing formal testing about how components and processes are related even when knowledge of the system is sparse (Manley et al. 2004), as is often the case for CCVA. In addition to providing a visual depiction of methods and assumptions, conceptual models are an excellent means to fold CCVA into the broader scientific process of hypothesis testing as new data and information become available.

    3.        CCVA as a Complementary Approach to Other Conservation Science Models – CCVAs should not be considered in a vacuum. Other models can be used to test linkages within the conceptual model. CCVA results can be compared to other approaches, such as the Viable Salmon Population (VSP) approach of NOAA. Alternative approaches, such as Bayesian Networks, Population Viability Modeling, Ecological Niche Modelling, and Landscape Genetics can all be used for both integration into a CCVA and comparison across modeling approaches (see point 5, below).

    4.        Remember Adaptive Capacity – There are challenges associated with precisely defining adaptive capacity, and the concept is often muddled with sensitivity. In some instances, categorization of whether a metric is sensitivity or adaptive capacity may be semantics. Ultimately, adaptive capacity acts to reduce species sensitivity, and as such the two are linked theoretically in CCVA but also directly in nature (i.e., eco-evolutionary dynamics; Schoener 2011). Essentially, demographic, phenotypic, genetic and environmental variation all interact with one another to influence eco-evolutionary dynamics, and dictate climate change vulnerability.  Although we may not be able to directly predict how climate-induced selection may act on certain genes, we are able to measure a variety of biological and environmental variables that operate directly at the sensitivity/adaptive capacity interface.

    5.        Quantify Uncertainty and Test for Robustness – Many CCVA guidelines urge uncertainty analysis, but few CCVA do this in practice. A given CCVA is one hypothesis about how a system works; different methods will predetermine different results. Uncertainty across all levels of data (climate models, climate scenarios, hydrological models, land use, life history models, etc.) also affect results. Making CCVA more robust requires integration of multiple lines of evidence and continued research to fill in knowledge gaps.  At a minimum, CCVAs, whether aspatial rankings or spatially-explicit maps, should include sensitivity testing of results dependent on chosen proxy metrics. Importantly, monitoring is ultimately required to empirically validate and refine hypothesized relationships within the CCVA (via the conceptual model).


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Introduction References

Dawson, T. P., S. T. Jackson, J. I. House, I. C. Prentice, and G. M. Mace. 2011. Beyond Predictions: Biodiversity Conservation in a Changing Climate. Science 332:53–58.

Füssel, H.-M., and R. Klein. 2006. Climate change vulnerability assessments: an evolution of conceptual thinking. Climatic Change 75:301–329.

Hinkel, J. 2011. “Indicators of vulnerability and adaptive capacity”: Towards a clarification of the science–policy interface. Global Environmental Change 21:198–208.

IPCC (International Panel on Climate Change). 2007. Climate Change 2007: Synthesis Report. Contribution of Working Groups 1, II, and II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change 1. IPCC, Geneva, Switzerland.

Manley, P. N., W. J. Zielinski, M. D. Schlesinger, and S. R. Mori. 2004. Evaluation of a multiple-species approach to monitoring species at the ecoregional scale. Ecological Applications 14:296–310.

McElhany, P., M. H. Ruckelshaus, M. J. Ford, T. C. Wainwright, and E. P. Bjorkstedt. 2000. Viable salmonid populations and the recovery of evolutionarily significant units. Page 156. NMFS-NWFSC-42. National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, WA.

Rowland, E., J. Davison, and L. Graumlich. 2011. Approaches to evaluating climate change impacts on species: a guide to initiating the adaptation planning process. Environmental Management 47:322–337.

Schoener, T. W. 2011. The Newest Synthesis: Understanding the Interplay of Evolutionary and Ecological Dynamics. Science 331:426–429.


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CCVA Examples


Steelhead and Bull Trout Multispecies CCVA in the Columbia River Basin

Climate change will compound existing stresses to numerous species. Salmonids, which are economic and ecological mainstays of the Pacific Northwest, are a case in point. Salmonids, with several populations already listed as threatened under the ESA, are adapted to cold water and current hydrological regimes, both of which are projected to shift under a changing climate. Vulnerability assessments are useful to understand the spatial patterns of projected climate impacts. However, previous vulnerability studies consider climate and habitat factors, but fail to include genetic and demographic components critical to species viability. Here we take a multispecies approach to vulnerability, assessing potential climate threats to two salmonids with different life histories – steelhead and bull trout. We include both genetic and demographic measures of vulnerability to assess how climate impacts may vary across space and species.

a) Bull Trout

b) Steelhead

Conceptual models for a) Bull trout and b) Steelhead. the conceptual models include factors and stressors influencing each species vulnerability to climate change.

a) Bull Trout

b) Steelhead

Projected bull trout a) and steelhead b) vulnerability to climate change (2040s scenario, RCP 4.5) in the Columbia basin.



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Steelhead CCVA in the Pacific Northwest

In this manuscript, a spatially explicit method for assessing salmon vulnerability to projected climatic changes is demonstrated. The assessment does not include adaptive capacity, but includes exposure to both stream temperatures and flows across four of steelhead’s primary freshwater life stages: adult migration, spawning, incubation and rearing. Steelhead sensitivity to climate change was estimated on the basis of their regulatory status and the condition of their habitat.






Projected steelhead exposure to scenarios of changes in stream temperature (a) and flow (b) and estimated sensitivity of steelhead on the basis of habitat condition (c) and population status (d). Results for ac are categorized by Pacific Northwest-wide relative quintile. White triangles show locations of large dams known to block upstream steelhead migration.


Wade, A. A., T. J. Beechie, E. Fleishman, N. J. Mantua, H. Wu, J. S. Kimball, D. M. Stoms, and J. A. Stanford. 2013. Steelhead vulnerability to climate change in the Pacific Northwest. Journal of Applied Ecology 50:1093–1104.


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Salmon Stress Index

North Pacific Rim basins were ranked according to regional patterns of environmental stress for salmon under current and projected future (to 2100) climate conditions. The basin rankings account for the relative abundance and distribution of freshwater habitats in each basin and include dynamic river flow and temperature simulations as indicators of water quality. A salmon stress index was developed based on temperature thresholds for spawning, incubation, and rearing for individual salmon species. The salmon stress ranking was coupled with the sub-watershed physical complexity ranking to develop a watershed vulnerability index for individual salmon species.

Click Here to View Maps for Chinook or Coho


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