Partly in response to extreme weather events and major natural disasters such as hurricanes Sandy, Katrina, and Irene, massive flooding in the Midwest and large forest fires in the west, and in part due to a growing awareness of the potential threats of climate change described in research and policy studies, a growing number of transportation agencies are interested in understanding the risks associated with a changing climate.

A number of states, such as California, Massachusetts, and Washington, have legislative and executive directives for formally considering extreme weather and climate change factors in policy-making and agency decisions. At the federal level, the new Planning Order 5520 from the Federal Highway Administration (FHWA), the pilot studies on adaptation and vulnerability assessments supported by both FHWA and the Federal Transit Administration (FTA), and the new Executive Order on Establishing a Federal Flood Risk Management Standard and a Process for Further Soliciting and Considering Stakeholder Input (January 30, 2015) provide further motivation to better understand how adaptation measures need to be included in decision-making.

Although some question the projections of future climate conditions, most agree that the U.S. has experienced record extreme weather events over the past several years. The frequency and severity of such events have seemed to increase, infrastructure damage and community costs have risen, the impact of recovery costs on maintenance budgets and on regular operations activities continues to become more significant, and perhaps most importantly, public expectations of a transportation agency’s ability to recover the transportation system quickly and efficiently have increased greatly. In several instances, the recurring pressures on state transportation officials to prepare for, manage, and recover from extreme weather events have caused organizational change, the development of new management responsibilities (e.g., emergency management officials), the modification of standard operating procedures, and staff training in managing and administering recovery efforts.

WSP (formely WSP | Parsons Brinckerhoff) led the development of National Cooperative Highway Research Program (NCHRP) Report 750, Vol. 2, which recommends steps that can be taken by transportation agencies to: prepare for extreme weather events, manage agency operations during the event, and conduct post-recovery operations.

NCHRP Report 750, Vol. 2 was one of the first systematic efforts in the U.S. to identify a process for investigating the vulnerability of transportation infrastructure to extreme weather events and, over the long-term, climate change. A successful vulnerability assessment as outlined in NCHRP Report 750, Vol. 2 incorporates an appreciation of the following:

Climate Change and Extreme Weather Events Present a Wide Range of Stresses on the Transportation System

The report identified a large number of climate related stresses and resulting impacts that could affect the nation’s road network in the future. Thus, one of the first tasks of any climate change vulnerability assessment is an understanding of the types of stresses and impacts that are of most concern to the highway system managers. Depending on the type of environmental stress caused by climate change and extreme weather, a range of impacts on the highway system can be anticipated. These impacts include both impacts to the infrastructure itself (and thus how facilities are designed and constructed) and to operations and maintenance.

In addition to the direct effects of climate changes on highways, climate change will affect ecological dynamics in ways that will have implications for transportation systems. The report identifies the different types of impacts likely to be faced by transportation infrastructure, and the types of strategies that can be used to avoid or minimize the impacts. The strategies for dealing with climate change and extreme weather events will differ by functional activity within a transportation agency. For example, climate change adaptation can be considered in planning, environmental analysis, design, infrastructure retrofit, construction, operations, maintenance, emergency response and public outreach and communications. The report identifies the likely effects that a concern for climate change and extreme weather events will have on different units in a transportation agency.

Vulnerability Assessments of highways assets require several areas of expertise, including a level of engineering expertise that has at times been lacking in more policy and planning-oriented efforts.

Conducting substantive climate vulnerability assessments that can successfully lead to tangible and actionable measures is a challenge that requires experience and knowledge across a wide range of engineering disciplines. Vulnerability assessments and adaptation require an understanding of the design and operational performance characteristics of different types of assets and how these assets will respond to different types of climate and extreme weather stresses. For example, vulnerability assessments of the impacts of flooding benefit tremendously from expertise in hydrology and hydraulics and geotechnical knowledge is indispensable for slope vulnerability assessments.

Once vulnerabilities have been identified, decision-makers often want to know exactly what it means to apply an adaptation strategy to a particular asset or asset type. Cost, for example, is usually one of the most important factors for decision-makers interest and is a key factor in determining willingness to implement asset-related adaptation strategies. Likely effectiveness of different engineering strategies, under differing site and climatic circumstances, is another key factor.

Risk is a Key Factor in Vulnerability Assessments.

There is a growing understanding among researchers and highway officials that climate change and extreme weather events are a threat to many aspects of the highway system, which warrants the investigation of the specific risks it poses. Most agencies that are concerned about adaptation begin by conducting a risk assessment of existing assets.2 Most of these risk assessments remain largely qualitative and based on professional judgment, although the report presents different quantitative and qualitative approaches for considering climate change-related risks. Climate-related risk is more broadly defined in that risk can relate to impacts beyond simply the failure of the asset. It relates to the failure of that asset in addition to the consequences or magnitudes of costs associated with that failure. In this case, a consequence might be the direct replacement costs of the asset, direct and indirect costs to asset users, and, even more broadly, the economic costs to society given the disruption to transportation caused by failure of the asset or even temporary loss of its services (e.g., a road is unusable when it is under water).

An integrated risk assessment is performed on vulnerable assets with the assessment considering the likelihood of impacts and their consequences. These two factors are related to each other and their intersection determines the risk level facing an asset. Adaptation options can then be considered for high or medium risk assets while low risk assets are given lower priority.

From coastal storm surge along the Gulf Coast to high intensity stormwater runoff to melting of permafrost in Alaska, there is no one-size-fits-all solution to assessing vulnerability. How one analyzes the impact of extreme precipitation events and flooding, for example, is very different from how one would analyze higher temperatures/drought (resulting in more intense forest fires). For this reason, NCHRP 750, Vol. 2 was accompanied by a CD that allows transportation professionals to identify the type of environmental stresses of interest, the databases and approaches that could be used to analyze potential impacts, and the range of options available as part of the design process.