Extreme weather events currently disrupt transportation networks in all areas of the country; projections indicate that such disruptions will increase.

This finding is from chapter 5 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: In developing key messages, the chapter author team engaged, via teleconference, in multiple technical discussions from January through May 2012 as they reviewed numerous peer reviewed publications. Technical input reports (21) on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input. The author team’s review included a foundational Technical Input Report for the National Climate Assessment, “Climate Impacts and U.S. Transportation.”6b4d3283-49dc-4b8d-830b-aa554e37279f Other published literature and professional judgment were also considered as the chapter key messages were developed. The chapter author team met in St. Louis, MO, in April 2012 for expert deliberation and finalization of key messages.

Description of evidence base: The key message and supporting text summarize extensive evidence documented in “Climate Impacts and U.S. Transportation.”6b4d3283-49dc-4b8d-830b-aa554e37279f Specific regional climate impacts can be identified in each NCA region of the country. Specific climate impacts on transportation by region include: In Alaska, rising temperatures cause permafrost to melt, causing damage to roadbeds, airfields, pipelines, and other transportation infrastructure.6e0516e7-3e7b-42b3-be98-2740a92d2614 In the Northeast, the Chesapeake region is likely to experience particularly severe local sea level rise due to geologic subsidence,1bc74f07-688c-482c-a923-483f5d3de8b5 and increased precipitation generally (see Ch. 2: Our Changing Climate, Key Message 5, and Ch.16: Northeast), along with an increased incidence of extreme weather events. The presence of large populations with associated transportation systems in coastal areas increases the potential impacts of sea level rise, storm surge, and precipitation-induced flooding. The Southeast is subject to the interacting effects of sea level rise, increased precipitation, and other extreme events. The Southeast includes Virginia, so it shares the threat of regional sea level rise in the Chesapeake. In Louisiana, climate change poses a significant threat to transportation infrastructure of national significance.8dbd70c4-cd8c-4dce-b27c-bfb412901e58 Midwest transportation infrastructure is subject to changing water levels on the Great Lakes.4f12432e-e27d-4e72-b372-f0f9aae32ea2 Barge traffic disruptions, due to flooding or drought on the Mississippi/Missouri/Ohio river system, might be induced by changes in precipitation patterns. A major concern in the Southwest is that declining precipitation (see Ch. 2: Our Changing Climate, Key Message 5) may induce changes in the economy and society that will affect the transportation systems that serve this region. In the Southwest, rail and highway systems may be exposed to increased heat damage from the higher temperatures. San Francisco Bay, which encompasses two major airports and numerous key transportation links, is at risk for sea level rise and storm surge.561836b0-9d3d-4340-b7e9-50c2b6ce9799 Much of the economy of the Northwest is built around electricity and irrigation from a network of dams. The performance of this system may be affected by changing precipitation patterns, with potential consequences for agriculture and industry, and, consequently for transportation systems. In addition, the Seattle area may be affected by sea level rise.44e28df8-69a1-425d-9d7d-3c3c6e170564 Many relevant and recent climate data and models predict more intense precipitation events in much of the U.S., especially the Great Plains, Midwest, Northeast, and Southeast, with decreased precipitation in parts of the Southwest and Southeast (see Ch. 2: Our Changing Climate, Key Message 5).

New information and remaining uncertainties: Recent data clearly show – and climate models further substantiate – an increase in the intensity of precipitation events throughout much of the U.S. There is a need for a better definition of the magnitude of increased storm intensity so that accurate return frequency curves can be established. New regional climate model data from CMIP5 will have a significant impact on regional impact assessments. Climate and impact data desired by transportation planners may be different from the projections generated by regional climate models. This presents a number of challenges: Regional scale transportation impacts are often determined by flood risk and by water flows in rivers and streams. Flooding is, of course, linked to precipitation, but the linkage between precipitation and hydrology is very complex. Precipitation, as projected by climate models, is often difficult to convert into predictions of future flooding, which is what infrastructure designers need. Similarly, an ice storm would be an extreme event for a transportation planner, but the frequency of ice storms has not yet been derived from climate models. More generally, improved methods of deriving the frequency of infrastructure-affecting weather events from regional climate models may be helpful in assessing climate impacts on transportation systems. There are uncertainties associated with the correlation between a warming climate and increased hurricane intensity. In regions likely to see decreased precipitation, especially those areas subject to drought, stronger correlations to fire threat and lowered water levels in major waterways are needed as projections of climate models. Planning tools and models can present a step-by-step process for connecting the risk of impact with specific planning strategies such as assessing the vulnerability of existing and proposed infrastructure and then identifying key adaptation practices to address the risk.

Assessment of confidence based on evidence: Given the evidence base and remaining uncertainties, confidence is high that extreme weather events will affect transportation in all areas of the country.

References :

• Alaska’s Climate Change Strategy: Addressing Impacts in Alaska. Final Report Submitted by the Adaptation Advisory Group to the Alaska Climate Change Sub-Cabinet (6e0516e7)
• The response of Great Lakes water levels to future climate scenarios with an emphasis on Lake Michigan-Huron (4f12432e)
• SAP 4.7. Impacts of Climate Change and Variability on Transportation Systems and Infrastructure: Gulf Coast Study (8dbd70c4)
• Coastal Sensitivity to Sea Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research (1bc74f07)
• Climate Impacts and U.S. Transportation: Technical Input Report for the National Climate Assessment. DOT OST/P-33 (6b4d3283)
• Preparing for a Changing Climate. Washington State’s Integrated Climate Response Strategy. Publication No. 12-01-004 (44e28df8)
• The California Climate Adaptation Strategy 2009: A Report to the Governor of the State of California in response to Executive Order S-13-2008 (561836b0)