addressing climate change adaptation in regional transportation plans

Addressing Climate Change Adaptation in Regional Transportation PlansA Guide for California MPOs and RTPAsInterpreting and Using Extreme Temperature DataAs an example of evaluating extreme temperature data Figure 10.2 containsgeospatial and tabular data representing the geographic distribution of days per yearexceeding 95°F under present conditions (30‐year annual average from 1970 to1999), and three future periods: 2010 to 2039, 2040 to 2069, and 2070 to 2099. Thegraphic includes data for both A2 and B1 emissions scenarios, and represents anaverage of data from six GCMs. This information was computed using dailytemperature data from downscaled GCM output downloaded from the CMIP3 publicarchive (http://gdo‐dcp.ucllnl.org/). Extreme temperature information can be viewedin a similar layout on the Cal‐Adapt website (http://cal‐adapt.org/). For thegeospatial map data shown in the figure, the annual number of days exceeding theextreme temperature threshold was tabulated and averaged for the 30‐year periodsrepresenting present and future conditions. The procedure depicted in Figure 10.2was repeated for each grid cell to generate a map of extreme heat days for futureconditions.Figure 10.2 Geospatial Layers Created on Temperature DataSource: ESA PWA, 2012.Note:The data used to generate this figure was retrieved from the CMIP3 archive on 8/9/2011. A technicalsummary of the data sources and computational methods applied for generating the climate data can berequested separately through Caltrans.Extreme Precipitation ThresholdA useful indicator for evaluating impacts to transportation infrastructure fromprojected changes in precipitation is the return frequency of today’s 100-year(one-percent chance) rainfall event. Design guidance for transportation drainageoften mandates or advises providing adequate capacity to manage the 100-yearstorm. Under the influence of climate change, the absolute amount of rainfallcorrelated with today’s 100-year event may recur with greater frequency in thefuture. Evaluating the range of potential rainfall totals corresponding to theprojected 100-year rainfall event can be useful for understanding the degree ofchange in precipitation that will need to be accommodated in the drainage10-6 Cambridge Systematics, Inc.