(posted to the new What’s Natural? column, Pacifica Tribune January 2, 2019)
A Look at Wildfires
In early December I surveyed the horrific Camp Fire disaster in Paradise. Having been director for 25 years of a university field station located in the heart of the Tahoe National Forest, I’ve been a “student” of fire ecology for 30 years and wanted a closer look at why row after row of homes completely incinerated while surrounding trees were merely scorched, with leaves and needles browned but not burnt?
Large fires have recently ravaged about 1.8 million California acres a year, prompting media and politicians to proclaim a “new normal” that’s “evidence of global warming”. But UC Berkeley fire ecologists have calculated that before 1800, fires burned 4 million California acres each year (despite cooler temperatures). So what natural fire dynamics promote such extensive burning?
Wildfires have indeed increased since 1970, but that’s relative to previous decades of intensive fire prevention. As fire was recognized as a natural and necessary phenomenon for healthy ecosystems a new era began. In the 70s the US Forest Service moved away from extinguishing all fires by 10 AM the day after detection, switching to a “let it burn policy” if human structures were not endangered.
Paradise, unfortunately, sprung up amidst a forest dominated by Ponderosa pines. Largely due to frequent lightning strikes and dry summers, Ponderosa habitat endures fires about every 11 years. Fortunately for California’s coastal residents, lightning is rare. However, both regions are vulnerable to human ignitions, which start 85-95% of all fires. Recognizing this growing problem, a bipartisan bill was presented to Governor Brown two years ago to secure our power grid. Shockingly he vetoed it. That was a bad choice given the Camp Fire, Wine Country Fires and many more were sparked by an ageing electrical infrastructure. Recent studies show larger fires result from a confluence of human ignitions and high winds. But it is not just random coincidence. The high winds that spread these massive fires also blow down power lines that ignite those fires.
Human ignitions versus natural from Balch 2017
In 2008 the world’s foremost expert on fire history, Stephen Pyne lamented, “global warming has furnished political cover to encourage certain fire management decisions while allowing climate to take the blame.” How true. Both PGE and Governor Brown have blamed wildfires on climate change.
When you build a camp fire, you intuitively understand fire ecology basics. You do not hold a match to a log no matter how dry. You start a camp fire with kindling. Fire ecologists call forest kindling, like dead grass, leaves and small shrubs, “fine fuels”. In dry weather “fine fuels” become highly combustible in a matter of hours, or at most days, even during the winter. Furthermore, California’s summer climate is naturally dry for 3-4 months, creating highly combustible habitat each and every summer.
Additionally, camp fires only smolder without enough air, so we huff and puff to get a burst of flames. Likewise, high winds turn a spark into a major conflagration. It was strong winds that rapidly spread the Camp Fire. The fast-moving flames, feeding on “fine fuels” littering the forest floor, generated enough heat to ignite flammable homes that then burned from the inside out; but only enough heat to char the bark of most surrounding trees.
Miraculously spared buildings dotting a devastated landscape made the case for creating “defensible spaces” by managing the “fine fuels”. Surveying one unscathed church, the fire clearly came within 100 feet, scorching the base of every encircling tree. But due to a parking lot and a well-manicured lawn, the lack of “fine fuels” stopped the fire in its tracks. Trees on the lawn were not even charred. The public would benefit greatly if wildfire news stories emphasized the need to create adequate defensible spaces.
With high deserts to the east and the ocean to the west, California’s winds shift with the seasons. Land temperatures always change faster than the ocean’s. In the summer, warmer land surfaces draw in moist sea breezes. The resulting fog moistens coastal landscapes and reduces fire danger there. Thus, any warming, whether natural or CO2driven, should increase the fog.
In the autumn, the land cools faster than the ocean causing the winds to reverse direction. The colder it gets, the stronger the winds blow from the high deserts towards the coast, peaking in December. These winds are called Santa Annas in southern California. The Wine Country fires were spread by the Diablo winds. But regardless of the name, the science is the same. Accordingly, it was November winds that fanned a spark into an inferno aimed directly at the heart of Paradise.
It has long been known that due to these autumn and winter winds, much of California endures a dangerous fire season year-round. On the optimistic side, any warming of the land during the cool seasons, whether natural or CO2 driven, should reduce these winds. Indeed, the natural drivers of wildfire are very complex, and maintaining a defensible space is our safest bet.