addressing climate change adaptation in regional transportation plans

Addressing Climate Change Adaptation in Regional Transportation PlansA Guide for California MPOs and RTPAsexpected volumes, for example) and many directly address the specificstresses of climate. The Caltrans Standard Specifications and HighwayDesign Manual are primary resources, to be supplemented withapplicable national (e.g., AASHTO) and local specifications or guidelines.c. Prior research. Several published or forthcoming resources addressvulnerability thresholds for transportation infrastructure, includingClimate Change Adaptation and the Highway System (NCHRP, forthcoming)and the FHWA Climate Change Pilot reports (2011, various authors).d. Informed hypotheses. The objective of the exposure exercise is to rapidlyidentify the basic potential for significant impacts, and then movequalifying assets into the risk assessment phase for further study. Thecreation of a nonstandard exposure threshold, either in the absence ofother guidance or to correspond with specific climate or transportationattribute data, is acceptable as long as doing so supports this objective.Hypothesized or proxy thresholds, especially those generatedcollaboratively by qualified professionals, can add value to theassessment process.The thresholds test supports the application of rules of thumb concerning thesusceptibility of assets or asset types to climate events of a given severity orfrequency in order to estimate the potential for climate impacts. Climate impactsare, in effect, the intermediaries between stressors and the expectedconsequences of extreme climate events, describing what might actually happento the asset. For instance, extreme rainfall is a stressor, whereas flooding is therelated impact from which consequences may stem directly (some impacts maybe 3 rd or even 4 th order effects of stressors). If it is known, or even estimated, thatthe one-percent chance rainfall is the threshold that leads to a specific impact ofconcern (e.g., flooding), then it may be assumed that the asset is both exposedand susceptible if the threshold is exceeded.Consider a sample asset/stressor pairing, a scour critical bridge and extremerainfall. The rainfall event itself may not detrimental to the bridge, but intenserainfall may concentrate as runoff, engorge a nearby river or stream, increase theflow rate, and thereby promote scour – the climate impact. The same scenariocould also lead to inundation of the bridge’s approaches – another climateimpact. Some climate impact pathways will be simpler – high ambienttemperatures can lead to extreme surface temperatures, which, depending on thesurface, leads to rutting or detrimental expansion. This is where conditioninformation can be factored in at a systems level, if applicable, to help establishsusceptibility.In many instances, it will be preferable to combine the geospatial and thresholdtests. Flooding, for example, is geospatial, but mapped floodplains or hazardareas typically correspond to a threshold event – for example the 100-year (onepercentchance) flood. In turn, some transportation infrastructure, such asculverts, is typically sized for specific design events – again, often the one-11-6 Cambridge Systematics, Inc.