CalTrans Assessment: Climate change may crack and/or wash out county highways

Caltrans releases Climate Change Vulnerability Assessment for Central Valley roads


SACRAMENTO — California’s highways have been ranked as some of the worst in the nation and it’s only going to get worse, according to a recent report released by Caltrans. 

The state agency overseeing the highway system in California released its latest Climate Change Vulnerability Assessment on how climate change will affect roadways in the San Joaquin Valley. The report evaluates risks, including extreme temperatures, increased precipitation, storm surge, and wildfire risk on highways within Caltrans District 6, the southern portion of the Central Valley encompassing Fresno, Madera, Tulare, and Kings counties, and most of Kern County. By identifying the possible risks and implications of climate change, the reports seek to guide future planning processes and investments to ensure the long-term future of California’s transportation system.

“Climate change is an immediate and escalating threat to California and its transportation system, and Caltrans is being proactive,” said Caltrans Director Laurie Berman. “We are looking at where the state highway system is vulnerable, so we can address issues moving forward.”

District 6 contains the largest portion of lane miles (with a combined length of 5,810) in the State Highway System with 476 miles of freeway and 1,554 miles of rural and urban highway along 33 state highways wholly or partially located within the district. Interstate 5 and State Route 99 run the length of District 6—they are the main north-south arteries for not just the Central Valley, but for the entire state. These two routes carry a significant amount of truck traffic that is vital to the agricultural base of the region. But the real concern are the smaller east-west highways (SR 140, SR 152, SR 180, SR 198, and SR 46).

Extreme weather and its associated costs are expected to become more pronounced and more frequent in the future as a result of climate change. Events are tied together, as a wildfire can scorch crucial vegetation on hillsides that would otherwise help soak-up storm runoff in the winter. This can lead to flooding and severe erosion of state roadways.

The report notes that the San Joaquin Valley is experiencing hotter, longer summers and drier winters with minimal to no rain, particularly during the most recent drought. During the drought, groundwater pumping, largely for crop irrigation, caused subsidence in the San Joaquin Valley, and may have permanently decreased aquifer capacities. The worst drought in 1,200 years was followed by a flood year with precipitation levels at 178 percent of normal.  Winter 2017 brought historic snowpack to the Sierra Nevada Mountains, which melted at overwhelming rates during the hot summer of 2017. In June 2017 outflows from Pine Flat Lake in Tulare County were increased to make room for more snowmelt, but that caused flooding downstream in Kingsburg. Intense storms can cause roadway flooding and transportation infrastructure washout requiring millions of dollars in maintenance and repair costs. 

“Caltrans expects the effects of climate change to increase the frequency of events of this scale,” the report states. “It is important that responses to these events, and similar future events, increase system resiliency and address potential future conditions.”

The report is supported by an extensive GIS database and Caltrans has developed an interactive mapping application for public use, which shows impacted locations and the climate model results. Temperatures across District 6 are expected to increase considerably by the year 2100, which will necessitate a review of roadway pavement design parameters. The eastern, mountainous regions of District 6 will likely show the greatest temperature increase. In Fresno, Madera, and Tulare Counties, the average weekly high temperature is expected to increase by 2 to 4 degrees by 2025. By 2085, Tulare County’s average maximum temperature will increase by 6-8 degrees on average but areas such as Woodlake, Lemon Cove and Three Rivers are expected to increase by as much as 12 degrees on average.

The maps of 100-year storm depth change for District 6 show the midpoint of predicted precipitation increase. The data shows that the more-mountainous regions of District 6 will likely have the greatest change in 100-year precipitation depths. The most significant increase is in Tulare County, where depths are projected to increase by around 15% by mid-century. Increases in precipitation could result in flash flooding, which may submerge, displace, scour, or erode elements of Caltrans infrastructure. To better understand the potential effects and potential adaptation measures, detailed precipitation and flooding analyses of Caltrans infrastructure will be necessary.

The models show that Tulare County has 85 miles of roadway with a wildfire exposure level of moderate to very high, with highways 245 north of Woodlake, 198 east of Exeter and 190 east of Springville being the most vulnerable to wildfire risk. These highways are critical for access to foothill communities of the district where there is less redundancy in state routes, unlike in the Valley floor, where highways running in parallel are more common. In the event of a major wildfire, these routes would be crucial as evacuation routes and as entry ways for emergency responders. The reports and the interactive mapping application can be accessed at:

Using data from the studies, Caltrans intends to help evaluate the vulnerability of other modes of transportation through partnerships and data sharing with local and regional agencies. As Caltrans moves towards a resilient transportation system, the department will continue to enhance its climate change efforts and partnerships with local, regional, state and federal agencies in order to create coordinated adaptation solutions for the state transportation system. 

Once system vulnerabilities are identified, Caltrans will begin considering enhanced system resiliency when choosing projects and project designs. In District 6, adaptive responses will be needed to address the wildfire, precipitation, and increased temperature effects that are expected to occur. These strategies may include: 

  • Increasing drainage structures and capacity in areas where wildfires are projected to occur, and installing slope stabilization strategies outside of the roadway right-of-way where landslides are an additional concern. 
  • Increasing culvert size or installing new, larger culverts where there are anticipated increases in precipitation and flows. Bridges may need to accommodate for larger river flows and increased scour. 
  • Extending pavement life by installing pavement that retains its strength and quality when exposed to higher temperature conditions. These efforts will require Caltrans to be proactive and invest in the long-term viability of the transportation system.

Caltrans has been considering the impact of climatic changes on the state transportation system and developed guidance and studies on how climate change can be incorporated into planning and project design. This also aligns with Governor Edmund G. Brown Jr.’s call to integrate climate change into transportation investment decisions through Executive Order B-30-15. For more information visit:

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