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"Climate affects the design, construction, safety, operations, and maintenance of transportation infrastructure and systems. The prospect of a changing climate raises critical questions regarding how alterations in temperature, precipitation, storm events, and other aspects of the climate could affect the nation's roads, airports, rail, transit systems, pipelines, ports, and waterways." CCSP 2008a
The changing climate poses serious challenges to the transportation community, given the community's need to watch over transportation systems and infrastructure designed to last decades or longer. Transportation functions tied to construction, operations, maintenance, and planning should be grounded in an understanding of the environment expected to support transportation facilities. Decisions therefore need to be informed by an understanding of potential future changes in climate. The understanding of climate change science and the ability to model future change continues to advance, resulting in more precise estimates of future changes in climate. However, the practitioner can be overwhelmed by the sheer volume of information, including the ensemble of models employed, the variety of emissions scenarios used to drive the modeling results, the spatial resolution of the projected climate effects, and other parameters.
The purpose of this report is to provide the transportation community (including highway engineers, planners, NEPA practitioners) with digestible, transparent, regional information on projected climate change effects that are most relevant to the U.S. highway system. This information is designed to inform assessments of the risks and vulnerabilities facing the current transportation system, and can inform planning and project development activities.
Why should the transportation community care about this information? The impacts of climate change can include weakened bridges and road beds, temporarily or permanently flooded roads, damaged pavements, and changes in road weather that can affect safety and economic activity. Understanding and proactively addressing the potential impacts of climate change can help avoid the potential damage, disruption in service, and safety concerns that climate change may cause.
Climate change information is provided in this report by U.S. region, by time horizon, and by climate variable or "climate effect" (i.e., changes in temperature, precipitation, storm activity, and sea level). The multi-state regions are identical to those included in the U.S. Global Change Research Program (USGCRP) climate impact analyses (USGCRP 2000, 2009). Three time horizons were chosen for each region: near-term (2010-2040), mid-century (2040-2070), and end-of-century (2070-2100).
FHWA's initial research efforts attempted to capture regional or sub-regional projections from all publicly available, peer-reviewed studies for these climate effects. During the course of this research, FHWA consulted with a range of nationally recognized climate scientists to ask for their insights and recommendations regarding the most credible regional projections for use by State DOTs and local transportation agencies. As a result, FHWA obtained key data sets not previously published in their entirety, including data compiled from the CMIP3 database of climate model integrations by Michael Wehner of the Lawrence Berkeley National Laboratory for the USGCRP's Global Climate Change Impacts in the United States (2009) report. These and other data sets were further evaluated and scrutinized, and subsequently vetted with a set of regional climate experts.
The results of this research provide a two-part resource to transportation practitioners:
The process used to create this report and the Climate Change Effects Typology Matrix has resulted in a unique quantitative and qualitative regional analysis of the best available climate projections. It also serves as a platform for discussions between transportation officials and climate scientists. Looking forward, the approach used here and the relationships forged in creating this set of climate information will assist future efforts to refine and disseminate information on climate effects to transportation practitioners.
Some of the findings of this report are briefly outlined below. These illustrative findings are by region and mostly for mid-century (i.e., showing projected effects in 2040 to 2070 relative to a 1961 to 1979 baseline), unless otherwise noted, and are based on averages from a multi-model ensemble for a low emission scenario (B1) as well as a moderately high ("business as usual") emission scenario (A2) (USGCRP 2009) 1 :
Recent estimates of global average sea-level rise by the end of the century range from 7 to 79 inches (IPCC 2007a; Rahmstorf 2007; Grinsted et al. 2009; Rohling et al. 2008; Pfeffer et al. 2008). Most coastal regions in the contiguous United States are expected to experience sea-level rise of this general magnitude. However, relative sea level will rise more than the global average in regions experiencing a greater rate of subsidence of coastal land (e.g., the Gulf Coast), whereas in fewer areas (e.g., parts of Alaska) local uplift will dominate and relative sea level will rise less than the global average. In addition to projected changes in vertical motion, local sea-level rise may also be affected by such factors as local changes in ocean circulation, ocean density, gravitational effects, sedimentation, and erosion.
Assessing the potential harm related to these climate effects allows highway planners to identify and address vulnerabilities. Many of the risks from climate change come from an increased exposure to weather and climate extremes. Since the highway system is engineered to withstand the historically expected range of weather stressors, small changes in average climate are not expected to cause significant impacts. However, because future climate change is projected to transcend the bounds of historic experience, it is likely to expose vulnerabilities. Impacts could include abrupt and unanticipated disruptions to the system (such as a road washing out), or more gradual disruption (such as an increased need for road maintenance).
In particular, extreme heat days, heavy precipitation events, high wind, and storm surge all pose significant risks to the highway system. For example, extreme heat causes thermal expansion on bridge joints and paved surfaces, which can result in structural degradation. Heavy precipitation events can cause flooding or mudslides that block and damage roads. High winds during severe storms can damage street lights, signs, and overhead cables. Storm surge can cause erosion of the road base and bridge supports. At the same time, climate change can reduce exposure to other risks, particularly those related to cold weather extremes. Decision makers may not wish to respond to every potential climate risk, but identifying those risks will allow them to anticipate potential disruptions and prioritize their responses.
The information in this report can help decision makers begin to address the challenges posed by climate change. It fills an important gap by providing the transportation community with information on climate change and the range of future changes in a usable format. It provides the most up-to-date information available, and is the place to start when seeking to understand how climate change may affect transportation systems and infrastructure. At the same time, this report does not answer every question on future climate change effects; research continues to progress on improving techniques for projecting and assessing climate effects and understanding extreme weather events. In the coming years, model simulations of the effect of changes in greenhouse gas concentrations on the climate will improve, and downscaling techniques that provide finer-scale climate projections will continue to evolve.