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Climate Variability and Change in Mobile, Alabama

1. Introduction and Background

1.1. Overview of Gulf Coast Project

Despite increasing confidence in global climate change projections in recent years, projections of climate effects at local scales remains scarce. Location-specific risks to transportation systems imposed by changes in climate are not yet well known. However, consideration of these long-term factors are highly relevant for infrastructure components, such as rail lines, highways, bridges, and ports, that are expected to provide service for up to 100 years.

To better understand climate change impacts on transportation infrastructure and to identify potential adaptation strategies, the U.S. Department of Transportation's Center for Climate Change and Environmental Forecasting is conducting a comprehensive, multiphase study of climate change impacts on transportation in the Central Gulf Coast region. This study, formally known as Impacts of Climate Change and Variability on Transportation Systems and Infrastructure: Gulf Coast Study (hereafter, "the Gulf Coast Study"), is the first such study of its magnitude in the United States and represents an important benchmark in the understanding of what constitutes an effective transportation system adaptation planning effort.

The Gulf Coast Study was initiated to better understand climate change impacts on transportation infrastructure and to identify potential adaptation strategies. The Gulf Coast region was selected as the focal point due to its dense population and complex network of transportation infrastructure, as well as its critical economic role in the import and export of oil, gas, and other goods. The study is funded by the USDOT Center for Climate Change and Environmental Forecasting and managed by FHWA. The U.S. Geological Survey (USGS) has provided support for much of the climate science work. The Gulf Coast Study includes two phases:

Phase 2 Study Area

While Phase 1 took a broad look at the entire Central Gulf Coast region (between Houston/Galveston, Texas and Mobile, Alabama) with a 'big picture' view of the climate-related challenges facing infrastructure, the current effort in Phase 2 focuses on Mobile, Alabama. The area of the study includes Mobile County (including Dauphin Island) and the crossings of Mobile Bay to the east to landfall in Baldwin County (Figure 2).

Phase 2 includes the following tasks:

figure 2: Study Area

This figure shows a map of the study area for the Gulf Coast study. The study area includes Mobile county (including Dauphin Island, a barrier island in the Gulf of Mexico south of Mobile); and a portion of western Baldwin county that contains the crossing of Mobile Bay.

1.1.1. Gulf Coast, Phase 1: Results

In the first phase, USDOT had four main objectives: (1) to gather data critical for analyzing the impacts of climate change on transportation infrastructure; (2) to determine whether climate data could be valuable in assessing vulnerability of infrastructure in the region; (3) to identify and implement an assessment approach; and (4) to then develop an overview of the potential impacts on infrastructure. The Phase 1 study utilized historical data on weather events, recent climate data, and projected changes in climate for the coming century.

Phase 1 study results indicate that the Gulf Coast region is particularly susceptible to climate change over the 21st century. Some of the changes projected for the region include the following:2

The implications of projected changes in climate for regional transportation systems are significant. Increasing temperatures are likely to require modifications to system materials, maintenance, and operations. Increased severity of precipitation events could cause more flooding, threatening the stability of soils and foundational materials, stressing the capacity of drainage systems, and disrupting operations. The combined effects of land subsidence and absolute sea level rise (SLR) could permanently inundate existing infrastructure, including 27% of major roads, 9% of rail lines, and 72% of ports (depending on sea level rise scenarios, and excluding protective structures). Finally, an increase in severity of tropical storms could have significant impacts on coastal infrastructure. Damages due to storm surge, winds and flying debris can be catastrophic, disrupting service and causing costly damage to infrastructure.

1.1.2. Gulf Coast, Phase 2: Overview of Tasks

While Phase 1 took a broad look at the entire Central Gulf Coast region (between Galveston, TX and Mobile, AL) with a 'big picture' view of the climate-related challenges facing infrastructure, Phase 2 is focusing on a single Metropolitan Planning Organization (MPO) region around Mobile, Alabama.

The purpose of this phase is to evaluate which transportation infrastructure components are most critical to economic and societal function, and assess the vulnerability of these components to weather events and long-term changes in climate. Phase 2 will also develop tools and approaches that the Mobile MPO and other public and private system operators can use to determine which systems need to be protected, and how best to protect them. Through this study, USDOT intends to create a process that can be replicated in other MPO regions.

Phase 2 is divided into the tasks below. The first three tasks form the basis of a vulnerability screen and assessment of the Mobile transportation system, while the other tasks focus on tool development, coordination with stakeholders, and communication of project results.

1.2. Overview of Task 2

This report, the Task 2 report, lays the climate data foundation upon which a vulnerability assessment will be conducted in the next task. In future steps of the project, a vulnerability screen will be conducted along with an assessment of the highly critical assets identified previously under Task 1, as reported in the Task 1 final report Assessing Infrastructure for Criticality in Mobile, AL.3

This report explores potential changes in five primary climate variables: temperature, precipitation, streamflow, sea level rise, and storm surge in Mobile, Alabama, the location selected as the study area for Phase 2. To do so, Task 2 characterizes the current climate conditions in Mobile, and then uses downscaled climate projection data, as well as sea level rise and storm surge modeling, to develop plausible climate futures. The climate information discussed in this report will be used to assess how the transportation system in Mobile might be affected by climate change.

Although this report does focus on Mobile, Alabama, the processes developed under this Task can be replicated by other transportation organizations across the country. The ultimate goal of this report is to not just identify how climate could change in Mobile, but also to develop robust methodologies, and identify existing datasets and tools, for developing these plausible climate futures. Furthermore, the work conducted under Task 2 will help inform the development of tools and resources to make these types of analyses easier for transportation agencies. To that end, the methodology of Task 2 is equally important as the results. Section 8 provides a discussion of how the lessons learned and information developed under Task 2 will be used in other products for different audiences.

Figure 3 below illustrates the components of this report and how they fit within the overall Gulf Coast Phase 2 project.

Figure 3: Roadmap for Phase 2 of the Gulf Coast Project

This figure shows a flow chart explaining how Task 2 fits in to the overall Gulf Coast study. Task 2, the development of climate information, involved understanding how climate may change in Mobile, AL. Task 2 also contains a sensitivity matrix and screen, which is not a part of this report. Findings from Task 2 will feed into the Task 3 vulnerability assessment of Mobile’s transportation system, particularly the assessment of exposure and sensitivity. Tasks 1 through 3 will feed into Task 4, the development of tools and resources based on lessons learned from the study.

Note: The components covered by this report are indicated with blue shading. The gray shading indicates other components of the Phase 2 study that are covered under other tasks and reports.

1.3. Report Roadmap

The main body of this report is organized by climate variable, with one section dedicated to each of the following variables:

Within each of those sections, this report first characterizes the current climate in Mobile, AL, and then discusses potential climate futures. As noted previously, the approach is considered just as important as the results, to help serve as a resource for other agencies planning similar assessments. Therefore, both the methodology used and the results of the analyses are presented. Detailed information on the methodology and results are presented in the report Appendices. In addition to the key findings of the analysis, each section includes a discussion on the implications of the potential climate futures for the transportation sector.

The final section of this report includes a discussion of how the information developed in this report will be used for later activities under this project, and how it will inform the work of activities beyond this project.


1 Available at: http://www.fhwa.dot.gov/environment/environment/climate_change/adaptation/ongoing_and_current_research/gulf_coast_study/

2 USCCSP 2008a.

3 Available at http://www.fhwa.dot.gov/environment/climate_change/adaptation/ongoing_and_current_research/gulf_coast_study/.

Updated: 10/31/2014
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