Image via Shutterstock

California’s utility watchdog worries San Diego Gas and Electric’s tree-clearing plan lacks credible science and could actually make wildfires worse.

A new safety branch of the state’s Public Advocates Office – an independent yet state-backed watchdog over the California Public Utilities Commission – is lodging some of its first complaints over San Diego Gas and Electric’s wildfire mitigation plans. In its first flexing of new muscle, the branch pored over the plans filed just a few years ago by private utilities, looking for inconsistencies or holes.

At issue is a change the utility made to the amount of trees and other brush it clears around utility poles and power lines, especially in high fire-risk areas. The required minimum is 12 feet. SDG&E wants to do 25 feet, said Nat Skinner, safety branch manager at the advocate’s office.

The first issue with this, according to the office, is ecological.

“If you clear out a whole bunch of space around the lines, grasses and non-native species that are much more fire-prone can grow underneath, which increases your fire risk,” Skinner said.

The other issue, Skinner said, is that SDG&E hasn’t provided enough evidence to back up that part of its plan.

“They provided … nothing that resembles a research plan, no timeline, no objectives,” Skinner said, even after the CPUC asked it to do so.

The advocate’s office highlighted concern over the change among 67 pages of comments on all three major California utilities’ wildfire plans back in April. But the CPUC warned SDG&E about this earlier.

In May 2019, the CPUC said it would allow “the 25-foot clearance range where necessary and feasible if supported by scientific evidence or data showing that such clearance will reduce wildfire risk.” But it then asked the utility provide “detailed guidelines” for where it wanted to do it in its 2020 plan.

It didn’t, according to the office.

The Public Advocates Office suspects if SDG&E doesn’t submit justification, it could put approval of its safety certificate in jeopardy.

That certificate gives utilities access to an over $20 billion pot of funding (paid by ratepayers and shareholders) that will help cover damage claims filed by the uninsured in the event of future catastrophic wildfires. That safety net comes with the understanding the utilities file these wildfire plans and take corrective action.

“We view pretty seriously that they’ve disregarded both a commission order and a requirement from the wildfire safety division on this,” Skinner said.

SDG&E said though the state puts a limit on the minimum tree clearance, it doesn’t set a maximum.

“SDG&E has determined that 25-foot clearances are appropriate in certain limited instances as a result of historical experience,” the utility wrote in an Aug. 17 letter to CPUC’s Wildfire Safety Division.

It referenced the deadly 2007 Rice Fire, which started when a Sycamore tree limb hit a power line near Fallbrook. That fire burned 9,400 acres and damaged 206 homes. The state held SDG&E responsible because it failed to trim back the tree.

25 Feet or 12 Feet – What Is the Difference?

Tree pruning isn’t an exact science.

Transmission lines run hundreds of miles and pass through multiple ecosystems, Skinner said. “You have to look at it area by area and base it on the benefits and the risks,” he said.

How trees coexist with utility lines
This image shows what kinds of trees can coexist with power lines based on height and distance from the utility pole. / Image courtesy of Purdue University

In heavily forested Northern California, where trees tower over power lines in some cases, branches can fall on a line and cause a spark.

Pacific Gas and Electric notes its plan is to clear trees at the CPUC’s 12-foot limit, and will “in some cases,” trim beyond that rate. Southern California Edison seems to segregate how much it cuts depending on the kind of transmission line, between 12 and 30 feet.

For brushy Southern California, it could be tree limbs or palm fronds falling on power lines, but also lines can slap together and cause a spark, which ignite underlying brush and grass.

Skinner said that improper clearing could leave space for the introduction of tall non-native grasses that burn hotter, faster and higher – adding risk to catching trees alight.

“It’s that whole process that fuels larger and devastating fires,” he said.

SDG&E said an increased risk from shrubs and bushes “has no relevance to the issue,” meaning it’s trees that matter here.

In its updated 2020 wildfire mitigation plan, SDG&E said it developed a vegetation risk index, which could help identify where it needs to do the 25-foot pruning.

But the advocate’s office said it doesn’t think that tool meets regulator’s requirement for justification.

“It is basically an asset management tool, but it is not the sole determinant of what trees or why 25 feet clearance is the right distance,” Skinner said.

In its Aug. 17 letter, SDG&E called the Public Advocates Office’s claim that 25-foot tree clearances could worsen fires “misguided.” It pointed to its own data showing that when it clears trees beyond the state minimum, its equipment had fewer contact with vegetation and a drop in fires.

Be it bush or branch, the CPUC will ultimately decide whether SDG&E’s provided enough evidence to earn the safety certificate in the near future.

(Disclosure: Mitch Mitchell, SDG&E’s vice president for government affairs, sits on Voice of San Diego’s board of directors.)

Correction: A previous version of this story misstated the width of a football field, which is 160 feet.

Leave a comment

We expect all commenters to be constructive and civil. We reserve the right to delete comments without explanation. You are welcome to flag comments to us. You are welcome to submit an opinion piece for our editors to review.

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.