addressing climate change adaptation in regional transportation plans

Addressing Climate Change Adaptation in Regional Transportation PlansA Guide for California MPOs and RTPAsexample, bridges), or based on other criteria important to the region. The climatedata accompanying this report has been provided for the following periods:Present conditions. Climate information for present conditions refers to datareflecting the current status of a given climate stressor. Data for presentconditions will be used as the baseline to which future time horizons arecompared and the magnitude of change will be ascertained. Typically,present conditions stressor levels are calculated as historic average overmultiple years (i.e., 1970-1999).Future conditions. Future climate projections are often averaged overmultiple years to reduce the spread of year-to-year variability and reflect thegeneral trend of expected changes. Typically, projection periods are dividedinto equal intervals for climate trend averaging such as decadal averages or30-year averages. As such, the climate conditions for future analysis yearsshould represent an average of the climate trend over a period of severalyears around the time period selected.Identify Stressor Types and ThresholdsIn this context, the term “climate stressors” refers to climate conditions that posepotential hazards to transportation assets, many of which are projected toincrease in frequency or severity in the future. Examples of climate stressorsinclude temperature, precipitation, and sea-level rise. Geospatial climatedatasets can be used to aid in characterizing the magnitude of change in thesestressors, enabling an analysis of the vulnerability of critical transportation assetsto these changes. Potential stressor impacts on transportation assets mayinclude:Temperature. A primary variable affecting transportation asset vulnerabilityis the average number of high heat days occurring within a given year. Forexample, exposure to high temperatures can degrade the material strength ofbinding materials in asphalt and may leave roads vulnerable to damage.Quantifying the number of heat days in a given region under existing andfuture conditions will aid in identifying the regions and assets most likely tobe impacted by rising temperatures.Precipitation. Design of drainage capacity for transportation assets relies onknowledge of return periods for rainfall and streamflow conditionsestablished over years of historical measured data. Climate projectionsindicate that extreme precipitation events are likely to increase in frequencyand severity, which may alter the expected return period of a given rainfalldepth or streamflow peak. Knowledge of expected changes in precipitation,and associated hydrologic variables including snowpack, runoff, andbaseflow, will be critical for evaluating the vulnerability of drainage systemsfor various transportation assets.Sea-Level Rise. Impacts to transportation assets from extreme tide levels,exacerbated by net increases in sea level, include the increased frequency,extent, and depth of inundation. Sea-level rise is also expected to increase the10-4 Cambridge Systematics, Inc.