In October 2007, wildfires burned hundreds of square miles in Southern California, and many of these were thought to have been ignited by overhead utility power lines and aerial communication facilities near power lines downed by powerful winds. In response to these wildfires, the California Public Utilities Commission (CPUC) began to consider and adopt regulations to protect the public from potential fire hazards associated with powerline and nearby aerial communication facilities.

Many of these new regulations relied on interim maps that designated areas where there was an elevated hazard for powerline fires to occur and spread rapidly. These are known as “Fire-threat maps,” and each map covered a different part of California. However, these did not cover the entire state and in 2015 the CPUC decided to (1) develop and adopt a permanent fire-threat map that covered the entire State; and (2) incorporate into the California General Order 95 (which addressed wildfires) a new High Fire-Threat District based on the newly adopted fire-threat maps; and (3) consider and adopt new fire safety regulations for electric utilities and communication structures in the High Fire-Threat District.

To help California with these needed maps, SIG scientists worked with CALFIRE and the Desert Research Institute (DRI). The research team used the Weather Research and Forecasting Model (WRF), a mesoscale numerical weather prediction system designed for both atmospheric research and operational forecasting applications that has over 39,000 users worldwide. Using this model, they inputted 10 years of hourly, 2km-gridded weather data for all of California; these data were then calibrated to local historical weather readings from around the state. From this enormous weather dataset, the top 2 percent worst fire weather conditions were extracted for each 2km grid cell. These conditions were then used to perform 1000 unique, high-resolution wildfire simulations per cell; simulations were based on the USGS-supported LANDFIRE 1.3 dataset. In total, SIG scientists simulated over 100 million ignition events around the state of California under extreme historical weather conditions.

The results of these simulations were aggregated to create numerous 2km-resolution fire risk and fire behavior distribution maps, which are now helping planners understand where are the areas of greatest fire risk across the state. In particular, these maps are being used by planners at the CPUC, who are employing them to determine what utilities are most at risk. Once risks are known, the necessary preparatory actions can be planned and implemented, helping to protect the utility infrastructure and to reduce the potential of impacts caused by utility fires.

As of January 19, 2018 the CPUC adopted, the final CPUC Fire-Threat Map, available here.