Mapping powerline ignitions and efficacy of wildfire mitigation strategies in California

Abstract Powerline ignitions lead to disproportionately large fires, accounting for about a quarter of the most destructive fires in California’s history. In response, electric utilities have deployed fire mitigation strategies, including line treatments and strategic de-energization. Given mitigation costs, spatial optimization is critical to prioritizing risk reduction efforts, however, little research exists examining the geography of these ignitions and the efficacy of these strategies. Here, we explored the spatial and temporal patterns of powerline ignitions and mitigation strategies for the three largest investor-owned utilities in California from 2014–2024 and evaluated whether these strategies are effective at preventing ignitions, particularly those with the potential to become large fires (>100 acres). Approximately 1% of over 6000 powerline ignitions from 2014–2024 became a large fire. Nearly two-thirds (64%) of forested distribution circuits had at least one ignition, largely due to vegetation contact and equipment failure, while powerline ignitions in flammable shorter vegetation were less frequent and mostly due to equipment failure. The ignition rate was about 4 times higher on distribution lines than on transmission lines, while the ignition rate for large fires was similar between transmission and distribution lines. Older, bare lines had higher ignition rates on both distribution and transmission lines. For distribution lines, however, similar ignition rates were observed for partially covered and partially undergrounded lines. Strategic de-energization on distribution lines was associated with reduced ignition rate, though we did not account for confounding factors that may have also reduced ignition rate. Conversely, the ignition rate increased on transmission lines during 2014–2024, and de-energization was utilized less frequently on these line types. Additional research is needed to better understand how targeted powerline fire mitigation strategies can be better deployed to lower fire risk.