In this report, the term "asset" refers to both physical transportation assets, such as roads and bridges, as well as services, such as maintenance and driver safety.
One of the most important questions currently facing transportation officials is how to efficiently invest in and design improvements to transportation systems in order to reduce vulnerability to climate variability and change. Sensitivity, the degree to which an asset or a system responds to a given change in climate impact, is a key part of evaluating vulnerability and risk. Since sensitive assets will experience higher levels of damage when subjected to relatively small climate variations as compared to their non-sensitive counterparts, understanding the relative sensitivity of various assets can help transportation officials make targeted system improvements to reduce vulnerability.
The purpose of this report is to review transportation assets in Mobile, Alabama and to qualitatively assess their sensitivity to changes in climate. Two products were created to address these objectives: (i) a Sensitivity Matrix that identifies relationships, thresholds, and indicators of sensitivity for transportation assets, and (ii) a Sensitivity Screen that planners and decision makers can use to quickly assess whether transportation assets are sensitive to certain climate stressors. This final report describes these two products, presents the methodology for their development, and provides key conclusions derived from them.
The intended audience for the Sensitivity Matrix and Screen includes local and regional planners who are attempting to prioritize and focus climate risk analyses on the most sensitive assets under their purview. Planners can use the Sensitivity Screen to identify assets that are sensitive to a particular climate impact as part of a high-level screening process to determine areas of vulnerability within a system. The Sensitivity Matrix provides a deeper level of detail including information on the threshold at which assets become sensitive, historical precedents for climate-related damage to that asset type, and features of the asset which may be associated with increased sensitivity. Planners can use the Sensitivity Matrix as one piece of a more detailed climate vulnerability and risk assessment. While the specific results presented in this report are specific to Mobile and the Gulf Coast region, the methodologies, screens, and assessment techniques presented here are transferable to other regions.
Concurrently with this effort, the Gulf Coast Phase 2 project developed climate projections for Mobile. It is important to note that those climate projections will be used in conjunction with the sensitivity information contained in this report under Task 3 to conduct a vulnerability assessment of Mobile's transportation system. As such, the results presented in this report consider overall sensitivities of transportation assets and operations, but do not evaluate the vulnerability of those assets and operations to the specific climate projections developed for this project. Such an assessment will occur in the next project task.
Key Terms and Concepts
The Intergovernmental Panel on Climate Change (IPCC) describes the vulnerability of a system to climate change as a function of the character, magnitude, and rate of climate variation to which a system is exposed, the sensitivity of the system, and its adaptive capacity. This relationship is mathematically represented by the equation:
Vulnerability = f(Exposure, Sensitivity, Adaptive Capacity)
Sensitivity: The change in the condition of an asset given a change in a particular climate stressor.
Exposure: The extent to which a system is subjected to a particular climate stressor.
Adaptive capacity*: The ability of a system to adjust to climate change (including climate variability and extremes) to moderate potential damages, to take advantage of opportunities, or to cope with the consequences.
Climate variable: Parameters used to measure and describe climate. For the purposes of this report, six different climate variables were examined: temperature, precipitation, wind, storm surge, waves, and relative sea level change.
Climate stressor: Variation in a climate variable that may lead to a climate impact (e.g., high temperatures, heavy rainfall, cyclical variations in temperature over a period of time).
Climate impact: The effect that climate has on a transportation asset.
* "Resilience" is sometimes used interchangeably with the term "adaptive capacity;" but is also used in the adaptation literature as a term related to, but distinct from, adaptive capacity; and sometimes as a concept representing the opposite of vulnerability. To avoid the confusion associated with the term "resilience," this study exclusively uses the term "adaptive capacity."
The Sensitivity Matrix and the Sensitivity Screen developed during this project are housed together in a single spreadsheet workbook.1 The Matrix documents the sensitivities of 28 transportation sub-modes to the following four major climate variables and associated stressors. The Matrix focuses on these particular stressors since research indicated that they are the most relevant to transportation assets in the Gulf Coast region.
Multiple similar types of climate changes (e.g., waves, storm surge, and long-term sea-level rise) were aggregated into each category because the effects of these factors tend to be similar though not always identical. By reducing the number of categories, the size of the large Matrix is minimized. Another reason for grouping different types of climate changes is that empirical information on effects of the various sub-categories may be lacking. For example, there is much more empirical information on the sensitivity of transportation infrastructure to short-term flood-related impacts than long-term sea-level rise. The sensitivities specified in the Matrix are specific to each sub-category of climate change, where appropriate, and generalized where possible.
The Approaches for Characterizing Sensitivity section of this report discusses the definition of sensitivity and different approaches for characterizing it using an example from the Sensitivity Matrix. The Methodology section details the six step process that was used to develop the Sensitivity Matrix, the main information sources that were used, and the development of the Sensitivity Screen. The Results section of the report presents the major conclusions that can be drawn from the overall sensitivity assessment. Finally, the Next Steps section describes next steps for the Gulf Coast Phase 2 project and also explains how the Sensitivity Matrix and Screen can be used by transportation planners in regions outside of the Gulf Coast.