Infrastructure Climate Resilience for the National Forests of California
The Sierra Nevada and Coast Range mountains of Southern California contain 14 National Forests and a huge amount of infrastructure, including 31,300 miles of roads, 12,500 miles of trails, 725 bridges, 208 dams, and over 6,350 buildings, all managed by the US Forest Service. Over the last 40 years these regions have been hit by numerous climate change-related events including droughts, major forest fires, and major storms with floods. Billions of dollars in damage have been sustained and numerous lives lost as a result of these events.
To address these issues, state and federal agencies, including CalTrans, CALFIRE, Federal Highway Administration, and the U. S. Forest Service have been involved in development of resilience strategies. A Climate Vulnerability Assessment and Adaptation Strategy Partnership project by the U. S. Forest Service in California, has included Infrastructure, Recreation, and Ecosystem Services to evaluate climate change impacts and solutions. Project work has involved synthesizing the best available information on climate change; climate model studies of future anticipated weather conditions and storm events; community and agency outreach for understanding climate impacts; a review of assessment methods to evaluate risk and prioritize work; development of ArcGIS tools and story maps for geospatial information; identification of road adaptation and resiliency strategies and measures; and publication of these findings in peer-reviewed GTRs.
Climate forecasts for most of California show a future hotter climate with long periods of dryer conditions mixed with periodic wetter periods. Precipitation models are varied with some areas increasing and other areas drying. Storms are predicted to be more intense, with the development of “atmospheric rivers”. Overall, there is considerable uncertainty in the climate forecasts, depending on the greenhouse gas emission scenarios used, but warmer conditions, more droughts, more intense fires, and more severe flooding can be expected in the future.
To adapt to the likely future climate conditions, a number of road and structure adaptation and “stormproofing” measures have been identified to reduce the vulnerability or risk of damage. Identified adaptation measures include defensible space around structures such as bridges and buildings; construction with non-flammable materials; timely road maintenance; positive road surface drainage systems to prevent accumulation of water on the road; adequate culvert and bridge scour protection; trash racks on culverts and stream diversion prevention measures; conservative drainage designs and use of “stream simulation” concepts; roadway surface stabilization methods; cost-effective slope stabilization measures such as deep patch, bioengineering, and geosynthetic reinforced soil slopes; and erosion control measures with thorough ground cover, and use of deep-rooted vegetation.