Recent California wildfires have damaged the Caltrans road network in 81 wildfire events, with expenditures over $590,000,000 to repair highway assets. This UC Davis research supports Caltrans’ efforts to reduce wildfire risk and improve public safety, particularly for disadvantaged communities. We conducted wildfire risk assessments for ~230,000 acres of right-of-way (ROW) land along California’s 15,000 mile highway network.
The project had four parts: 1) review and update a 2019 GIS-based wildfire risk study; 2) select maps of vegetation structure, climate change pressures, and wildfire; 3) develop a framework to use risk-based prioritized road segments with other data to further define priority ROW areas for fuels and risk reduction; and 4) interview Caltrans staff about opportunities and obstacles to increase the pace and scale of ROW vegetation treatments.
The GIS analysis comprised 21 data layers from Caltrans, the California Dept. of Forestry and Fire Protection, and US Census Bureau and Dept. of Agriculture. We updated input data and ran the model to identify priority routes for vegetation treatment, using thresholds to identify different levels of vegetation treatment need: the top scoring 10, 17, 20, and 30% of the Caltrans highway network. Results can be viewed for the whole state, or by Caltrans district or county.
We used vegetation metrics from the California Forest Observatory, including bulk density and surface fuels. We used a climate risk model that scores the relative risk to existing vegetation in three future time periods, using the MIROC RCP8.5 Global Climate Model that predicts a drier future, and greenhouse gas emission levels similar to current emission trends. We found that maps of climate change-augmented future wildfire risk were too generalized for use in planning vegetation treatments in the next five years, but did use the footprints of recent wildfires. These data layers put road segments into more general watershed- and district-level perspective, and can be used to engage local governments and fire agencies in discussions about landscape vegetation treatments.
Interviews revealed limitations of the current Caltrans vegetation control plan (vegcon) where GIS could facilitate more effective management. Currently, vegcon (essentially a spreadsheet) is used to plan activities by road segment and includes treatment regimes based on proximity to water, habitat status, and district-specific factors. Partly due to resource constraints, treatment is focused on creating an 8-10 ft. clear strip alongside the roadway. Incorporating GIS into vegcon could facilitate robust tracking and analysis to inform adaptive vegetation management, as well as inform the process with site-and watershed-scale environmental conditions and wildfire and climate risk forecasts.
Closer partnership and communication between Caltrans and local stakeholders is essential to enable management to build wildfire resilience within and beyond the ROW.