  As wildfires in the United States are becoming more frequent and severe,
mitigating wildfire ignition risk from power line faults is an increasingly
crucial effort. Long-term ignition prevention strategies, especially converting
overhead lines to underground cables, are expensive. Thus, it is important to
prioritize upgrades on lines that will reduce wildfire ignition risk the most.
However, since so many factors contribute to ignition risk, it is difficult to
quantify the wildfire risk associated with power lines. This paper examines how
various risk definitions based on historical wildfire risk maps can be used to
inform transmission upgrade planning. These risk metrics are evaluated using an
optimization model that determines which overhead lines should be undergrounded
such that the total wildfire risk in the network is minimized. The risk
assignment and upgrade selection are tested on both a synthetic network and the
actual transmission lines in California.
