CalTrans Climate Change Vulnerability Assessment 2018 Summary Report - District 4

The California Department of Transportation (CalTrans) vulnerability assessment of California’s District 4 (9 San Francisco Bay area counties) is a result of the 2013 CalTrans report on the department’s activities and plans to address and adapt the sector to climate change. The vulnerability assessment summary report describes the impacts of climate change on California’s Highway System in District 4, and a companion Technical Report describes the processes used to identify these impacts. The findings will inform the way in which CalTrans plans, designs, builds, and maintains highways within this district. This is the first of 12 vulnerability studies that will eventually cover each district in the state.

The report develops a vulnerability definition and approach that recognizes the various practices of CalTrans. The approach includes the following three actions:

  • Exposure: identification of CalTrans assets exposed to damage from future conditions
  • Consequence: determination of what may occur to the system assets from climate change (in loss of use or costs to repair)
  • Prioritizations: developing a method by which capital programming will be made to address identified climate-related risks

CalTrans expects an increase in extreme weather events in the region due to climate change. The report describes that “in the last year alone, Caltrans has sustained approximately $1 billion in storm-related damages.” The assessment primarily examines the vulnerability of the state’s highway system to the increased risks from rising temperatures, increasing precipitation, wildfires, sea-level rise, storm surges, and combined climate effects. The report identifies the risk posed by each climate impact, and provides suggested actions in response to these impacts on transportation infrastructure:

  • Temperature: Higher temperatures cause pavement to wear faster, and increases maintenance costs. Development and maintenance of roads need to consider increasing temperature as a part of pavement design.
  • Precipitation & Storm Surge: Increased rainfall, along with sea-level rise, will increase flooding in low lying areas. In order to improve the long-term resiliency of the state highway system, CalTrans needs to implement more natural drainage systems in flood-prone areas.
  • Sea Level Rise: Rising sea levels can exacerbate tidal flooding and storm surge conditions along the California coast, leading to greater coastal erosion and cliff retreat and impacting coastal roads. CalTrans is currently working on the Devil’s Slide Project which incorporated the effects of climate change in coastal tunnels in District 4.
  • Wildfire: Fires can exacerbate flooding by denuding hillsides of vegetation and reducing the permeability of soils which can both lead to higher runoff levels and debris that clogs culverts. CalTrans is currently working to define actions that may need to be taken to address the potential future impacts of wildfire.

The assessment also discusses how combined climate effects will severely impact transportation infrastructure when two or more extreme climate events happen at the same time. For example, wildfires were found to make soils less likely to absorb rainfall, which can result in higher levels of flooding when there is an increase in precipitation or storm surge.


Publication Date: January 2018

Related Organizations:

  • California Department of Transportation (Caltrans)


Resource Category:

Resource Types:

  • Assessment

States Affected:


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