Even as San Francisco dries out from an epic storm soaking the region over the past two days, Caltrans is thinking ahead to the future when climate change will make large, violent storms more common, along with arid, dry stretches without any precipitation.
In a recent report, Caltrans ponders the likely effects of climate change on Bay Area roads. Highways “serve as evacuation routes for community members, critical access links for emergency responders, [and] essential arteries required to move equipment and supplies needed to facilitate recovery efforts,” says Caltrans, but they may also be highly vulnerable themselves when needed most.
And the slate of disasters and potential disasters that the state is bracing for between now and 2085 reads like a list of Biblical judgments: fires, floods, landslides, and storms across the board.
Here’s a few of the dangers from on high that the region will be grappling with a generation from now:
- The heat. Even regular high temperatures may passively damage roadways, as asphalt is hardly impervious to the heat: “Materials exposed to high temperatures over long periods of time will deform (such as pavement heave or track buckling). The eastern area of District 4 [the Bay Area] is expected to show the greatest increase in temperatures, with the average high temperature for one week increasing by an estimated 4-5 degrees (F) by 2025 and 8-9 degrees (F) by 2055.”
- Wildfire. This year’s hellish October fire season in the North Bay gave the state some notion of what the future may hold. Strangely, one of the biggest risks to roadways after a fire is flooding: “Wildfires can often have an impact on soils, making them less permeable (hydrophobic) and so reducing their ability to absorb rainfall. The result is flooding patterns that are inconsistent with original design assumptions, since the land is no longer able to help control rainwater flows. Land stripped of vegetation is also more susceptible to shallow landslides.”
- Erosion and hill collapse: Previous generations built California with certain assumptions about what constituted normal weather. A California where storms are less common but more violent when they happen can pull the rug out from under state infrastructure: “California’s recent rainy season after a five-year drought has caused severe flooding, landslides, and coastal erosion, totaling over $1 billion in highway damage for Caltrans. [...] Hillsides that burned during wildfires last year crumbled during the winter’s record-breaking rain and snow storms. Between January and May of 2017, District 4 experienced weather- related damages in 110 locations, with a cumulative cost over $250 million in repairs, largely from heavy precipitation and strong coastal storms.”
- Sea levels and storms: Right now, Caltrans anticipates that a once-in-a-century storm would put about 5.6 miles of highway underwater in Alameda County, and 10.6 in Marin County. By 2055, those projections rise to 10 and 13.5 respectively. By 2085 they become 25.3 and 19.5. “Many of these state highways are critically important not only for the San Francisco Bay area but also for serving intra-state travel and commerce,” but could be impassable during a true emergency.
You can read the rest of the Caltrans vulnerability report here, or a more technical explanation of the projected effects here.